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Journal of Materials Science (15734803) 59(17)pp. 7218-7234
This paper presents the nickel–cobalt nanoprickly particles (PNi2Co3) composited with graphene nanosheets (GNs) and carbon nanotubes (CNT), prepared via the one-pot hydrothermal method (PNi2Co3/GNs/CNT), as an efficacious nonprecious metal bifunctional electrocatalyst for both oxygen evolution and reduction reactions (OER/ORR). The study employs a comprehensive methodology, incorporating cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) analysis to characterize and assess the materials and electrochemical properties investigated in the article. The primary objective was to successfully prepare a bifunctional electrocatalyst, and the PNi2Co3/GNs/CNT material achieved this goal. It exhibited superior OER activity, durability, and resistance to crossover effects, by an overpotential (η) of 480 mV and a Tafel slope of 61 mV dec−1, significantly higher than those obtained for RuO2 nanoparticles (η = 970 mV, Tafel slope = 85 mV dec−1). A similar trend was observed for ORR, where the PNi2Co3/GNs/CNT displayed high activity with an n = 3.93, close to the activity of a Pt/C (20 wt%), commercial catalyst with n = 4. Careful analysis of the EIS results via suitable models, in conjunction with Tafel data, revealed that the enhanced activity originates mainly from two factors: (a) the large surface area of the Ni–Co nanoprickly alloy and graphene sheets, where the CNTs (as a spacer) helped graphene nanosheets to avoid restacking and decreasing the surface area, and (b) the synergistic effect between Ni–Co nanoprickly and carbon components (GNs and CNT) of the composite. Graphical abstract: (Figure presented.). © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.
Electrocatalysis (18682529) 15(1)pp. 29-41
Here, a general method for fabricating active electrocatalysts is introduced for oxygen evolution reaction (OER) based on multimetallic (ternary alloy) structures formed on the N-doped nanoporous carbon platform without using ruthenium or iridium. Accordingly, three different sizes, small, medium, and large, of cobalt zeolitic imidazolate framework-67 (ZIF67X, X: S, M, L) are synthesized. Then, the product is carbonized via direct pyrolysis at 800 °C in an argon atmosphere to yield nitrogen-doped nanoporous carbon composited with cobalt nanoparticles (PZIF67X 800). To improve the activity, the most active nanoporous system for OER (PZIF67L 800) is further modified by electrochemical deposition of Co, Ni, and Fe (PZIF67L 800-CoNiFe). The electrochemical results revealed a large electrocatalytic activity for the GC-PZIF67L 800-CoNiFe toward the OER in alkaline media, Tafel slopes of 72 mV dec−1 and overpotentials of 314 mV at 30 mA cm−2 (η30), compared with those obtained under the same conditions on GC-RuO2 (99 mV dec−1 and 499 mV). The improved activity is attributed to (i) the increase in active surface area and simultaneous formation of Co nanoparticles and nitrogen-doped porous carbon, causing uniformly dispersed metal nanoparticles in the composite, and (ii) synergistic effect between the ingredients of ternary alloy nanoparticles (CoNiFe-NPs) and nitrogen-doped carbon nanoporous platform. Graphical Abstract: [Figure not available: see fulltext.] © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Torabi, M. ,
Karimi shervedani, R. ,
Shahrokhi, S.M. ,
Khosravi, M. ,
Mohagheghnia, M. ,
Hakami shalamzari, Y. Journal of Energy Storage (2352152X) 102
This research introduces the supercapacitive behavior of porous coral-like nickel-cobalt-phosphide composited with reduced graphene nanosheets (RGNs) using a straightforward one-step hydrothermal process. Several surface and electrochemical methods were used to follow the fabrication and study the electrochemical behavior and supercapacitive charge storage performance of the composite (NiCoP/RGNs) and its ancestors (NiP, CoP, NiP/RGNs, and CoP/RGNs). The effects of each component, NiP, Co, and graphene, on the performance of the composite were studied. In the composite with the optimum proportion of ingredients, the presence of NiP contributed to the high specific capacity, Co enhanced the intrinsic conductivity and electrochemical activity, and graphene significantly increased the surface area and electrical conductivity, leading to improved overall performance of the NiCoP/RGNs composite. The NiCoP/RGNs composite exhibited a uniformly shaped porous nanostructure with coral-like morphology and superior specific capacity of 982 C g−1 at 1 A g−1 (2455.6 F g−1), which can be attributed to its substantial specific surface area, notable intrinsic conductivity, and fleeting reversible faradic reaction properties. The asymmetric supercapacitor (ASC), made up of stainless steel modified with NiCoP/RGNs as a positive electrode and industrial active carbon as a negative electrode, revealed a high energy density of 54.63 W h kg−1 at a power density of 749.49 W kg−1 with 81 % capacity retention after 4000 cycles. The research may open up possibilities for the one-step, straightforward production of highly porous bimetallic phosphide materials, combined with graphene nanosheets, to store electrochemical energy. © 2024 Elsevier Ltd
Colloids and Surfaces A: Physicochemical and Engineering Aspects (18734359) 677
Conjugation via covalent bonding on nanocarriers is an effective strategy to stabilize drugs and prodrugs, improve their efficiency and decrease their side effects. In this study, temozolomide (TMZ) is used as a prodrug and stabilized via covalent conjugation on folic acid−targeted−gold−thiol modified surface, and then, the physicochemical behavior of the integrated system towards cancer cells is studied by surface techniques, votammetric methods, electrochemical impedance spectroscopy (EIS), and quartz crystal microbalance (QCM). The voltammetric and ATR−FTIR studies revealed that the conjugated TMZ is stable at least for 48 h. The adsorption behavior of A2780 cancer cells onto the system is well described by Freundlich adsorption isotherm with adsorption capacity of 50.11 and adsorption intensity of 1/n = 0.15. The process is controlled by a first order kinetic model with rate constant of 0.036 ± 0.002 min−1 and t1/2 of 18 ± 1 min. To our knowledge, this is the first time that the physicochemical behavior of the TMZ prodrug integrated onto Au−thiol SAM nanostructures is studied by EIS and QCM concerning cancer cells. The results of this research are noteworthy and can improve our physicochemical insights into anticancer drugs in conjunction with gold targeted nanocarriers, regarding the stability of prodrugs, mixed molecular nanostructures, adsorption kinetics and isotherms for sensing and capture of cancer cells. © 2023
Journal of Drug Delivery Science and Technology (17732247) 72
Here we report synthesis and characterization of a biocompatible and biodegradable nanocomposite based on paramagnetic Mn–ZnO NPs as a tumor diagnostic agent, coated with polyacrylic acid, decorated and loaded with folic acid and doxorubicin, Mn–ZnO@PAA/FOA(Dox)load. The Mn–ZnO NPs were prepared under the coupled microwave-hydrothermal controlled conditions, leading to 42.00 ± 3.00 nm paramagnetic Mn–ZnO NPs, appropriating for theranostic applications. The several surface, solution, and electrochemical techniques approved successful fabrication of the nanocomposite. The application of nanocomposite was tested for A2780 cancer cells. In effect, the in-vitro MRI measurements, the drug release experiments, and the MTT assay, were performed, respectively, to show diagnostic efficiency, applicability of the nanocarrier as a pH-sensitive for Dox delivery, and the biocompatibility and also theranostic efficiency of the targeted nanocomposite system. The quantitative results obtained through in-vitro tests showed that the system has potential application as a contrast agent in MRI with relaxivity (r1) of 35 mM−1 s−1 for Mn–ZnO NPs in the Mn concentration range of 0.06–0.52, which are significantly improved, compared with our previous works. The Dox drug was released from the system more efficient and faster at pH 5.4 than 7.4, supporting the pH sensitivity of nanocarrier. The in-vitro biocompatibility studies showed that the Mn–ZnO@PAA/FOA NPs (having no Dox) are not toxic, while the Mn–ZnO@PAA/FOA(Dox)load NPs inhibited proliferation of the A2780 cancer cells more effectively, compared with HFFF2 normal cells. Based on the electrochemical impedance spectroscopy results, the Mn–ZnO@PAA/FOA(Dox)load NPs capture the A2780 cells significantly larger than the HFFF2 cells. © 2022 Elsevier B.V.
Journal of Drug Delivery Science and Technology (17732247) 67
Targeted drug delivery systems have been designed to improve the efficiency of therapeutic and diagnostic agents. This strategy can also reduce the toxicity associated with these agents. Herein, a targeted imaging and therapeutic nanocomposite system, consisting of AuNPs double coated by MnCO3/Mn3O4 and polyacrylic acid, as CT-scan and MRI contrast agent, conjugated with folic acid, and loaded with doxorubicin and propidium iodide, as targeting, therapeutic and fluorescence agents, AuNPs@MnCO3/Mn3O4@PAA-FOA (Dox&PI)load, is reported. The performance of the system is supported by the following findings: (i) The MRI efficiency and pH sensitivity of the MnCO3/Mn3O4 nanocomposite supported by the MRI relaxation rates, 12.62 and 1.32 mM−1 s−1, obtained respectively at pHs of 5.5 and 7.4. (ii) The efficiency as well as the synergistic effect between the PI and AuNPs for enhancing the contrast of CT images revealed by the slopes of Hounsfield unit vs. system concentration, 23.22 and 32.63 HU L/g, obtained respectively for AuNPs@MnCO3/Mn3O4@PAA-FOA and AuNPs@MnCO3/Mn3O4@PAA-FOA (PI)load. (iii) The intracellular delivery shown by the cytometry and fluorescence results. (iv) The anticancer activity supported by effect of Doxloaded-system on the growth of tumors. (v) The biodistribution in the 4T1 breast tumor-bearing BALB/c mice supported by the elemental analysis of the organs by ICP-OES. (vi) The biocompatibility supported by blood biochemistry and histopathological examinations. The experimental results are presented and discussed to approve the above mentioned supports. © 2021 Elsevier B.V.
Torabi, M. ,
Yaghoobi, F. ,
Karimi shervedani, R. ,
Kefayat, A. ,
Ghahremani, F. ,
Rashidiyan harsini, P. Colloids and Surfaces A: Physicochemical and Engineering Aspects (18734359) 652
Nanocomposite systems, consisting of the reduced graphene oxide/polyacrylic acid as nanocarrier, integrated with folic acid targeting agent and further modified by Deferrioxamine-M (M: Mn2+ or Gd3+) as the diagnostic MRI contrast agents or Temozolomide as a therapeutic agent, abbreviated as (i) GNs@PAA-[DFO-Mn(II)]/FOA, (ii) GNs@PAA-[DFO-Gd(III)]/FOA, and (iii) GNs@PAA-FOA/TMZ, were synthesized, characterized, and examined for B16F10 Melanoma cells through in-vitro/in-vivo methods. Physicochemical characterization of the prepared systems was performed by using DLS, ζ-potential, TEM, FTIR, UV–vis, XPS, fluorescence, and electrochemical methods. The biocompatibility of the nanocarrier was implicated according to the histopathological evaluation of the H&E stained sections of vital organs. Release studies at biological pH 7.4, revealed good stability for TMZ immobilized on the GNs@PAA-FOA/TMZ nanocarrier. The in-vitro MRI studies of the GNs@PAA-[DFO-Mn(II)]/FOA and GNs@PAA-[DFO-Gd(III)]/FOA systems revealed longitudinal relaxivities of 13.00 and 20.64 mM−1 s−1, using variations of the spin-lattice relaxation rates (r1 = 1/T1) as a function of the systems concentrations, respectively. These systems were studied further by the in-vivo method. The obtained images supported their ability for MRI imaging. The intracellular delivery of the system was monitored and supported by flow cytometry based on PI florescent dye loaded onto the introduced nanocarrier, GNs@PAA-FOA/PI. The interaction of the GCE-GNs@PAA-FOA/TMZ, GCE-GNs@PAA-[DFO-Mn(II)]/FOA, and GCE-GNs@PAA-[DFO-Gd(III)]/FOA systems with cancer cells was investigated through electrochemical impedance spectroscopy. The results showed a high affinity of the systems toward B16F10 Melanoma cells with the selectivity degrees of 12.96, 9.92, and 9.62, respectively, compared with L929 cells. © 2022 Elsevier B.V.
Colloids and Surfaces B: Biointerfaces (09277765) 202
An integrated nanocomposite system comprising of manganese oxide (Mn3O4) nanoparticles, functioning as a tumor diagnostic agent, in conjunction with polyacrylic acid (PAA) and ZIF-8, as pH-sensitive drug delivery agents, and methotrexate (MTX), operating as a tumor biomarker and a therapeutic agent (dual mechanism of action), is applied for both diagnostic intentions and controlled delivery of the drug. Physicochemical characteristics of the constructed system, Mn3O4@PAA@ZIF-8/MTX, are investigated by several methods, including X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and electrochemical techniques. The in-vitro magnetic resonance imaging measurements was performed to show the efficiency of Mn3O4@PAA@ZIF-8 nanocomposite as a contrast agent where a relaxivity (r1) of 3.3 mM−1 s−1 is found. The loading ratio was found as 161 % which is four times larger than the value obtained for Mn3O4@PAA system in the same conditions, indicating high capability of the system for MTX delivery. The application of the nanocomposite as a dual pH-sensitive nanocarrier for MTX is studied through in-vitro drug release experiments at pHs of 5.4, 6.8 and 7.4. Interestingly, the results show that a large amount of loaded MTX drug (53 %) is released from the system during incubation and dialysis at pH 5.4, compared with that (20 % and 15 %), respectively, released at pHs 6.8 and 7.4 at the same conditions. The affinity of Mn3O4@PAA@ZIF-8/MTX nanocomposite for capturing of BT-474 and MCF-7 cancer cells was evaluated via impedance spectroscopy measurements. The results show that GC-Mn3O4@PAA@ZIF-8/MTX electrode captures the BT-474 and MCF-7 cancer cells, respectively, by factors of ∼2 and 196 compared with L929 normal cells. This affinity also shows the high selectivity of the system for MCF-7 cancer cells compared with BT-474. © 2021 Elsevier B.V.
Inorganic Chemistry Communications (13877003) 128
Design and construction of a nanocomposite system, containing targeted imaging and therapeutic agents is reported here. The nanoplatform, including AuNPs double coated by MnCO3/Mn3O4 and polyacrylic acid, AuNPs@MnCO3/Mn3O4@PAA (as computerized tomography -scan and magnetic resonance imaging contrast agent), is constructed first. Then, the immobilized polyacrylic acid is conjugated with folic acid, and loaded with doxorubicin and propidium iodide (as targeting, therapeutic, and fluorescence agents), leading to construction of the AuNPs@MnCO3/Mn3O4@PAA-FOA(Dox&PI)load system. Construction and physicochemical behavior of the system are followed by voltammetry, electrochemical impedance spectroscopy, and several surface and solution methods, from which the system is quantitatively characterized. The system performance is supported by the following findings: (i) Amount of loaded drug and loading efficiency, 56.33 and 84.50%, respectively, indicating high capability of the system for doxorubicin delivery. This is one of the important aspects of the current work, which in turn is understood to be related to the large amount of polyacrylic acid as the drug carrier immobilized onto the MnCO3/Mn3O4 nanoparticles. (ii) High ability of the system for capturing of the folate receptor overexpressed 4T1 breast cancer cells, in comparison with L929 normal cells, studied by electrochemical impedance spectroscopy in the presence of [Fe(CN)6]3−/4− redox probe. The large variations of charge transfer resistance against redox reaction of the probe at the GC-Au@MnCO3/Mn3O4@PAA-FOA(Dox)load electrode, after incubation with the 4T1 cells (ΔRct = 217 kΩ, which is ~6 larger than that observed for L929 cells), supports ability of the Au@MnCO3/Mn3O4@PAA-FOA(Dox)load system for effective capturing of 4T1 cells. © 2021 Elsevier B.V.
Journal of Alloys and Compounds (09258388) 886
Supercapacitive performance and electrocatalytic activity of the nickel@nickel oxide core@shells (Ni@NiO), formed with different composition, structure, and morphology via electroless deposition on the surface of carbon black/reduced graphene oxide nanosheets (CB/RGONs) in the presence of citrate ion are reported here. The conditions are controlled and the synthesis is carried out systematically via three different routes: (a) in the absence of CB and citrate ion, (b) just in the presence of CB, and (c) in the presence of both CB and citrate ion. Then, the synthesized composites were transferred onto the GC electrodes, leading to (a) GC-RGONs-PNi@NiO(Particles), (b) GC-RGONs-HENi@NiO(Hedgehog), and (c) GC-CB/RGONs-NPNi@NiO(Nanoprickly) systems, respectively. The synthesis process is followed by several surfaces and electrochemical techniques, from which the physicochemical behaviors of the prepared composites and electrode systems were determined, and the systems were characterized. Then, their activities for capacitive charge storage and electrooxidation of methanol were quantitatively studied. The composite fabricated under optimized conditions, Nanoprickly system, exhibited (i) the most efficient charge storage behavior with specific capacitance (Cs) of 2398 F g−1; and (ii) a large electrocatalytic activity for electrooxidation of methanol with peak current density of 154 A g−1 at 10 mV s−1, compared with values of 1451 & 1049 F g−1 and 72 & 58 A g−1 obtained for the composite ancestors, Hedgehog and Particle systems, respectively. The increase in the Cs and improvement in the electrocatalytic activity of the nanocomposite are attributed to the (i) crucial role of CB nanospacer, preventing graphene layers from restacking, (ii) role of RGONs, dispersing and stabilizing of Ni@NiO nanoprickly particles, and (iii) synergetic chemical coupling effect between NPNi@NiO and CB/RGONs. © 2021 Elsevier B.V.
Sensors and Actuators B: Chemical (09254005) 345
Mixed molecular nanostructures, formed on the surface of gold, provide exceptional assemblies and display unique properties for different purposes, especially, recognition of biomolecules, drug delivery, and cancer cell sensing. In this study, a targeted molecular nanostructure system is prepared on gold, and studied for recognition of cancer cells. The system consists of doxorubicin (Dox), an effective anticancer chemotherapy agent but with cardiotoxicity side effect, and glutamine (Glu), a targeting agent with a potential to reduce the cardiotoxicity induced by Dox, immobilized adjacently on gold via mercaptopropionic acid linker. The preparation process is followed by several surface and solution analysis techniques, and the obtained system is characterized as Au-MPA-(Glu-‖-Dox). The ability of the system to recognize the Human Ovarian Carcinoma (A2780) cells is studied in comparison with Human Caucasian Foetal Foreskin Fibroblast (HFFF2) as nonmalignant cells using electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM) as transaction methods. The system has shown a rapid uptake kinetics (t1/2∼7.7 ± 0.1 min) for A2780 cells. The Au-MPA-(Glu-‖-Dox) system showed high sensitivity in recognition of the A2780 cancer cells (ΔRct of ∼1430 ± 43.0 kΩ and Δf of ∼2500 ± 18 Hz for 5 × 105 cell/mL of A2780 cells). © 2021 Elsevier B.V.
Electrochimica Acta (00134686) 355
Fabrication of active, stable, and cost effective electrocatalysts, as alternative cathodes to Pt or Pt-based materials for catalytic hydrogen production, is important for different industrial purposes, such as hydrogen therapy in medicine, syntheses in pharmaceutical and nutrient, and clean carbon-free energy carrier in industry. Herein, construction, characterization and examination of an efficient electrocatalyst for hydrogen evolution reaction (HER) in alkaline media is reported. The catalyst system is based on nanocomposites formed of urchin-like nickel sulfide incorporated with nickel nanoparticles and nitrogen doped-nanoporous carbon, and decorated electrochemically with ruthenium (IV) oxide on the glassy carbon electrodes, leading to GCE-NiS/Ni/NNPC/RuO2 system. Physicochemical characteristics of the prepared composite systems are studied by several surface, solution and electrochemical methods, from which the system is characterized. Then, electrocatalytic activity of the GCE modified with the composite, is studied for the HER by means of the steady-state linear sweep voltammetry (LSV), polarization curves (Tafel plots), and electrochemical impedance spectroscopy (EIS). The obtained data are analyzed by using appropriate equivalent circuit models, from which the HER kinetics are quantitatively determined. The results revealed that the electrode modified with the prepared composite, GCE-NiS/Ni/NNPC/RuO2, is an efficient electrocatalyst for the HER in alkaline solution, where an overpotential of −82.54 mV at the current density of 20 mA cm‒2 (η20 =− 82.54 mV) with Tafel slope of 49.88 mV dec‒1 is observed. These activities are very close to those obtained on Pt-based electrode materials. The origin of the enhancement in the HER activity can be attributed to (i) the high surface area of the urchin-like structure along with nanoporous carbon, and (ii) the synergistic chemical coupling effects between the NiS, Ni/NNPC and RuO2 nanoparticles. © 2020 Elsevier Ltd
Samiei foroushani, M. ,
Niroumand, N. ,
Karimi shervedani, R. ,
Yaghoobi, F. ,
Kefayat, A. ,
Torabi, M. Bioelectrochemistry (15675394) 130
A multifunctional nanocomposite theranostic system is constructed of manganese oxide (Mn3O4) nanoparticles (NPs), as a tumor diagnostic agent, in conjunction with polyacrylic acid (PAA), as a pH-sensitive drug delivery agent, and methotrexate (MTX), as a model of targeting agent and anticancer drug. Physicochemical characteristics of the Mn3O4@PAA/MTX system is studied in detail by several techniques, including X-ray and Auger photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The system performance is studied based on (i) in-vitro MRI measurements to support efficiency of the Mn3O4@PAA NPs as a diagnostic agent, (ii) drug release performance of the Mn3O4@PAA/MTX NPs at pHs of 5.4 and 7.4 through in-vitro method to evaluate application of the NPs as pH-sensitive nanocarriers for MTX, and (iii) impedance spectroscopy measurements to show Mn3O4@PAA/MTX NPs affinity for capturing of cancer cells. The results show that (i) Mn3O4@PAA NPs can be used as a contrast agent in MRI measurements (r1 ≅ 6.5 mM−1 s−1), (ii) the MTX, loaded on Mn3O4@PAA NPs, is released faster and more efficient at pH 5.4 than 7.4, and (iii) the GC-Mn3O4@PAA/MTX electrode system captures the 4T1 cells 3.32 times larger than L929 cells. © 2019
Electrochimica Acta (00134686) 327
Owing to the growing significance of hydrogen as a non-polluting fuel, design and construction of low-cost, efficient and highly stable electrocatalysts are required for its production by means of water electrolysis. Herein, a general strategy is introduced to fabricate a new type of electrocatalysts based on bimetallic core@shell structure formed on nitrogen-doped nanoporous carbon for electrocatalytic hydrogen evolution reaction (HER). Accordingly, a nickel metal organic framework, Ni‒MOF, synthesized by using benzene-1,3,5-tricarboxylic acid (H3BTC) as the carbon source and 2-methyl-imidazole as the carbon and nitrogen source, is employed, and the nickel/nitrogen−doped nanoporous carbon composite, Ni/NNPC system, is synthesized by the direct carbonization of Ni‒MOF system, i.e. annealing the system in argon atmosphere without using any carbon precursor additive. Then, the outer layers of nickel in Ni/NNPC system are replaced by Pt via galvanic reaction to synthesize the nanostructured system, Ni metal core@Pt thin layer shell, Ni@Pt/NNPC. The step-by-step synthesis of the system and formation of core@shell was supported by several surface analysis techniques. The fabricated materials were transferred onto a glassy carbon (GC) electrode and studied for the HER. The electrochemical results revealed a large electrocatalytic activity for the GCE/Ni@Pt/NNPC system toward the HER in both alkaline and acidic media, compared with GCE, GCE/Ni−MOF and GCE/Ni/NNPC. Tafel slopes of 43.78 and 46.73 mV dec−1, and overpotentials of −33.80 and −76.32 mV (vs RHE) at 20 mA cm−2 (η20) were observed on GCE/Ni@Pt/NNPC electrode in the alkaline and acidic media, under the same conditions, respectively. The observed activity is attributed to (i) the increased electrochemically active surface area, (ii) the cooperative action or synergistic effect between the Pt thin layer shell and the Ni metal core as well as between the Ni@Pt nanoparticles and the NNPC platform, and (iii) effective pore structures of the Ni@Pt/NNPC system. © 2019 Elsevier Ltd
Samiei foroushani, M. ,
Karimi shervedani, R. ,
Kefayat, A. ,
Torabi, M. ,
Ghahremani, F. ,
Yaghoobi, F. Journal of Drug Delivery Science and Technology (17732247) 54
Targeted drug delivery can improve the efficiency of therapeutic and diagnostic agents and reduce their toxicity in cancer treatments. Herein, a theranostic system based on graphene oxide (GO) integrated with polydopamine (PDA), bovine serum albumin (BSA), DTPA-Mn(II) contrast agent, folic acid (FOA) targeting agent, and 5-fluorouracil (5Fu) anticancer drug is constructed to target CT-26 colon cancer cells via folate receptors (FRs) overexpressed on cancer cells. Physicochemical characteristics of the RGO-PDA-BSA/FOA-DTPA-Mn(II)/5Fu system are studied by electrochemical and UV–Vis methods. The system was studied based on (i) in-vitro and in-vivo MRI measurements to verify its efficiency as a diagnostic agent, (ii) histopathological experiments to evaluate biocompatibility of the system, (iii) ICP-OES analysis in conjunction with histopathological tests to find its biodistribution, and (iv) in-vivo experiments using CT-26 colon cells (tumoral animals) to show its ability for cancer therapy. The results show that the RGO-PDA-BSA/FOA-DTPA-Mn(II) is (i) highly promising as a contrast agent for MRI measurements (r1 ≅ 14.7 mM−1 s−1), (ii) biocompatible, (iii) selectively distributed into the CT-26 tumors compared with liver and spleen, and (iv) very effective for therapy of the colon tumors. © 2019 Elsevier B.V.
Journal of Physical Chemistry C (19327447) 123(49)pp. 29932-29945
Physicochemical properties of the nanostructured complex systems, formed between the deferrioxamine B (DFO) siderophore ligand and Zr(IV), Hf(IV), or Fe(III) metal ions at the gold-thiol electrode surface, are determined by different surface, electrochemical, and solution techniques, and the systems are characterized. The results obtained from separate experiments show that the DFO can accumulate and complex the M ions [M: Fe(III), Hf(IV), or Zr(IV)] on the gold-mercaptopropionic acid (Au-MPA) surface efficiently but with different affinities as Zr(IV) > Hf(IV) > Fe(III), leading to different surface morphologies and organizations, and structural diversity of the Au-MPA-DFO-M complexes as Fe(III) > Hf(IV) > Zr(IV). Furthermore, the Fe(III) ions of the Au-MPA-DFO-Fe(III) surface are replaced rapidly by both Hf(IV) and Zr(IV) ions but with different kinetics; the replacement of Zr(IV) is ∼three times faster than that of Hf(IV) at highly acidic solution. Thus, the DFO can be used to identify and differentiate the behaviors of these important heavy metal ions. To our knowledge, this is one of the few cases in which Hf(IV) and Zr(IV) ions show different behaviors. The results of this study are important and can improve our physicochemical insights into the behavior of these ions in conjunction with siderophores, regarding the natural and industrial environments, metal refinery and nuclear power plants, human biological systems, soil contamination, agricultural products, and foods. © 2019 American Chemical Society.
Yaghoobi, F. ,
Karimi shervedani, R. ,
Torabi, M. ,
Kefayat, A. ,
Ghahremani, F. ,
Farzadniya, A. Colloids and Surfaces A: Physicochemical and Engineering Aspects (18734359) 583
Synthesis, characterization, and in-vitro/in-vivo examinations of a theranostic system with novel formulation and straightforward synthesis method are reported in this work. Deferrioxamine-manganese(II), as a theranostic complex (Deferrioxamine as therapeutic and manganese(II) as MRI imaging agent) is conjugated in adjacent to folic acid with the PEGylated gold nanoparticles, leading to formation of biodegradable and biocompatible AuNPs-PEG-[DFO-Mn(II)]‖-[FOA] system. The fabrication process is followed by several characterization methods including TEM, DLS, ζ-potential, FTIR, XPS, UV–vis, and fluorescence. Initially, the characterized system was tested as a contrast agent by MRI and X-ray CT-scan techniques. The values obtained for relaxation rate and the slope of Hounsfield unit vs. concentration, 12.0 mM−1 s−1 and 8.27 HU L/g, supported efficiency of the system for dual imaging applications. In addition, an obvious T1-weighed contrast was observed by in-vivo method. The intracellular delivery of the system was monitored by flow cytometry and florescence microscopy imaging based on PI florescent dye attached to the AuNPs as AuNPs-PEG-[PI]‖-[FOA]. Then, anticancer activity of the system was evaluated by in-vivo experiments carried out on the 4T1 breast tumor-bearing BALB/c mice. Biodistribution of the system was assessed by ICP-OES measurements, indicating effective accumulation of the system in breast tumors. Further experiments exhibited that the growth and metastasis of tumor were significantly inhibited by the system, which in turn, was found to be correlated with therapeutic effect of DFO. Besides abovementioned interesting aspects, this is the first report explaining the dual effects of DFO; (i) complexing capability for contrast agents and (ii) therapeutic effect for 4T1 cancer cells. Finally, biocompatibility of the system was confirmed by blood biochemistry and histopathological evaluations. © 2019 Elsevier B.V.
Biosensors and Bioelectronics (18734235) 117pp. 794-801
Construction of hybrid systems that combine the cancer treatment and diagnosis agents on a single platform, known as theranostic systems, have received great attentions in the field of nanobiomedicine. Here, construction and characterization of a new multifunctional hybrid theranostic system based on RGO, PDA, BSA, DTPA-Mn(II), and MTX constituents, is presented. Accordingly, GO is partially reduced and simultaneously functionalized by dopamine, leading to reduced graphene oxide/polydopamine, RGO-PDA system; and then, the bovine serum albumin protein (BSA) is grafted onto this system. The obtained system, RGO-PDA-BSA, is further decorated with diethylenetriaminepentaacetic acid-Mn(II) as diagnostic system and methotrexate as anticancer drug. Physicochemical characteristics of the RGO-PDA-BSA-DTPA-Mn(II)/MTX system are studied by Fourier transform infrared spectroscopy, atomic force microscopy, and electrochemical methods. The capturing ability of the prepared system for the cancer cells is evaluated through electrochemical impedance spectroscopy (EIS) and by using the 4T1 cancer cells in comparison with L929 normal cells. The EIS results indicate that a degree of selectivity as 6.23 for GC-RGO-PDA-BSA-DTPA-Mn(II)/MTX electrode system toward 4T1 cells, which is larger than that obtained for this system toward the L929 cells. Similar analysis performed using the GC-RGO-PDA-DTPA-Mn(II)/MTX system (having no BSA) indicate that the selectivity degree of the system is increased only by a factor of 1.6, implying that presence of BSA has increased the selectivity of the system for 4T1 cells by a factor of four. This behavior supports the crucial role of BSA in this process for 4T1 cells. Finally, the drug release study of RGO-PDA-BSA-DTPA-Mn(II)/MTX system is performed successfully at pH 7.4. © 2018 Elsevier B.V.
Bioelectrochemistry (15675394) 122pp. 149-157
A new strategy is developed for construction of the mixed molecular nanostructures from folic acid (FOA), a targeting agent, and deferrioxamoine-Ga(III), (DFO-Ga(III)), a theranostic agent, on gold-mercaptopropionic acid surface, Au-MPA. The strategy is focused to achieve a system in which all the active constituents of FOA; i.e., pteridine rings, p-aminobenzoeic acid, and the glutamic acid, having high affinity for folate receptor overexpressed on cancer cells; remain unreacted in adjacent to DFO-Ga(III), Au-MPA-[DFO-Ga(III)]‖-[FOA]. For this purpose, the –NH2 groups of FOA and DFO-Ga(III) were attached covalently and separately to –COOH of Au-MPA surface allowing all the active groups of FOA to be available for drug delivery purposes. The data obtained through several electrochemical and surface analysis techniques, supported successful construction of the designed mixed molecular nanostructures system. In addition, the results showed that the system is stable, and Ga(III) ion does not leave DFO-Ga(III) complex. The prepared surface was successfully tested for capturing of the breast cancer cells 4 T1 as a model. The measurements showed a rapid uptake kinetics (t1/2 of ~6.0 min) and efficient accessibility of the system by the cancer cells; the Rct was significantly increased in the presence of 4 T1 cells compared with blank PBS (ΔRct ~420 kΩ). © 2018 Elsevier B.V.
Electrochimica Acta (00134686) 290pp. 616-625
Porous graphene nanoribbons are synthesized via an effective and template-free method based on introducing of carbon black (CB) into the graphene oxide (GO) layers, and then, thermal exfoliation under hydrogen plasma (H2) stream (PGNRs/CB). The nanocomposites are transferred onto the glassy carbon electrode surface (GCE) and tested directly for charge storage intentions or further modified with Pt-Ru alloy nanoclusters and examined for electrooxidation of methanol. The physicochemical characteristics and electrochemical activities of composites are studied by several surface techniques and electrochemical methods. A remarkable specific capacitance (223.0 F g−1 at 1.0 A g−1) is achieved for PGNRs/CB electrode, compared with 137.2 and 67.6 F g−1 values obtained for porous graphene nanoribbons (PGNRs) and graphene nanosheets (GNs-Ar) formed in the presence of H2 plasma and pure argon streams, respectively. The capacitance retention remained at more than 91% even after 5000 cycles. The supercapacitive behavior and excellent durability achieved for PGNRs/CB materials are attributed to the (i) large surface area of PGNRs obtained by annealing in H2 plasma, and thus, the increased ion accessibility of graphene system, and (ii) stability against the restacking of the PGNRs achieved in the presence of CB. In addition, the GCE-PGNRs/CB was successfully used as a favorable support and further modified with Pt-Ru alloy nanoclusters via electrodeposition. The GCE-PGNRs/CB/Pt-Ru showed an excellent electrocatalytic activity, high resistance against poisoning effect of CO and good stability toward oxidation of methanol. The experimental results are presented and discussed, regarding charge storage and electrocatalytic oxidation of methanol. © 2018 Elsevier Ltd
Karimi shervedani, R. ,
Mirhosseini, H. ,
Samiei foroushani, M. ,
Torabi, M. ,
Rahnemaye rahsepar, F. ,
Norouzi barough, L. Bioelectrochemistry (15675394) 119pp. 1-9
Immobilization of methotrexate (MTX) anticancer drug onto the graphene surface is reported through three methods, including either covalent linkage via (a) EDC/NHS organic activators and (b) electrografting of MTX diazonium salt, or (c) noncovalent bonding, resulting in three different systems. To evaluate the interaction ability of the immobilized MTX with biological species, calf thymus DNA (ctDNA), mouse 4T1 breast tumor, and Human foreskin fibroblast (hFF) cells as models of the primary intracellular target of anticancer drugs, cancer and normal cells, respectively, are examined. The features of the constructed systems and their interactions with ctDNA are followed by surface analysis techniques and electrochemical methods. The results indicate that (i) the amount of the immobilized MTX on the graphene surface is affected by type of the immobilization method; and a maximum value of (Γ = 9.3 ± 0.9 pmol cm−2) is found via electrografting method, (ii) graphene-modified-MTX has high affinity for ctDNA in a wide dynamic range of concentrations, and (iii) the nature of the interaction is of electrostatic and/or hydrogen bonding type, formed most probably between O–H, N–H and C[dbnd]O groups of MTX and different DNA functions. Finally, electrochemical impedance spectroscopy results approved the high affinity of the systems for 4T1 cancer cells. © 2017 Elsevier B.V.
Journal of Physical Chemistry C (19327447) 122(31)pp. 17621-17631
The development of nanocomposites with high activity and stability to generate hydrogen as a green fuel is an interesting challenge for several industrial requirements. Here, ternary alloy nanoparticles of NiCoMo are fabricated electrochemically on graphene nanosheets (GNs) as new nanocomposites using a glassy carbon electrode (GC) base, and then the prepared electrode systems are decorated with ruthenium nanoparticles (Ru NPs). The electrodes are characterized by several surface analysis techniques. The electrocatalytic activity of the electrodes is monitored toward the hydrogen evolution reaction (HER) in alkaline solutions, and the fabrication conditions are optimized systematically based on advanced optimization methods such as central composite design (CCD) and simplex-lattice mixture design (SLMD). Initially, the electrodeposition bath parameters are investigated and optimized by CCD. Then, the SLMD analysis is utilized to obtain the optimal mole ratio of metal ions using HER kinetic data. The results revealed an optimized mole ratio of 33:27:40 for metal ions of Ni/Co/Mo in the electrodeposition bath leading to a GC-GNs-Ni0.20Co0.36Mo0.44 electrode structure. A Tafel slope of -45 mV dec-1, j0 of 1.26 mA cm-2, and η50 of -82 mV are obtained at the optimized structure, which are close to -42 mV dec-1, 5.93 mA cm-2, and -48 mV obtained under the same conditions on the GC electrode modified with commercial Pt/C (GC-Pt/C). The electrode is further decorated with Ru NPs through electrodeposition to form GC-GNs-Ni0.15Co0.31Mo0.38/Ru0.16. The results obtained on this electrode showed high physical and electrochemical stabilities and excellent kinetic performance for the HER, Tafel slope of -38 mV dec-1, j0 of 6.31 mA cm-2, and η50 of -49 mV, which are similar or even better than the results obtained on the GC-Pt/C electrode. © 2018 American Chemical Society.
Electrochimica Acta (00134686) 244pp. 230-238
Non-precious metal electrocatalysts with high activity towards hydrogen evolution reaction (HER) are desirable regarding renewable energy devices such as fuel cells and water electrolysis. However, fabrication of new materials for this purpose remains a main challenge. Here, a binder-free nanocomposite, prickly nickel nanostructured/reduced graphene oxide nanosheets, is constructed via electroless-deposition on cupper surface covered with a fresh prelayer of nickel (Cu-Nifpl-PNiNS/RGONs) for the first time. Then, the fabricated system is tested successfully for the HER in alkaline solutions. Structure and activity of the composite are characterized quantitatively by surface techniques and electrochemical methods. The results show that the hedgehog-like prickly nickel nanostructures wrapped in the RGONs cloth are formed, pinning the PNiNS/RGONs into the Cu-Nifpl surface, resulting in exceptional stability and activity for the Cu-Nifpl-PNiNS/RGONs system. In effect, the composite has shown excellent structural stability against disintegration by ultrasound waves; and electrocatalytic activity towards the HER as η20 = −57 mV, Tafel slope = −43 mV dec−1 and j0 = 1.05 mA cm−2, quite close to −22 mV, −40 mV dec−1 and 5.88 mA cm−2, obtained in the same conditions for commercial Pt/C, respectively. The remarkable increase in electrocatalytic activity was found to be originated partially from increase in the surface roughness and mainly from synergetic chemical coupling effects between PNiNS and RGONs. © 2017 Elsevier Ltd
Electroanalysis (15214109) 29(1)pp. 272-279
A simple, stable and recoverable sensor is developed based on selective and covalent immobilization of dopamine (DA) on the gold (Au) electrode modified by mercaptopropionic acid (MPA) self-assembled monolayers and then, activated with 1-ethyl-3(3-(dimethylamino)propyl)-carbodiimide hydrochloride (EDC)/n-hydroxysuccinimide (NHS) activators. Fabrication steps and analytical application of this modified electrode toward quantitative determination of DA in the presence of ascorbic and uric acids are verified by cyclic and differential pulse voltammetry (CV and DPV) methods in the absence of any redox probe. The oxidation peak current of adsorbed DA changed linearly with the concentration of DA in the range of 0.5 to 600.0 μM with a detection limit of 0.064 μM, and the RSDs varied from 1.4 to 3.5 % for n=3 at each point. Finally, the fabricated sensor is used successfully for electroanalytical determination of DA in human blood plasma and pharmaceutical injection real samples. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Electrochimica Acta (00134686) 187pp. 646-654
Comparative electrochemical behavior of three types of proteins; cytochrome c (Cyt c), Agaricus Bisporus laccase (LacAB) and glucose oxidase (GOx) immobilized on gold mercaptopropionic acid self-assembled monolayer via three different methods, including (a) covalent attachment by using EDC/NHS organic activators, (b) electrostatic interactions, and (c) covalent-coordinate binding by using Zr(IV) ion glue is investigated. Immobilization steps and electrochemical behavior of the immobilized proteins are traced by means of cyclic and differential pulse voltammetry (CV and DPV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results indicate that characteristics of the immobilized systems including; surface coverage, electrocatalytic activity and stability of the proteins are considerably affected by type of the bond formed between electrode and protein (the immobilization method), and nature of the protein. Immobilization via Zr(IV) ion resulted in higher activities for metalloproteins, i.e. Cytc with Heme active center and LacAB with T copper active center, while EDC/NHS method was more efficient for GOx having FAD cofactor. The experimental data will be presented and discussed from which the efficient immobilizing method for each case is introduced. © 2015 Elsevier Ltd. All rights reserved.
Electroanalysis (15214109) 28(4)pp. 874-880
5-amino-1,10-phenanthroline-Fe(II) complex is immobilized onto GC electrode and used for determination of DNA bases. Modifications are traced by electrochemical methods. All DNA bases are electroactive on the modified electrode. The Ips increased linearly with increase of DNA bases concentration. A wide response range was observed for each base (~4 orders for guanine (GA) and adenine (A); and ~2.5 orders for thymine (T) and cytosine (C)) with DLs of 0.15, 4.44, 133.0 and 230.0nM, respectively. The electrode was applied for determination of calf-thymus DNA bases. The value obtained for [(GA+C)/(A+T)], 0.78, is in good agreement with standard value, 0.77. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Electroanalysis (15214109) 28(9)pp. 1957-1969
Electrocatalytic activities of graphene nanosheets/Nile blue nanocomposite, synthesized and adsorbed simultaneously on the glassy carbon (GC−GNs−NB) electrode, are investigated. The nanocomposite was characterized by ATR−FTIR, FESEM and voltammetry. Activity of the electrode toward reduction of H2O2 and oxidation of NO2 − was studied electrochemically. Values of 1.95 and 0.730 mM are found for the Michaelis−Menten constant of the electrode toward H2O2 and NO2 −, respectively. Wide dynamic response ranges were observed for the electrode, with DLs of 0.22 μM H2O2 and 1.1 μM NO2 −. Effect of interferences was studied. The sensor was successfully tested for H2O2 and NO2 − contents in real samples, respectively. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Talanta (00399140) 149pp. 194-201
Selective and sensitive determination of Ga(III) in the presence of Fe(III), as the main interfering ion is studied by using glassy carbon electrode modified with deferrioxamine B (GC-DFO). Characterization and analytical application are performed by different methods including cyclic and differential pulse voltammetry (CV and DPV), electrochemical impedance spectroscopy (EIS), and Field Emission Scanning Electron Microscopy (FESEM). The DPV measurements showed two reduction peaks around -0.630 and -0.830 V. While the current of both peaks varied linearly with Ga(III) concentration of the accumulation solution, the latter was more sensitive and used for construction of the calibration curve. The experimental parameters are studied and optimized. A dynamic calibration curve (6.0×10-11 to 1.4×10-9 mol L-1), including a linear part, from 6.0×10-11 to 1.0×10-9 mol L-1 with mean RSDs of 5.3% for n=3 at 4.0×10-10 mol L-1 Ga(III), and a detection limit of 2.0×10-11 mol L-1 Ga(III) is observed at the optimized conditions. The validity of the method and applicability of the sensor are successfully tested by determining of Ga(III) in natural (river) waters, rice and coal samples. The experimental data are presented and discussed from which the new sensor is characterized. © 2015 Elsevier B.V. All rights reserved.
Biosensors and Bioelectronics (18734235) 77pp. 478-485
Thionine (Th) diazonium cation is covalently attached onto the glassy carbon (GC) electrode via graphene nanosheets (GNs) (GC-GNs-Th). The GC-GNs-Th electrode is subjected to further modifications to fabricate (i) glucose and (ii) nitrite sensors. Further modifications include: (i) direct immobilization of glucose oxidase (GOx) and (ii) electrodeposition of gold dendrite-like nanostructures (DGNs) on the GC-GNs-Th surface, constructing GC-GNs-Th-GOx and GC-GNs-Th-DGNs modified electrodes, respectively. The GC-GNs-Th-GOx biosensor exhibited a linear response range to glucose, from 0.5 to 6.0mM, with a limit of detection (LOD) of 9.6μM and high sensitivity of 43.2μAcm-2mM-1. Also, the GC-GNs-Th-DGNs sensor showed a wide dynamic response range for NO2- ion with two linear parts, from 0.05μM to 1.0μM and 30.0μM to 1.0mM, a sensitivity of 263.2μAmM-1 and a LOD of 0.01μM. Applicability of the modified electrodes was successfully tested by determination of glucose in human blood serum and nitrite in water based on addition/recovery tests. © 2015 Elsevier B.V.
Journal of Physical Chemistry C (19327447) 120(40)pp. 23212-23220
The folic acid-deferrioxamine B-gallium(III) system was assembled on the gold-mercaptopropionic acid surface through an effective method for the first time; then, the assembled nanobioconjugated system, Au-MPA-FOA-DFO-Ga(III), was successfully tested for capturing of the mouse breast cancer cells 4T1. Physicochemical characteristics of the constructed system were studied by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, cyclic and differential pulse voltammetry, and electrochemical impedance spectroscopy (EIS). To evaluate the capturing ability of the folate receptor (FR) expressed cancer cells by the prepared system, the 4T1 cells were tested as a model of FR-expressed cells, and the human foreskin fibroblast cells were tested as a model of no FR-expressed cells. The presence of cancer cells on the system surface was successfully detected by EIS based on variations of the charge-transfer resistance (Rct) of the [Fe(CN)6]3-/4- redox probe at the Au-MPA-FOA-DFO-Ga(III) electrode system/solution interface. Large variations observed in the Rct of the electrode, from 30.26 ± 0.04 to 227.50 ± 0.02 kΩ, supported the high affinity of the Au-MPA-FOA-DFO-Ga(III) system for 4T1 cells. Accumulation of the 4T1 cells onto the system surface was found to be time-dependent. The modified electrode exhibited rapid uptake kinetics for 4T1 cells with a t1/2 of ∼8.5 min. The experimental results are presented and discussed in this paper. © 2016 American Chemical Society.
International Journal of Hydrogen Energy (03603199) 41(31)pp. 13459-13468
Well-dispersed Pt nanoparticles supported on Nile blue functionalized graphene nanosheets were successfully prepared on glassy carbon (GC-GNs-NB-Pt) electrode by a facile and effective two-step electrochemical method. Further electrode was fabricated where NB was formed and attached onto the surface in its polymer form (GC-GNs-NBpoly-Pt). The Pt decorated GNs-NB nanostructures were characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray diffraction (EDX) microanalysis, Raman spectroscopy and electrochemical methods. The results showed a three-dimensional nanostructure for Pt nanoparticles decorated onto the functionalized GNs-NB surface. The characterized electrodes were tested for electrochemical oxidation of methanol in H2SO4. A comparison between the synthesized electrodes; GC-GNs-Pt, GC-GNs-NB-Pt and GC-GNs-NBpoly-Pt, in terms of their electrochemical performance, revealed that the GC-GNs-NB-Pt benefits of a large and exceptional electrocatalytic activity for methanol oxidation. This improved activity could be attributed to the NB playing a crucial role in dispersing and stabilizing of Pt on GNs-NB platform. © 2016 Hydrogen Energy Publications LLC
Electrochimica Acta (00134686) 164pp. 344-352
Abstract A novel method is developed for selective electrochemical detection of guanine (GA) based on activity of gold mercaptopropionic acid self-assembled monolayers (Au-MPA SAMs) functionalized via covalent binding of 5-amino-1,10-phenanthroline-Fe(II) complex (5Aphen-Fe(II)). Modification of the electrode and its activity for oxidation of GA are investigated using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The voltammetric results are supported by the EIS findings. All the results indicate that modification of the Au-MPA SAM electrode surface with 5Aphen-Fe(II) assemblies results in amplification of guanine (GA) oxidation compared with Au and Au-MPA electrodes. The oxidation potential of GA is shifted 0.130 V to more facile (negative) direction compared with the previously studied electrodes for this case. The Au-MPA-5Aphen-Fe(II) electrode shows a wide dynamic range of response (1.0 to 136.0 μM GA), including a linear range (1.0 to 100.0 μM GA) with RSDs varied from 2.1% to 4.2% for n = 4 at each point, and a detection limit of 0.17(±0.01) μM GA. The results show the sensor benefits of a very good stability, repeatability, and excellent selectivity. The GA is determined in the presence of various inorganic ions and biological species especially adenine. A calf thymus double strand DNA sample is successfully tested. © 2015 Elsevier Ltd. All rights reserved.
Electrochimica Acta (00134686) 180pp. 722-736
Oxinate-aluminum nanostructures constructed on gold-mercaptopropionic acid using 5-Amino-8-hydroxyquinoline complex of aluminum(III), Au-MPA-5A8HQ-Al(III), are prepared for the first time via in-situ and ex-situ approaches, and their physiochemical characteristics are studied by cyclic and differential pulse voltammetry, electrochemical impedance spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The electrochemical signal background observed for the in-situ prepared nanostructures is large and superimposed by some faradaic effects, while, it is small, smooth, and featureless for the ex-situ prepared nanostructures. To find the source of these features, effects of several parameters (like solvent, preparation method, and linking spacer between the complex and Au surface) are studied. These features are attributed to the intercalation and physical adsorption of the free 5A8HQ molecules onto the Au-MPA-5A8HQ structure when prepared via in-situ method. Nanostructures with minimum backgrounds in their electrochemical responses could be obtained via in-situ assembling of 5A8HQ from DMF solvent onto the Au-MPA surface, and then, accumulation of Al(III) onto the 5A8HQ layer, and also via ex-situ formation of 5A8HQ:Al(III) complex in the ethanol phase first, and then, transferring the complex onto the Au-MPA surface. The equilibrium constants for the intercalation and adsorption processes are calculated for the first time based on the collected experimental surface quantities. © 2015 Elsevier Ltd. All rights reserved.
Electrochimica Acta (00134686) 173pp. 354-363
Abstract Nile blue/graphene (NB-GNs) nanocomposite was synthesized for the first time via a green and effective one-step electrochemical method, allowing to reduce graphene oxide (GO) and NB on the glassy carbon electrode (GCE) simultaneously and construct GCE-GNs-NBpoly composite. The composite was characterized by scanning electron microscopy (SEM), UV-Vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical results obtained in the absence of any redox probe, where NB was active, allowed to trace step-by-step addition of the NB-GNs nanocomposite onto the GCE electrode surface, supporting formation of the GCE-GNs-NBpoly composite. The electrocatalytic activity of the as-prepared GCE-GNs-NBpoly towards O2 reduction was studied in neutral medium. The results revealed excellent electrocatalytic performance for two-electron reduction of oxygen, suggesting its potential application as metal-free electrocatalysts for O2 reduction reaction. Application of the GCE-GNs-NBpoly in electrochemical biosensing was demonstrated by immobilization of glucose oxidase (GOx) on the surface of GCE-GNs-NBpoly, and then, using it for sensing of glucose. The biosensor exhibited a linear response, from 0.2 to 2.0 mM glucose, with a low detection limit, 2.1 μM, and high sensitivity, 67.0 μA mM-1 cm-2, obtained by cyclic voltammetry method. The proposed biosensor was successfully tested for determination of glucose in blood serum samples. © 2015 Elsevier Ltd.
Carbon (00086223) 93pp. 762-773
We develop an efficient electrocatalyst for hydrogen evolution reaction (HER) based on sulfur doped graphene nanosheets (S-GNs) synthesized with simple, cost effective and scalable method. The structure and morphological characteristics of the fabricated catalysts are investigated by field emission scanning electron microscopy, energy dispersive X-ray diffraction microanalysis, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and electrochemical methods such as voltammetry and impedance spectroscopy (EIS). Electrochemical results show that glassy carbon modified S-GNs heat-treated at 1000°C (GCE-S-GNs-1000) benefit of a good activity toward HER compared to GNs. To improve the characteristics of S-GNs and prevent agglomeration of the layers, the GCE-S-GNs-1000-CB-Ru is fabricated by insertion of carbon black (CB) into S-GNs-1000, and further modification of GCE-S-GNs-1000-CB with ruthenium nanoparticles. The GCE-S-GNs-1000-CB-Ru demonstrated excellent performance for the HER, compared with its ancestors GCE-GNs-1000, GCE-GNs-1000-CB, GCE-S-GNs-1000, GCE-S-GNs-1000-CB as well as with traditional catalysts such as WS2 and MOS2. Analysis of the results obtained by the EIS showed that the increase in the activity of the electrode was partially originated from increase in the double layer capacitance (surface roughness effect) and mostly from increase in the intrinsic activity (synergistic effect). © 2015 Elsevier Ltd. All rights reserved.
Electrochimica Acta (00134686) 142pp. 51-60
Sulfur doped graphene nanosheets (S-GNs) are synthesized by using graphene oxide (GO) as carbon source and sodium polysulfide as sulfur source, and then, annealing the prepared precursors (S-GO) at different temperatures up to 1000 °C. The structure and morphological characteristics of the fabricated composites are investigated by Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Electrochemical results show that S-GNs has high catalytic activity toward oxygen reduction reaction (ORR) in an alkaline electrolyte in comparison with GNs. To improve the characteristics of S-GNs and prevent agglomeration of the particles, the S-GNs-1000-CB is fabricated by mixing the S-GNs-1000 with the carbon black (CB). The results show that CB particles inserted between S-GNs layers function as spacers and prevent the restacking of S-GNs during drying, and thus, most probably promote the diffusion of O2 molecules through S-GNs and enhance the ORR rate. The S-GNs-1000-CB composites show excellent electrocatalytic activity in alkaline solutions over all the studied (catalyst) samples. Our findings demonstrate that S-GNs-1000-CB is an appropriate catalyst for ORR in alkaline solutions, and could be a good candidate for replacement of the precious Pt based catalysts for this goal. © 2014 Elsevier Ltd. All rights reserved.
Analytica Chimica Acta (00032670) 825pp. 34-41
Gold electrode surface is modified via covalent attachment of a synthesized thiol functionalized with 8-hydroxyquinoline, p-((8-hydroxyquinoline)azo) benzenethiol (SHQ), for the first time. The behavior of the nanostructured electrode surface (Au-SHQ) is characterized by electrochemical techniques including cyclic and differential pulse voltammetry (CV and DPV), and electrochemical impedance spectroscopy (EIS). The modified surface is stable in a wide range of potentials and pHs. A surface pKa of 6.0±0.1 is obtained for Au-SHQ electrode using surface acid/base titration curves constructed by CV and EIS measurements as a function of pH. These results helped to determine the charge state of the surface as a function of pH. The gold modified electrode surface showed good affinity for sensing the Al(III) ion at pH 5.5. The sensing process is based on (i) accumulation and complex formation between Al(III) from the solution phase and 8HQ function on the Au electrode surface (recognition step) and (ii) monitoring the impedance of the Au-SHQ-Al(III) complex against redox reaction rate of parabenzoquinone (PBQ) (signal transduction step). The PBQ is found to be a more suitable probe for this purpose, after testing several others. Thus, the sensor was tested for quantitative determination of Al(III) from the solution phase. At the optimized conditions, a linear response, from 1.0×10-11 to 1.2×10-5M Al(III) in semi-logarithmic scale, with a detection limit of 8.32×10-12M and mean relative standard deviation of 3.2% for n=3 at 1.0×10-7M Al(III) is obtained. Possible interferences from coexisting cations and anions are also studied. The results show that many ions do not interfere significantly with the sensor response for Al(III). Validity of the method and applicability of the sensor are successfully tested by determination of Al(III) in human blood serum samples. © 2014 Elsevier B.V.
Bioelectrochemistry (15675394) 98pp. 53-63
Direct electrochemistry of cytochrome c (Cyt c) is achieved via Zr(IV) ion as an immobilization matrix to interface Cyt c on gold surface via thiol self-assembled monolayers. Steps of surface modification and electrocatalytic activity of the immobilized Cyt c are followed by voltammetry, impedance spectroscopy, chronoampetrometry, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results indicate that the native structure of Cyt c is conserved during the immobilization process. The immobilization method is rather simple, effective and free of immobilizing activators and reagents. Direct electron transfer rate constant and surface coverage of the immobilized Cyt c are found as 8.62(±1.98) s-1 and 1.15(±0.38)×10-11molcm-2, respectively. Bioactivity studies of the immobilized Cyt c toward oxidation of the ascorbic acid (AA) substrate show a linear response, from 10.0μM to 1.30mM AA, with a detection limit of 5.0(±1.8) μM AA and mean relative standard deviations varied from 13.7% to 3.7% for n=4 at each point. A value of 1.6(±0.8) mM AA is found for the Michaelis-Menten constant of Au-MPA-Zr(IV)-Cyt c toward AA for the first time. The tightly immobilized Cyt c maintains its bioactivity for more than 32days storage at 4°C. © 2014 Elsevier B.V.
Electrochimica Acta (00134686) 121pp. 376-385
A novel and uniform graphene nanosheet-gold nanoparticles (GNs-AuNPs) hybrid has been fabricated from sulfur-modified graphene nanosheets (S-GNs) impregnated with HAuCl4 as Au precursor. Physicochemical and morphological characteristics of the GNs-AuNPs hybrids were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface Raman spectroscopy (SRS), and high resolution transmission electron microscopy (HRTEM). The results of the XRD and HRTEM demonstrated well dispersed Au nanoparticles on GNs with an average particle size of less than 10 nm and a narrow size distribution of 6 to 8 nm. A film of GNs-AuNPs hybrid was constructed on a glassy carbon electrode (GCE) through layer-by-layer (LBL) assembly of 4-aminothiphenol (ATP) on GCE, and then, transferring the hybrid to the sulfur function of ATP to form GCE-ATP-GNs-AuNPs modified surface. Application of the GNs-AuNPs hybrid in electrochemical biosensing was demonstrated by immobilization of glucose oxidase (GOx) as a model on the surface of GCE-ATP-GNs-AuNPs, and then, using it for sensing of glucose. The biosensor exhibited a wide linear response range, from 1.0 to 12.0 mM and 0.1 to 8.0 mM glucose, with a detection limit of 9.3 and 4.1 μM and high sensitivity, 47.6 μA mM-1 cm-2 and 45.0 kΩ/log(Cglucose/mM) obtained by voltammetry and electrochemical impedance spectroscopy (EIS), respectively. According to the results obtained by analysis of the EIS experimental data, the source of enhanced activity was found to be originated from the synergistic effect of GNs and AuNPs, the role of ATP mediating assembling of GNs-AuNPs hybrid on GCE, and the increase in the surface roughness. This work opens up a new and facile way for direct preparation of metal nanoparticles embedded in GNs, which will enable exciting opportunities in advanced applications based on graphene-metal hybrids like electrocatalysis for energy conversion and highly sensitive modifier films for electrochemical sensors and biosensors. © 2014 Elsevier Ltd.
Sensors and Actuators B: Chemical (09254005) 204pp. 783-790
A novel and supersensitive enzyme-free electrochemical glucose sensor fabricated on copper substrate by in situ growing three-dimensional (3D) prickly nickel nanowires (PNNWs) using an electroless strategy is explained for the first time. The surface morphology of PNNWs is characterized by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray diffraction (EDX) microanalysis. Electrochemical performance of the Cu-Ni-PNNWs electrode for sensing of glucose is investigated by cyclic voltammetry and chronoamperometry in alkaline solutions. The Cu-Ni-PNNWs electrode showed a great enhanced electrocatalytic activity toward oxidation of glucose, in comparison with its platform, Cu-Ni, prepared by electrodeposition of Ni on Cu electrode. Under optimized conditions, the sensor showed a linear response in a wide range of glucose concentrations, from 3.0 × 10-6 to 2.0 × 10-3 M, with a large sensitivity (4243 μA cm-2 mM-1) and low detection limit of 0.1 μM. The sensor is 1.5 times more sensitive than the recently reported (2900 μA cm-2 mM -1) for nonenzymatic detection of glucose using porous nickel nanostructures. In addition, the Cu-Ni-PNNWs electrode is successfully tested for determination of glucose in human blood sample. The experimental results revealed a good reproducibility, long-term stability and high selectivity with no interference from other oxidizable species accompanying glucose in matrix of the real samples. © 2014 Elsevier B.V.
Bioelectrochemistry (15675394) 92pp. 27-31
Interaction of uranyl ion (UO22+) with immobilized double strand calf thymus DNA (ds-ct-DNA) on zirconium attached gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) is monitored by electrochemical techniques. The results show that after 15min proximity of the immobilized DNA with UO22+, the peak currents of the square wave voltammograms are decreased (about 80%), and the equivalent circuit model of electrochemical impedance spectroscopy (EIS) data, requires two constant phase elements (CPE) instead of only one. By using the surface concentration of DNA (≈2.3×10-13mol/cm2) and the number of the anthraquinonedisulfonic acid (AQDS) adsorbed on DNA (1.34×10-10mol/cm2) the ration of AQDS per DNA base pairs is obtained ≈1/30 before proximity to UO22+. Based on EIS technique, we find that the double strand structure of immobilized DNA on the electrode surface has been changed (damaged) by UO22+. This modified electrode has potential of becoming a screening tool for the rapid assessment of the interaction and genotoxicity of existing and new chemicals. © 2013 Elsevier B.V.
Biosensors and Bioelectronics (18734235) 39(1)pp. 31-36
Deferrioxamine, a bacterial hydroxamic siderophore having high binding affinity for Fe(III), is used in its immobilized form, as self-assembled monolayer on Au, for accumulation and recognition of Fe(III) from the solution phase. The accumulated Fe(III) is detected via both active mode based on faradaic reduction current of Fe(III), and inactive mode based on impedimetric effect of accumulated Fe(III) against redox reaction of a suitable probe. Appropriate electrochemical techniques, square wave voltammetry and electrochemical impedance spectroscopy, are used for the transduction of analytical signals obtained by this sensor. Then, the parameters influencing the sensor response are optimized. In the best conditions, a linear response, from 1.0×10-10 to 1.0×10-7M Fe(III) in logarithmic scale with a detection limit of 2.0×10-11M, and mean relative standard deviation of 1.7% for n=4 is observed. The results show that the sensor can be used for determination of Fe(III) in the presence of various inorganic ions and biological species. Validity of the method and applicability of the sensor are successfully tested by determination of Fe(III) in various real samples including plant tissue (corn leaves), industrial alloy (Ferrotitanium), and pharmaceutical samples (Venofer® ampoule, Ironorm® capsule, and V.M. Protein® powder). © 2012 Elsevier B.V..
Surface Science (00396028) 616pp. 100-103
In this paper layer-by-layer (LBL) assembly of calf thymus DNA (ct-DNA) onto gold-mercaptopropionic acid self-assembled monolayer via Zr(IV) ion glue, Au-MPA-Zr(IV)-ct-DNA SAM, is monitored by scanning tunneling microscopy (STM) technique. The STM images of Au-MPA-Zr(IV) template show well-organized arrays of rod-like peaks. ct-DNA has been immobilized on the Au-MPA-Zr(IV) surface in hilly forms, implying globular structure for the immobilized ct-DNA. This immobilization strategy offers a simple and fast method to prepare the Au-MPA-Zr(IV)-ct-DNA template with promising applications for immobilization and study of the other compounds. © 2013 Elsevier B.V.
Bioelectrochemistry (15675394) 84pp. 25-31
Direct electrochemistry of a new laccase enzyme immobilized on gold and its application as a biosensor for dopamine (DA) are investigated by voltammetry and electrochemical impedance spectroscopy. The sensor demonstrated a redox adsorption behavior with E 0'=+180mV vs. Ag/AgCl for immobilized Agaricus bisporus laccase (LacAB) enzyme. The MPA platform was assembled on Au with and without utilization of ultrasounds. Excellent results were obtained by using the enzyme electrode fabricated based on MPA assembled with sonication. The LacAB immobilized in this condition showed a large electrocatalytic activity for oxidation of DA. Accordingly, a third-generation (mediator free) biosensor was constructed for DA. The DA concentration could be measured in the linear range of 0.5 to 13.0 and 47.0 to 430.0μmolL -1 with correlation coefficients of 0.999 and 0.989, respectively, and a detection limit of 29.0nmolL -1. The biosensor was successfully tested for determination of DA in human blood plasma and pharmaceutical samples. © 2011 Elsevier B.V.
Sensors and Actuators B: Chemical (09254005) 160(1)pp. 145-153
A simple method is developed for electrochemical detection of DNA sequence. The probe DNA (p-DNA) is immobilized onto Au-MPA SAM electrode modified with zirconium ion, Zr(IV). The electrochemical results imply that immobilization is performed effectively via the phosphate groups with no implication of the p-DNA bases in the immobilization stage, ensuring that the bases of the p-DNA have appropriate alignment to be accessible for hybridization. Layer-by-layer characterization of the electrode is performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN) 6]3- and [Ru(NH3)6]3+ as anionic and cationic non-intercalative redox probes, respectively. Whereas, detection of the hybridization between p-DNA and target DNA (t-DNA) is probed using methylene blue (MB) and anthraquinone disulfonic acid (AQDS) as cationic and anionic intercalators, respectively. The variations of charge transfer resistance are found to be linearly related to the logarithm of the complementary DNA (c-DNA) concentration, from 1.0 × 10-10 to 1.0 × 10-6 M, with a detection limit of 8.5 × 10 -11 M using AQDS. Other merits of the sensor include; good sensitivity, selectivity in detection of c-DNA from mismatch and non-complementary strands, ease switching to different t-DNA detections, and having cheap preparation method. © 2011 Elsevier B.V. All rights reserved.
Journal of Electroanalytical Chemistry (15726657) 660(1)pp. 37-44
Attachment of natural double strand calf thymus DNA onto gold-mercaptopropionic acid self-assembled monolayer electrode via Zr(IV) ion glue, Au-MPA-Zr(IV)-ds-ct-DNA SAM, is studied. The sequential assembly of the layers on the Au surface is traced by electrochemical methods including cyclic and square wave voltammetries in the presence of methylene blue. The results show that DNA is attached to Zr(IV) via its phosphate groups without any contribution from its bases. Effects of the MB concentration on the behavior of adsorbed MB, ionic strength on the MB adsorption, and pH on the amount of immobilized DNA are studied. The proposed method for the preparation of the new template, the Au-MPA-Zr(IV)-ds-ct-DNA, is relatively simple and fast. Long-term stability of this electrode is tested by keeping the template at pH 3, and carrying out a daily electrochemical study at pH 7.4. Under these circumstances, the Au-MPA-Zr(IV)-ds-ct-DNA electrode showed stable behavior for one week. © 2011 Elsevier B.V. All rights reserved.
Journal of Physical Chemistry C (19327447) 115(16)pp. 8042-8055
Nanostructure assemblies based on ferrioxamation of gold-mercaptopropionic acid, Au-MPA-DFO-Fe(III), are prepared via in-situ and ex-situ approaches for the first time and described by cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS) and scanning tunneling microscopy (STM) techniques. The assemblies formed via the two approaches show different structures, topologies, and electrochemical kinetics. The STM images show that the Au-MPA-DFO layer is formed in rodlike arrays with 3-4 nm peak-to-peak distances, while the arrays of the Au-MPA-DFO-Fe(III) layers formed by the in-situ and ex-situ methods, respectively with sharp and round ridges, have similar peak-to-peak distances of 2-3 nm. The CVs reveal that the Fe(III) ion immobilized by the ex-situ method is more stable by 14.48 kJ/mol. The relative amounts of the adsorbed Fe(III) ions via the in-situ and ex-situ methods, ex-situ/in-situ, obtained by CV and EIS are 1.33 ± 0.13 and 1.37 ± 0.19, respectively. Faradaic and impedimetric surface titrations both predict a surface-pKa of ∼9.4 for the Au-MPA-DFO self-assembled monolayer (SAM). © 2011 American Chemical Society.
Electroanalysis (15214109) 22(9)pp. 969-977
A new sensor, gold-6-amino-2-mercaptobenzothiazole (6A2MBT), was fabricated via a self-assembly procedure. Electrochemical properties of the monolayer were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent antifouling property against the oxidation products of DA, allowed us to construct a dynamic calibration curve with two linear parts, 1.00 10-6 to 3.72 10-4 and 3.72 10-4 to 6.42 10-4 M DA, with correlation coefficients of 0.997 and 0.992 and a detection limit of 1.57 10-7 M DA by using differential pulse voltammetry (DPV), respectively. Finally, the performance of the Au-6A2MBT modified electrode was successfully tested for electrochemical detection of DA in a pharmaceutical sample. © 2010 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim.
Bioelectrochemistry (15675394) 77(2)pp. 100-105
An electrochemical biosensor, constructed by immobilization of Zr(IV) on the topside of gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr SAM), is developed for the sensitive quantification of calf thymus DNA (ct-DNA). The sensor is based on ionic adsorption of ct-DNA from its phosphate backbone onto the Au-MPA-Zr(IV) SAM electrode. Preparation, characterization, and application of the sensor for determination of ct-DNA are described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Osteryoung square wave voltammetry (OSWV) in the presence of an appropriate redox reaction probe. Parameters influencing the method have been tested. A linear range calibration curve from 1.0 × 10- 4 to 5.0 × 10- 7 g mL- 1 ct-DNA with a detection limit of 9.5 × 10- 8 g mL- 1 and mean of relative standard deviations (R.S.D) of 2.5% for n = 4 at each point was observed in the best conditions by EIS. Regeneration of the surface was carried out successfully by 5 min sonication in 0.1 M KOH solution and then 1 min incubation in 1.0 × 10- 3 M Zr(IV) with a good reproducibility, R.S.D = 1.5% for n = 4 as detected by EIS. The long-term storage stability of the electrode was also studied. © 2009 Elsevier B.V. All rights reserved.
Sensors and Actuators B: Chemical (09254005) 137(1)pp. 195-204
Comparative electrochemical study of glucose oxidase (GOx) immobilized on gold electrodes modified by three types of mercaptocarboxylic acid self-assembled monolayers (SAMs), including 3-mercaptopropionic acid (MPA), 3-mercaptosuccinic acid (MSA), and thiodisuccinic acid (TDSA), is reported. GOx was immobilized on SAMs via anhydride route to prepare (Au-MPA-GOx), (Au-MSA-GOx), and (Au-TDSA-GOx) biosensors. Steps of formation and analytical performance of the prepared biosensors were traced by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). While partial surface coverage (θ) of gold by thiols showed the following order Au-MPA(θ = 36%) > Au-MSA(θ = 30%) > Au-TDSA(θ = 24%), inverse effect was observed for slopes (activities) of the calibration curves for glucose determination as Au-MPA-GOx < Au-MSA-GOx < Au-TDSA-GOx. This matter was explained based on advantages of multi-branch carboxylic acids (i.e. TDSA) allowing immobilization of more enzymes even with less surface coverage (24%) by thiols. Data obtained by CA and EIS methods for the entire of the study were in good agreement. © 2008 Elsevier B.V. All rights reserved.
Journal Of The Iranian Chemical Society (1735207X) 6(1)pp. 104-112
Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+:Cu2+ or Ag+) for electrocatalytic determination of hydroquinone (H2Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H2Q concentrations were linear from 1.0 × 10-5 to 4.0 × 10-4 M (r=0.998) for Au-5A2MBI, from 1.0 × 10-5 to 6.0 × 10-4 M (r=0.998) for Au-5A2MBI-Cu2+, and from 2.0 × 10-6 to 2.0 × 10-5 M (r=0.996) and 1.0 × 10-4 to 1.0 × 10-3 M (r=0.991) for Au-5A2MBI-Ag+ SAM modified electrode. The respective detection limits were found as 6.5 × 10-6, 4.6 × 10-6 and 1.8 × 10-7 M. Both Cu2+ and Ag+ ions were found to have a good electrocatalytic effect on the oxidation of H2Q; however, Ag+ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag+ SAM electrode was used as a suitable sensor for determination of H2Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.
Sensors and Actuators B: Chemical (09254005) 139(2)pp. 657-664
A new modified electrode is reported for the determination of zirconium ion (Zr(IV)) based on (i) in-situ functionalization of gold cysteamine self-assembled monolayer by nitrilotriacetic acid, and its further modification of by hydroxylamine hydrochloride as a recognition system, and (ii) electrochemical impedance spectroscopy (EIS) as a transduction method. Zr(IV) was selectively accumulated on the topside of hydroxameated surface, and the surface blocked the charge transfer process between metallic base and a redox probe in solution. The EIS complex plane plots showed a drastic change in the charge transfer resistance of the probe redox reaction as a function of Zr(IV) concentration. This behavior was used for construction of the calibration curve, and a linear range from 1.0 × 10-9 to 5.0 × 10-5 M Zr(IV) with a detection limit of 7.8 × 10-10 M and a relative standard deviation (RSD) of 1.79% for n = 5 at 5.0 × 10-5 M Zr(IV) was observed. The validity of the method and applicability of the sensor were successfully tested by determining Zr(IV) in synthetic as well as natural waters (tap and river waters) without interference from sample matrix. © 2009 Elsevier B.V. All rights reserved.
Bioelectrochemistry (15675394) 75(2)pp. 124-129
Immobilization of l-lysine α-oxidase on gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-LOx SAM) electrode is verified experimentally in the present work. Fabrication steps and electrochemical interaction of Au-MPA-LOx with l-lysine were monitored by general electrochemical methods like cyclic voltammetry (CV) and chronoamperometry (CA), and by a more advanced method, electrochemical impedance spectroscopy (EIS) in the presence of parabenzoquinone (PBQ) redox probe. The data was analyzed from which quantitative kinetic parameters were extracted. The results confirmed successful immobilization of LOx, and thus, fabrication of Au-MPA-LOx SAM electrode. Our initial tests revealed a linear response for Au-MPA-LOx SAM electrode toward l-lysine concentration in solution at biological conditions, pH 7.4. The experimental data will be presented and discussed from which the Au-MPA-LOx SAM electrode is characterized, and the kinetic merits of the interface interactions are introduced. © 2009 Elsevier B.V. All rights reserved.
Journal of Electroanalytical Chemistry (15726657) 633(1)pp. 259-263
A new method is established for the electrochemical detection of zirconium ion (Zr(IV)) based on electrochemical impedance spectroscopy transduction method, and hydroxamated gold surface recognition system. The method successfully served for the detection of Zr(IV) with a wide dynamic range of 1.0 × 10-9 to 5.0 × 10-5 mol L-1, and a detection limit in nmol L-1 scale. Construction of the calibration curve by "one-impedance for one-concentration" method developed here helped us to save the experimental time by saving the data acquisition time by a factor of ∼20, and further, eliminating data approximation and parameter extraction times. © 2009 Elsevier B.V. All rights reserved.
Biosensors and Bioelectronics (18734235) 24(7)pp. 2199-2204
Preparation, characterization, and application of a new sensor for the determination of phosphate in blood serum is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and osteryoung square wave voltammetry (OSWV) in the presence of an appropriate redox reaction probe. The sensor was based on ionic adsorption of phosphate on Zr(IV) immobilized on gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) electrode. Parameters influencing the method were optimized. A linear range calibration curve from 1.0 × 10-7 to 1.0 × 10-6 M PO43- with a detection limit of 5.30 × 10-8 M and mean of relative standard deviations (R.S.D.) of 2.75% for n = 4 was observed in the best conditions by OSWV. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for the determination of phosphate in the presence of various ions. Regeneration of the surface was carried out successfully by 5-min sonication in 0.1 M KOH solution and then 1-min incubation in 1.0 × 10-3 M Zr(IV) with a good reproducibility, R.S.D. = 1.47% for n = 4 by OSWV. The validity of the method and applicability of the sensor were successfully tested by detection of phosphate in blood serum after deproteinization of sample without interference from sample matrix. The long-term storage stability of the electrode was studied. The experimental data is presented and discussed from which the new sensor is characterized. © 2008 Elsevier B.V. All rights reserved.
Electrochimica Acta (00134686) 53(12)pp. 4185-4192
Electrocatalytic activity of a new catalyst toward the oxidation reaction of hydroquinone as a model compound is described. The catalyst was formed by immobilizing metal cations on the topside of a gold-5-amino-2-mercaptobenzimidazole, self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+: Cu2+, Ag+) electrode. Preparation steps and the electrocatalytic activity of the catalyst were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS data were approximated by appropriate electronic equivalent circuit models from which kinetic parameters, such as charge transfer resistance, double layer capacitance, and apparent rate constant (kapp), were estimated. Excellent activity was observed for Au-5A2MBI-Ag+ SAM with the following order: Au-5A2MBI-Ag+ > Au-5A2MBI-Cu2+ > Au-5A2MBI, after testing many modified electrodes. The increased activity originates from a modification of the Au-5A2MBI structure by mediating the effect of Ag+. This behavior was understood from significant increases in the kapp without significant changes in the double layer capacitance. © 2008 Elsevier Ltd. All rights reserved.
International Journal of Hydrogen Energy (03603199) 33(10)pp. 2468-2476
Kinetics of hydrogen evolution reaction (HER) was studied in 1 M NaOH at 298 K on nickel-phosphorous-carbon (Ni81 P16 C3) composite electrode. Evaluation of the electrode activities was carried out by steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The kinetic parameters obtained by Tafel curves revealed that Ni-P composites modified by incorporation of carbon from L-lysine source during the electroplating process were active toward the HER. Thus, to study more precisely the electrode activities, the EIS measurements were performed. A surface roughness factor (Rf) more than three orders of magnitude was obtained for the Ni81 P16 C3 electrode. The HER rate constants were estimated using Tafel-impedance data assuming the Volmer-Heyrovský path. Analysis of the Rf in conjunction with the values obtained for rate constantans showed that the increase in activity of the electrode was originated by 18% from increase in Rf and by 82% from increase in the intrinsic activity (synergetic effect). Microstructure and composition of the electrodes were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and elemental microanalysis (EDX). Besides the good electrocatalytic activity, excellent chemical and electrochemical stability was observed for Ni81 P16 C3 composite electrode toward the HER. © 2008 International Association for Hydrogen Energy.
Journal of New Materials for Electrochemical Systems (14802422) 11(4)pp. 259-265
Nickel-phosphorus-codeposited graphite carbon (Ni-P-Cg) materials have been studied by means of electrochemical and mi-crostructural techniques. Steady-state polarization Tafel curves showed that the Ni-P-C electrodes were active toward the HER. The activity of the Ni-P-Cg materials was depended on the electrode composition and the best activity was obtained on Ni 83P12C5 electrode (n250 = -242.4±2.1 mV), which was subjected to annealing at 400 °C in argon atmosphere. EIS measurements revealed that the electrodes were active and the source of the activity was originated mainly from improvement in electronic structure of the catalyst, and partially from increase in the surface roughness caused by the heat treatment process mentioned above. Furthermore, the Volmer-HeyrovsĶý mechanism was determined for the HER and the latter was the rate-determining step. © J. New Mat. Electrochem. Systems.
Electroanalysis (15214109) 20(5)pp. 550-557
Functionalization of gold cysteamine (Au-CA) self-assembled monolayer with 4-formylphenylboronic acid (BA) via Schiff's base formation, through in situ method to fabricate Au-CA-BA electrode is presented and described. The fabricated electrode was used as a novel sensor for accumulation and determination of dopamine (DA). The accumulation of DA as a diol on the topside of Au-CA-BA as a Lewis acid, was performed via esterification (Au-CA-BA-DA), and followed for determination of DA. Functionalization, characterization, and determination steps were probed by electrochemical methods like cyclic voltammetry and electrochemical impedance spectroscopy. The data will be presented and discussed from which a new sensor for DA is introduced. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
Electrochimica Acta (00134686) 53(22)pp. 6293-6303
A new, simple, and easy method for introducing hydroxamic acid group onto the surface of polycrystalline gold electrode by means of in-situ layer-by-layer functionalization is described. The fabrication was performed in a four-step method: (i) modification of gold by cysteamine self-assembled monolayer, Au-CA SAM, (ii) activation of nitrilotriacetic acid (NTA) by 1-ethyl-3(3- (dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS), (iii) immobilization of activated NTA onto Au-CA to form Au-CA-NTA, and (iv) conversion of the remaining activated carboxylic acid groups of Au-CA-NTA (terminals) to hydroxamic acid groups by using hydroxylamine hydrochloride (HAH) to form Au-CA-NDHA modified electrode. The resulting modified electrode was successfully tested for accumulation of zirconium ion (Zr(IV)) from an aqueous acidic solution. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were used to trace the events in each step, characterize the surface, determine the surface pKas, and find the affinity of the prepared electrode towards the Zr(IV). Surface pKas equal to 6.5 and 5.5 were estimated for Au-CA-NTA, and Au-CA-NDHA SAM electrodes, respectively. These values allowed estimating the charge-state of the surface at any pHs. The modified surface showed a large affinity for selective accumulation of Zr(IV) from acidic solution. © 2008 Elsevier Ltd. All rights reserved.
Electrochimica Acta (00134686) 52(24)pp. 7051-7060
Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold-sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-pKa values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au-MBT assembly is different from those of two others and confirms formation of Au-MBT SAM via both sulfur atoms of MBT. © 2007 Elsevier Ltd. All rights reserved.
Journal Of The Iranian Chemical Society (1735207X) 4(2)pp. 221-228
Electrochemical characterization and application of nickel ruthenium dioxide (Ni-RuO2) as a pH sensor for the determination of petroleum oil acid number is described. The sensor consists of RuCl3 thermally decomposed onto the upper side of a polycrystalline nickel electrode at 400°C in an open furnace. The advantages of the sensor are: (i) easy preparation, (ii) fast response in a large pH range, (iii) high physical and chemical stability, and (iv) excellent reproducibility as determined by the reproducible linear variation of charge transfer resistance (Rct) as a function of overpotential (η) obtained by electrochemical impedance spectroscopy (EIS), and the Nernstian slope of the electrode potential in a wide range of pH (1.5-12.5) obtained by potentiometric measurements. The potentiometric selectivity coefficients of the sensor toward some anions and cations were evaluated in aqueous solution. The characterized Ni-RuO2 pH sensor was successfully tested for the determination of petroleum oil acid number.
Sensors and Actuators B: Chemical (09254005) 126(2)pp. 415-423
A new method is developed, for direct coupling of enzymes on gold thiol self-assembled monolayers, based on glucose oxidase as a model enzyme and gold mercaptosuccinic anhydride self-assembled monolayer as a platform. The immobilization method is simple and fast, and enzyme is immobilized very close to the gold electrode surface. Preparation steps and the biosensor response to glucose are monitored by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The relative differences between the slopes and intercepts of the current and conventional methods, using EDC/NHS activators for immobilization, are 10 and 8% for five-time measurements of each calibration curve obtained by chronoamperometry. The EIS data are approximated based on appropriate electronic equivalent circuit models and charge transfer resistances (Rct) are extracted from which a wide range linear calibration curve is obtained using 1/Rct versus glucose concentration. In addition, the analytical method is improved based on the EIS abilities allowing decreasing data acquisition time by a factor of 15. © 2007 Elsevier B.V. All rights reserved.
Journal of Power Sources (03787753) 164(2)pp. 890-895
The steady-state and anodic corrosion of Pb-0.17 wt.% Ca-0.88 wt.% Sn, and Pb-0.17 wt.% Ca-0.88 wt.% Sn-0.06 wt.% Li alloys in 4.5 M H2SO4 at 25 °C were studied using cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. The experimental results show that the lithium added to Pb-Ca-Sn alloy increases corrosion resistance in equilibrium potential and inhibits the growth of the anodic corrosion layer. © 2006 Elsevier B.V. All rights reserved.
Analytica Chimica Acta (00032670) 587(2)pp. 254-262
Electrochemical characterization of gold cysteamine self-assembled monolayer, in situ functionalized with ethylenediaminetetraacetic acid (Au-CA-EDTA SAM), is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Osteryoung square wave voltammetry (OSWV). The results obtained by EIS and CV, in the presence of [Fe(CN)6]3-/4- redox probe, show that EDTA is successfully grafted to the surface of Au-CA electrode. Reproducible and reversible variation of the Rct and ΔEp as a function of solution pH show that Au-CA-EDTA SAM is stable in a wide range of pH and potentials. Accumulation of the Pb2+ and Cu2+ ions on the Au-CA-EDTA SAM electrode is investigated using faradaic currents or impedimetric effects measured by OSWV and EIS, respectively. These results reveal the presence of active complexing functional groups of EDTA on the surface, and thus, the formation of Au-CA-EDTA SAM electrode. The new sensor responds to the Pb2+ and Cu2+ separately and simultaneously in a wide linear range of concentrations. © 2007 Elsevier B.V. All rights reserved.
Electrochimica Acta (00134686) 53(2)pp. 426-433
Ternary nickel-iron-carbon (Ni-Fe-C) alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). The electrochemical efficiency of the electrodes has been evaluated on the basis of electrochemical data obtained from the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in 1 M NaOH solution at 298 K in the absence and presence of cyanide ion as the poison. Steady-state polarization Tafel curves showed that the Ni-Fe-C electrodes were apparently active for the HER. Therefore, the EIS studies were performed to obtain more precise data and find the source of activity. A surface roughness of more than three orders of magnitude was observed for Ni62Fe35C3 electrode. The rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated by using Tafel-impedance data. A comparison between the values obtained for Rf by the EIS and the values obtained for k2 by approximation of Tafel-impedance data revealed that the increase in activity of Ni62Fe35C3 electrode toward the HER was partially (20%) originated from increase in the surface roughness, and mostly (80%) from increase in the intrinsic activity. © 2007 Elsevier Ltd. All rights reserved.
Analytica Chimica Acta (00032670) 601(2)pp. 164-171
Preparation and application of gold 2-mercaptosuccinic acid self-assembled monolayer (Au-MSA SAM) electrode for determination of iron(III) in the presence of iron(II) is described by cyclic voltammetry, electrochemical impedance spectroscopy, and Osteryoung square wave voltammetry. The square wave voltammograms showed a sharp peak around positive potentials +0.250 V that was used for construction of the calibration curve. Parameters influencing the method were optimized. A linear range calibration curve from 1.0 × 10-10 to 6.0 × 10-9 M iron(III) with a detection limit of 3.0 × 10-11 M and relative standard deviation (R.S.D.) of 6.5% for n = 8 at 1.0 × 10-9 M iron(III) was observed in the best conditions. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for determination of iron(III) in the presence of various ions. The validity of the method and applicability of the sensor were successfully tested by determining of iron(III) in natural waters (tap and mineral waters) and in a pharmaceutical sample (Venofer® ampoule) without interference from sample matrix. The experimental data are presented and discussed from which the new sensor is characterized. © 2007 Elsevier B.V. All rights reserved.
Bioelectrochemistry (15675394) 69(2)pp. 201-208
A method is developed for quantitative determination of glucose using electrochemical impedance spectroscopy (EIS). The method is based on immobilized glucose oxidase (GOx) on the topside of gold mercaptopropionic acid self-assembled monolayers (Au-MPA-GOx SAMs) electrode and mediation of electron transfer by parabenzoquinone (PBQ). The PBQ is reduced to hydroquinone (H2Q), which in turn is oxidized at Au electrode in diffusion layer. An increase in the glucose concentration results in an increase in the diffusion current density of the H2Q oxidation, which corresponds to a decrease in the faradaic charge transfer resistance (Rct) obtained from the EIS measurements. Glucose is quantified from linear variation of the sensor response (1/Rct) as a function of glucose concentration in solution. The method is straightforward and nondestructive. The dynamic range for determination of glucose is extended to more than two orders of magnitude. A detection limit of 15.6 μM with a sensitivity of 9.66 × 10- 7 Ω- 1 mM- 1 is obtained. © 2006 Elsevier B.V. All rights reserved.
Talanta (00399140) 69(3)pp. 741-746
Fabrication and application of a voltammetric sensor based on gold 2-mercaptobenzothiazole self-assembled monolayer (Au-MBT SAM) for determination of silver ion is described. Preliminary experiments were performed to characterize the monolayer. The surface pKa determined for the MBT monolayer is 7.0. This value was obtained by impedimetric titration of the monolayer in the presence of Fe(CN)6 3-/4- as a redox probe. The extent of surface coverage was evaluated as 1.52 × 10-9 mol cm-2 based on charged consumed for reductive desorption of the monolayer in the 0.50 M NaOH solution. Then the sensor was used for determination of Ag(I) by square wave voltammetry. The parameters affecting the sensor response, such as pH and supporting electrolyte, were optimized. A dynamic calibration curve with two linear parts was obtained in the concentration ranges of 5 × 10-8-8 × 10-7 and 1 × 10-6-1 × 10-5 M of Ag(I). The detection limit adopted from cathodic striping square wave voltammetry was as 1 × 10-8 M for n = 7. Furthermore, the effect of potential interfering ions on the determination of Ag(I) was studied, and an appropriate method was used for the elimination of this effect. © 2005 Elsevier B.V. All rights reserved.
Analytical Chemistry (15206882) 78(14)pp. 4957-4963
Fabrication and electrochemical characterization of a novel nanosensor for determination of Cu2+ in subnanomolar concentrations is described. The sensor is based on gold cysteamine self-assembled monolayer functionalized with salicylaldehyde by means of Schiff's base formation. Cyclic voltammetry, Electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal microbalance were used to probe the fabrication and characterization of the modified electrode. The sensor was used for quantitative determination of Cu2+ by the EIS in the presence of parabenzoquinone in comparison with stripping Osteryoung square wave voltammetry (OSWV). The attractive ability of the sensor to efficiently preconcentrate trace amounts of Cu2+ allowed a simple and reproducible method for copper determination. A wide range linear calibration curve was observed, 5.0 × 10-10-5.0 × 10-6 and 5.0 × 10-10-5.0 × 10-6 M Cu2+, by using the EIS and OSWV, respectively. Moreover, the sensor presented excellent stability with lower than 10% change in the response, as tested for more than three months daily experiments, and a high repeatability with relative standard deviations of 6.1 and 4.6% obtained for a series of eight successive measurements in 5.0 × 10-7 M Cu2+ solution, by the EIS and OSWV, respectively. © 2006 American Chemical Society.
Sensors and Actuators B: Chemical (09254005) 115(2)pp. 614-621
A monolayers of cysteamine (CA) was prepared on a polycrystalline gold electrode through self-assembly procedure to produce a gold cysteamine self-assembled monolayers (Au-CA SAMs) modified electrode. Characterization of the modified electrode was performed by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was used to evaluate pKa of the adsorbed CA on the gold surface, and a value of 7.6 was obtained for the Au-CA surface pKa. The charged terminal groups of monolayers served for determination of dopamine (DA) in the presence of high concentration of ascorbic acid (AA) using differential pulse voltammetry (DPV). Well-separated DA and AA voltammetric waves (∼330 mV) were observed at the Au-CA SAMs electrodes in an acidic solution. A calibration curve with two linear parts was obtained for DA, 6.00 × 10-6 to 3.84 × 10-4 M and 3.36 × 10-4 to 9.50 × 10-3 M, with correlation coefficients 0.997 and 0.992, respectively. The detection limit for DA was found to be 2.31 μM in the presence of 1.0 mM AA. The apparent charge transfer rate constants (kapp) of AA and DA were evaluated by using EIS measurements on the modified electrode as 44.0 cm s-1 × 10-8 cm s-1 and 2.45 cm s-1 × 10-8 cm s-1, respectively. © 2005 Elsevier B.V. All rights reserved.
Analytica Chimica Acta (00032670) 562(2)pp. 223-228
A phosphate functionalized cysteamine self-assembled monolayer based on gold electrode is designed for uranyl ion (UO22+) detection. The response of the modified electrode is studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The EIS data are approximated using constant phase element (CPE) model from which kinetic and analytical parameters are evaluated. Uranyl ion is recognized based on blocking effect against charge transfer between p-benzoquinone as a probe and the modified electrode. This effect is detected from linear variation of charge transfer resistance (Rct) as a function of UO2 2+ concentration. From the analysis of the EIS data and approximated parameters, a method is developed for UO22+ determination based on impedimetric measurements. © 2006 Elsevier B.V. All rights reserved.
Journal of New Materials for Electrochemical Systems (14802422) 8(3)pp. 213-220
The aqueous suspended RuCl3 was coated into the pores of microporous Ni-Zn-P alloy and thermally decomposed at 400°C in an open furnace to produce composite electrodes (Ni-Zn-P-RuO2). The microporous alloy was prepared via a three-step layer-by-layer galvanostatic deposition. The electrocatalytic behavior of the electrode was investigated in the hydrogen evolution reaction (HER), by steady state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) in 1M NaOH solution at 25°C. The kinetics as Tafel slopes, double layer capacitances, and charge transfer resistances towards the HER were evaluated. The electrode is characterized by (i) a large real surface area of three orders of magnitude obtained from CV and EIS measurements, and (ii) high physical and electrochemical stability of RuO2 dispersed into the surface. The poisoning effect of cyanide ion on the HER was also studied by EIS. This study allowed us to select properly data for kinetics approximation. © J. New. Mat. Electrochem. Systems.
Surface and Coatings Technology (02578972) 198(1-3 SPEC. ISS.)pp. 123-128
Fabrication and electrochemical characterization of a self-assembled three layers modified gold electrode is described. The modification involves a three-step method; (i) preparation of cysteamine self-assembled monolayer, Au-CA, (ii) activation of Au-CA by glutaraldehyde to prepare Au-CA-GA, (iii) modification of Au-CA-GA by 2-Aminoethyl dihydrogen phosphate to functionalize the surface by phosphate groups, Au-CA-GA-AEDP. The resulting thin film modified electrode was tested successfully to recognize uranyl cations (UO22+) in aqueous solution. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to trace events in each step. The high affinity of the film towards the UO22+ was confirmed by EIS and CV results. The EIS data allowed recognition of UO22+ based on variation of the charge-transfer resistance (Rct) of the film as a function of the cation concentration. A dynamic range with more than three orders of magnitude was obtained. © 2004 Elsevier B.V. All rights reserved.
Journal of Applied Electrochemistry (15728838) 29(8)pp. 979-986
The surface roughness of porous Ni-Zn-P electrodes was studied in 1 M NaOH using in situ electrochemical techniques: ratio of the polarization current densities, electrochemical impedance spectroscopy, cyclic voltammetry, coulometric oxidation of the surface, and a new technique of a CO molecular probe. The obtained surface roughness was about 5.5×103. Good agreement was observed between the results obtained by all these techniques.
Journal of the Electrochemical Society (00134651) 145(7)pp. 2219-2225
Nickel-molybdenum-phosphorous electrodes were prepared by electrodeposition, and their activity for the hydrogen evolution reaction was studied in 1 M NaOH using electrochemical impedance spectroscopy and steady-state polarization techniques. Active and stable electrodes were obtained by deposition of three successive layers of Ni, Ni-P, and Ni-Mo-P and creating a concentration gradient in the topmost layer. It was found that the increase in electrode activity was due to increases in both the surface roughness and the intrinsic activity, as compared with Ni-P, Ni-Mo, and Ni electrodes. The reaction mechanism and the kinetic parameters were determined.
Journal of the Electrochemical Society (00134651) 144(8)pp. 2652-2657
Ni-Zn-P electrodes were prepared by subsequent deposition of Ni, Ni-P, and Ni-Zn-P layers. The topmost Ni-Zn-P layer was obtained by gradual addition of zinc to the plating bath. The obtained electrodes are more stable and more active toward the hydrogen evolution reaction than Ni-Zn alloys. They are characterized by low Tafel slopes and large surface roughness of 104. They may be attractive candidates for the alkaline water electrolysis.
Journal of the Electrochemical Society (00134651) 144(2)pp. 511-519
The hydrogen evolution reaction (HER) was studied on Ni-P electrodes containing 8 to 30 atomic percent P prepared by galvanostatic deposition. The electrodes were studied directly after preparation or after pretreatment by heating, leaching in HF solution, anodic oxidation, or potential cycling in the solution. The activity of these electrodes depended on the method of preparation and phosphorous content. The activity was higher for the materials deposited at lower temperatures and for those containing smaller amounts of phosphorous. The mechanism of the hydrogen evolution reaction was studied in 1 M NaOH, and the kinetic parameters were determined using steady-state polarization and electrochemical impedance spectroscopy techniques.
