Publication Date: 2021
RSC Advances (20462069)11(14)pp. 7862-7872
Curcumin is a polyphenolic compound with anti-oxidative and anti-cancer properties that is obtained from turmeric plants. Several studies have demonstrated that cancer cells are not killed unless they are exposed to 5-50 mM of curcumin. Consequently, it is vital to control the concentration of curcumin in cancer therapy. In this study, a sensitive electrochemical sensor was fabricated based on a beta-cyclodextrin-reduced graphene oxide (β-CD-rGO) nanocomposite for measuring curcumin concentration. The effects of experimental factors were investigated and the optimum parametric conditions were determined using the Taguchi optimization method. The β-CD-rGO modified electrode exhibited good electrochemical properties for curcumin detection. The results of differential pulse voltammetry experiments unveiled that the sensor shows a linear response to curcumin concentration over the range of 0.05-10 mM with a detection limit of 33 nM and sensitivity of 4.813 μA μM−1. The fabricated sensor exhibited selectivity in the presence of other electroactive species,e.g., propranolol, clomipramine and clonazepam. © The Royal Society of Chemistry 2021.
Publication Date: 2021
Advanced Materials Technologies (2365709X)6(10)
Nanochannels offer significant practical advantages in many fields due to their interesting characteristics, such as flexibility in shape and size, robustness, low-cost and their ability to be modified based on the required applications. The effectiveness of ion separation in nanochannels can be assessed based on the selective transport of the desired ions and the rate of the transportation process. This paper aims to provide an extensive review of ion-based nanochannels, including their working principles and ion-selective behaviors. Nanochannel fabrication strategies and their applications are discussed. Key nanochannel design factors and their roles in governing ion-selective transport are also reviewed. The contribution of size, charge, wettability, and recognition ability of the nanochannels on the selectivity mechanisms are discussed. Specific consideration is made to nanochannel applications in sensing and biosensing assays. Finally, an attempt is made to address the commercial implementation and future outlook of the nanochannels to guide researchers in emerging avenues of research. © 2021 Wiley-VCH GmbH
Publication Date: 2021
Journal of Membrane Science (0376-7388)639
2-D materials with nanofluidic channels have gained significant attention for their potential as an ion separation membrane. However, the fundamental understanding of the interactions between nanochannel sizes and ion selectivity and conductivity remains complex as experimentally controlling the free interlayer spacing in sub-nanometer scales is challenging. Herein, we utilize molecular dynamic (MD) simulations to tailor the free interlayer spacing between a model 2-D MXene membrane to understand their effects on ion transport behaviour. As a validation, the free interlayer spacing of the MXene nanosheets was altered by impregnating different type of ions, which is then used in an electrically driven ion separation system. The simulation result shows that as the free interlayer spacing increases from below to above 6 Å, the selectivity of monovalent Li+ and K+ compared to Mg2+ decreases due to the reduced entrance energy barrier for Mg2+; however, higher overall ionic conductivity can be achieved. The experimental data using a membrane with free interlayer spacing between 6 and 7 Å agrees well with the simulation study. The difference in the ion permeation of H+, K+, Na+, Li+, Ca2+, and Mg2+ was not only attributed to the nanochannel size but also considering the degree of ion dehydration and ions interactions to the –O binding site of the membrane. Further investigations demonstrated that ion transport mechanism through MXene nanochannels followed the surface-charge-governed behaviour in HCl and KCl solutions at different concentrations, as evident from significantly higher ionic and proton conductivity at low concentrations (<10−3 M) compared to the bulk solutions. This work leads to a better understanding of 2-D nanochannel design in ion transport applications. © 2021 Elsevier B.V.
Publication Date: 2020
Sensors and Actuators, B: Chemical (09254005)304
Considering the importance of measuring insulin in the prevention and diagnosis of diabetes-related illnesses, here we introduced an ultrasensitive electrochemical aptamer-based sensor for detection of insulin in human blood serum. In this research, carbon quantum dots (CQDs) were synthesized using simple, fast and cheap methods from candle soot. By dispersion of the CQDs in chitosan (Chi) matrix, homogenous CQD-Chit nano-composite was obtained. The experimental results demonstrate the good advantages of proposed CQD-Chit nano-composite, such as homogeneity, high stability and multiple amino groups for covalent immobilization of aptamer and fabrication of highly selective insulin aptasensor. CQD-Chit nano-composite was characterized by the transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDAX), Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques. Under the optimized conditions with electrochemical impedance spectroscopy technique, a linear response ranges from 0.5 nM to 10 nM with the sensitivity of 80.07 Ω/nM and the very low detection limit of 106.8 pM was obtained for insulin detection. The fabricated aptasensor is validated in comparison with standard methods for detection of insulin in human blood serum. Also, the analytical performances of the fabricated aptasensor can be a superiority compared to the current insulin electrochemical biosensors. © 2019
Publication Date: 2019
Journal of Biotechnology (01681656)306pp. 1-8
Carcinoembryonic antigen (CEA), a highly glycosylated protein, overexpresses in many cancers. In this study, computational methods were used to optimize CEA aptamers. Experimental evaluvation of selected aptamers were conducted through electrochemical impedance spectroscopy. After two and three-dimensional structure modeling, the complexes of twelve reported aptamers against CEA were simulated using the ZDOCK server. Based on docking scores, two aptamer sequences (CSR59 and CSR57.1) were selected and used to create a new library. This ssDNA aptamer library consisting of 91 sequences was created using diverse in silico mutational methods. We obtained seventeen sequences having higher binding scores than reported sequences. Based on ZDOCK scores, the interaction domain of CEA, and steric hindrance due to glycosylation, two aptamer sequences (G3S1.5 and G2S2.2) were selected. An impedimetric aptasensor was designed, and selected aptamers were used as biorecognition elements. Resistance to charge transfer (Rct) quantities confirmed the bioinformatic approach and molecular docking scores. The result showed that the interaction ability of selected aptamers was about 13.5 fold higher than the control. It can be concluded that the selected aptamers have good potential for detection of carcinoembryonic antigen biomarker. © 2019
Publication Date: 2019
Journal Of Applied Electrochemistry (0021891X)49(1)pp. 87-97
Abstract: Aptamers are affinity molecules with high specificity, proposed as excellent alternatives to antibodies in targeting and detecting applications due to their smaller size, higher stability, and simplicity of production and modification compared with antibodies. Due to lack of a sensitive and simple method to quantitatively evaluate attachment of aptamer to nanoparticles (NPs), optimization of the attachment process was not considered in most of previously studied aptamer-targeted drug delivery systems. The aim of current study was to demonstrate the utility of electrochemical impedance spectroscopy (EIS) technique in this field. Ecoflex® polymeric NPs loaded with docetaxel (DTX-NPs) were fabricated via electrospraying technique, and HER-2-specific aptamer molecules were attached via amide bonds (Apt-DTX-NPs). Using EIS method, the time period of various stages of aptamer conjugation was optimized, by comparing the amount of aptamer molecules attached to the DTX-NPs. The results of in vitro studies on optimum Apt-DTX-NPs demonstrated that the proposed delivery system could significantly enhance the cellular uptake and the cytotoxic effect against HER-2 positive cell line in comparison with non-targeted or Herceptin-targeted DTX-NPs. Thus, aptamer conjugation could improve the in vitro performance of Ecoflex NPs, which could be suggested as a potential DTX delivery system in HER-2 overexpressing cancers. In this regard, EIS method could play its role as a sensitive quantification method to obtain the optimized aptamer-conjugated NP systems. Graphical abstract: [Figure not available: see fulltext.]. © 2018, Springer Nature B.V.
Publication Date: 2019
Water Research (0043-1354)159pp. 313-323
In the last two years, the rapidly rising demand for lithium has exceeded supply, resulting in a sharp increase in the price of the metal. Conventional electric driven membrane processes can separate Li+ from divalent cations, but there is virtually no commercial membrane that can efficiently and selectively extract Li+ from a solution containing chemically similar ions such as Na+ and K+. Here, we show that the different movement behavior of Li+ ion within the sub-nanometre channel leads to Li+ ion-selectivity and high transport rate. Using inexpensive negatively charged 2D subnanometer hydrous phyllosilicate channels with interlayer space of 0.43 nm in a membrane-like morphology, we observed that for an interlayer spacing of below 1 nm, Li+ ions move along the length of the channel by jumping between its two walls. However, for above 1 nm spacing, the ions used only one channel wall to jump and travel. Molecular dynamic (MD) simulation also revealed that ions within the nanochannel exhibit acceleration-deceleration behavior. Experimental results showed that the nanochannels could selectively transport monovalent ions of Li+> Na+> and K+ while excluding other ions such as Cl− and Ca2+, with the selectivity ratios of 1.26, 1.59 and 1.36 for Li+/Na+, Li+/K+, and Na+/K+ respectively, which far exceed the mobility ratios in traditional porous ion exchange membranes. The findings of this work provide researchers with not only a new understanding of ions movement behavior within subnanometer confined areas but also make a platform for the future design of ion-selective membranes. © 2019 Elsevier Ltd
Publication Date: 2019
Biosensors and Bioelectronics (09565663)131pp. 1-8
In the present work, for the first time we takes the advantages of chitosan-Nafion (Chit-Naf) composite as a highly conductive surface platform and a novel CNT-based signal amplification strategy to develop a lable-free impedimetricaptamer-based sensor for highly sensitive detection of As(III). The electrochemical impedance spectroscopy (EIS) investigations surprisingly revealed that the glassy carbon electrode (GC) electrode modified with Chit-Naf composite had higher electron transfer kinetics compared the bare GC, GC/Naf and GC/Chit electrodes, which promises a great potential as an efficient platform in construction of biosensing assays. In this work, we employed a signal amplification strategy based on carbon nanotube-bovine serum albumin (CNT-BSA) hybrid system, by which sensitivity and detection limit of the aptasensor for the detection of As(III) were obtained to be 100.82 Ω nM −1 and a of 74 pM, respectively. This protocol provided one of the lowest limits of detection for As(III) on aptamer-based electrodes recently described in the literature. Moreover, the change of the optical absorptive properties of CNTs upon biorecognition interactions provides a way to detect the biorecognition process and thus allowed us to design an optical As(III) aptasensor using the UV–Vis spectroscopic method. The discrimination capability of the fabricated aptasensor for recognizing As(III) in the presence of other metal ions and a complex matrix of waste water samples was successfully investigated. This protocol provided a new method for sensitive detection of As(III) with considerable advantages in terms of reproducibility, selectivity, being mediator free and regenerability of the sensing interface. © 2019 Elsevier B.V.
Publication Date: 2019
IET Nanobiotechnology (17518741)13(8)pp. 829-833
Human epidermal growth factor receptor 2 (HER-2) is overexpressed in 20-30% of human breast cancers, associated with poor prognosis and tumour aggression. The aim of this study was the production of trastuzumab-targeted Ecoflex nanoparticles (NPs) loaded with docetaxel and in vitro evaluation of their cytotoxicity and cellular uptake. The NPs were manufactured by electrospraying and characterised regarding size, zeta potential, drug loading, and release behaviour. Then their cytotoxicity was evaluated by MTT assay against an HER-2-positive cell line, BT-474, and an HER-2-negative cell line, MDA-MB-468. The cellular uptake was studied by flow cytometry and fluorescent microscope. The particle size of NPs was in an appropriate range, with relatively high drug entrapment and acceptable release efficiency. The results showed no cytotoxicity for the polymer, but the significant increment of cytotoxicity was observed by treatment with docetaxel-loaded NPs in both HER-2-positive and HER-2-negative cell lines, in comparison with the free drug. The trastuzumab-targeted NPs also significantly enhanced cytotoxicity against BT-474 cells, compared with non-targeted NPs. © The Institution of Engineering and Technology 2019
Publication Date: 2018
Journal of Immunological Methods (00221759)458pp. 26-32
Hepatitis B virus (HBV) infection is the major public health problem leading cause of death worldwide. The most important diagnostic marker for this infection is hepatitis B surface antigen (HBsAg). In this study, a novel, inexpensive, portable and sensitive ELISA method was designed and investigated for diagnosis of HBsAg based on the functionalized Fe3O4 and Al2O3 nanoparticles, with the strategy for detecting the concentration of glucose using a cheap and accessible personal glucose meter (PGM). The ELISA system was constructed using hepatitis B antibody against HBsAg immobilized on streptavidin coated magnetic iron oxide particles (S-Fe3O4) as the capture antibody (Ab1). In addition, another hepatitis B antibody against different epitope of HBsAg (Ab2) and glucoamylase both were immobilized on Al2O3 nanoparticles. After formation of the sandwich immune complex between Ab1 and Ab2 immobilized on S-Fe3O4 and Al2O3 NPs, respectively, through HBsAg, starch was converted into glucose using glucoamylase. Then, the glucose concentration was measured using PGM. The concentration of HBsAg was calculated based on the linear relation between the concentrations of HBsAg and glucose. Under optimal conditions, this assay showed detection limit values of 0.3 to 0.4 ng ml−1 for “ay” and “ad” subtypes of HBsAg, respectively. The results indicate that the designed assay is comparable to the commercial kits in terms of sensitivity, on-site, specificity, cost, simplicity, portability and reproducibility. The presented method can be used in disadvantaged areas of the world and blood transfusion centers. To the best of our knowledge, this is the first report of using PGMs for HBSAg detection. © 2018 Elsevier B.V.
Publication Date: 2018
Colloids and Surfaces B: Biointerfaces (09277765)165pp. 135-143
Nickel-cysteine nanostructures (Ni-CysNSs) are prepared by a simple wet chemistry procedure under mild conditions, in which L-cysteine acts both as precursor and structure directing agent. This method involves the reaction of nickel chloride with L-cysteine, followed by simultaneous adjusting the pH in the range of 6–8.5 by addition of an aqueous NaOH solution. The structure and morphology of the prepared products are characterized using various techniques, including X-ray powder diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, CHNS elemental analysis, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). The effects of a variety of synthetic conditions on the structure and morphology of the Ni-CysNSs are studied, including the molar ratio of precursors, dispersing solvent, pH value of the reaction solution, reaction time and reaction temperature. FT-IR measurements reveal that synthesized Ni-CysNSs contain many free carboxylic groups on the surface, which could be used as binding sites to anchor biological molecules in order to develop various bioelectronic devices. In this work, the applicability of synthesized nanostructure in biosensing is studied by using Ni-CysNSs as a platform for covalently immobilization of GOx, as a model enzyme, on the surface. Cyclic voltammetric measurements reveal that the direct electron transfer from the active center of GOx to the glassy carbon electrode facilitated upon its immobilization on the Ni-CysNSs film. More importantly, GOx preserves its native structure and catalytic activity for the oxidation of glucose after immobilization on the Ni-CysNSs surface. The electrocatalytic characteristics of the GC/NiCysNS/GOx electrode toward the oxidation of glucose are investigated by cyclic voltammetry, which displayed acceptable electrical and sensing performance. Simple preparation of Ni-CysNPs and their biocompatibility make them attractive platforms for integration of various biomolecules such as proteine/enzymes with surface. © 2018
Publication Date: 2018
Drug Development and Industrial Pharmacy (03639045)44(6)pp. 1012-1022
Objective: Ovarian cancer is still a major cause of morbidity and mortality. Docetaxel (DTX) is one of the most notable cytotoxic agents for treatment of ovarian cancer. However, its side effects proposed considerable problems to the patients. Significance: Polymeric nanoparticles (NPs) of poly (butylene adipate-co-butylene terephthalate) (Ecoflex®), a biodegradable and biocompatible polymer, were prepared for the first time by the upgradeable electrospraying technique. Methods: The formulation and procedure variables were optimized using Design Expert software, and effect of each variable on particle size, particle size distribution, drug entrapment efficiency, and drug release of the NPs were evaluated. Then, in vitro cytotoxicity, cellular uptake, X-ray diffraction pattern, and morphological characteristics of the optimized NPs were evaluated. Finally, in vivo efficacy of the DTX-loaded NPs was evaluated on tumor bearing nude mice. Results: The optimum condition for production of NPs included voltage of 20 kV, 12 cm distance between electrodes, feeding rate of 1 mL/hr, polymer to drug ratio of 3:1, 1 w/v% of Pluronic-F127 and dichloromethane to dimethyl formamide ratio of 2.7:1. Fluorescent microscopy test showed the NPs were successfully up-taken by ovarian cancer cells. In vitro cytotoxicity test confirmed no cytotoxic effect caused by blank NPs, while cell viability of the DTX loaded NPs was significantly lower than the free DTX (p <.05). The NPs significantly enhanced anti-tumor efficacy of the drug in nude mice (p <.05). Conclusion: The Ecoflex® NPs could potentially provide a suitable alternative for currently available formulations of DTX. © 2018 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2017
Electroanalysis (15214109)29(7)pp. 1838-1838
The surname of the third author is misspelled. It should read Mohammad Rafienia. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2017
Electroanalysis (15214109)29(4)pp. 1113-1123
The present study describes a novel and very sensitive electrochemical assay for determination of hydrogen peroxide (H2O2) based on synergistic effects of reduced graphene oxide- magnetic iron oxide nanocomposite (rGO-Fe3O4) and celestine blue (CB) for electrochemical reduction of H2O2. rGO-Fe3O4 nanocomposite was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy and cyclic voltammetry. Chitosan (Chit) was used for immobilization of amino-terminated single-stranded DNA (ss-DNA) molecules via a glutaraldehyde (GA) to the surface of rGO-Fe3O4. The MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) results confirmed the biocompatibility of nanocomposite. Experimental parameters affecting the ss-DNA molecules immobilization were optimized. Finally, by accumulation of the CB on the surface of the rGO-Fe3O4-Chit/ssDNA, very sensitive amperometric H2O2 sensor was fabricated. The electrocatalytic activity of the rGO-Fe3O4-Chit/DNA-CB electrode toward H2O2 reduction was found to be very efficient, yielding very low detection limit (DL) of 42 nM and a sensitivity of 8.51 μA/μM. Result shows that complex matrices of the human serum samples did not interfere with the fabricated sensor. The developed sensor provided significant advantages in terms of low detection limit, high stability and good reproducibility for detection of H2O2 in comparison with recently reported electrochemical H2O2 sensors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2017
Biosensors and Bioelectronics (09565663)95pp. 117-123
The present work describes an ultrasensitive electrochemical aptamer-based assay for detection of human epidermal growth factor receptor 2 protein (HER2) cancer biomarker as a model analyte. Results show that the reduced graphene oxide-chitosan (rGO-Chit) film as a suitable electrode material possesses great favorable properties including high homogeneity, good stability, large surface area and high fraction of amine groups as aptamer binding sites. Various steps of aptasensor fabrication were characterized using microscopic, energy-dispersive X-ray spectroscopy (EDAX), Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques. Using methylene blue (MB) as an electrochemical probe and differential pulse voltammetry (DPV) technique, two linear concentration ranges of 0.5–2 ng ml−1 and 2–75 ng ml−1 were obtained with a high sensitivity of 0.14 μA ng−1 ml and a very low detection limit of 0.21 ng ml−1 (very lower than the clinical cut-off). The fabricated aptasensor showed excellent selectivity for detection of HER2 in complex matrix of human serum samples. The sensitive detection of HER2 can be attributed to the multiple signal amplification of MB during its accumulation to the modified electrode surface via both affinity interaction to aptamer molecules and electrostatic adsorption to the HER2 analyte as well as high charge transfer kinetic properties of the applied rGO-Chit film. The rapid and simple preparation of the proposed aptasensor as well as its high selectivity, stability and reproducibility provided a promising protocol for non-invasive diagnosis for various points of care application. The proposed aptasensor showed excellent analytical performance in comparison with current HER2 biosensors. © 2017
Publication Date: 2016
Microchemical Journal (0026265X)129pp. 310-317
In the present work, for the first time, excellent activity and antifouling properties of reduced graphene oxide (rGO) nanosheets toward the oxidation of insulin at physiological pH were reported. Electrochemical oxidation of insulin at the surface of rGO, graphene oxide (GO) and graphite (G) were investigated and compared. Cyclic voltammetry and hydrodynamic amperometry were used to investigate the analytical characteristics of the rGO-modified GC (GC/rGO) electrode toward the oxidation of insulin. While the electrooxidation of insulin on the bare glassy carbon (GC) electrode, G and GO-modified GC electrodes led to the deactivation of the surface after a short period of time, the GC electrode coated with rGO revealed highly stable insulin oxidation current. The effect of various experimental parameters on the electrochemical oxidation of insulin was investigated using cyclic voltammetric technique. The amperometric response of the GC/rGO electrode toward insulin under the optimum conditions was found to be linear over the concentration range of 4–640 nM with a sensitivity of 7.1254 nA/nM and a detection limit of 350 pM. The modified electrode offers considerable advantages of simple and fast electrode preparation, low cost, fast response time, signal stability, high sensitivity and insulin determination at physiological pH. © 2016
Publication Date: 2016
Electroanalysis (10400397)28(5)pp. 1134-1145
The performance of carboxylic acid functionalized carbon nanotubes (CNTs(COOH)), chitosan (Chit), carbon nanotubes-chitosan (CNTs-Chit and CNTs(COOH)-Chit) for immobilizing of amino-functionalized ssDNA and fabrication of electrochemical prostate specific antigen (PSA) aptasensor were studied in detail using X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy (EIS). The assemblies of capture probe are formed on the surface via two approaches: EDC/NHS chemistry and glutaraldehyde linker. Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and EIS techniques were used to investigate the analytical performance of the PSA aptasensor. Under optimum conditions the sensitivity of 0.0026μA/(ng/ml) and a limit of detection of 0.75ng/ml (22 pM) were obtained for PSA detection. This protocol offers a new means for sensitive detection of PSA with some advantages in terms of simplicity, selectivity, ease of use and regenerability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2014
Electroanalysis (10400397)26(12)pp. 2716-2726
Cobalt oxide nanostructure (CoOxNS) deposited on the glassy carbon (GC) electrode surface is proposed as a novel electrocatalytic system for the reduction of para-Nitrophenol. Cyclic voltammetry, electrochemical impedance spectroscopy, atomic force microscopy and scanning electron microscopy were used for characterization of deposited CoOxNS. CoOxNS deposited by cycling at positive potentials (0 to +1.3V) show less charge-transfer resistance (Rct) and more catalytic activity for the electroreduction of p-nitrophenol compared to those CoOxNS obtained by scanning the applied potential throughout a negative V range. The GC/CoOxNS electrode showed good electrocatalytic activity toward the reduction of p-nitrophenol at different pH values. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2014
Biosensors and Bioelectronics (18734235)56pp. 313-319
Herein we describe improved electron transfer properties and catalytic activity of nickel oxide nanoparticles (NiONPs) via the electrochemical deposition on DNA modified glassy carbon electrode (DNA/GCE) surface. NiONPs deposited on the bare and DNA-coated GCE showed different morphologies, electrochemical kinetics and catalytic activities. The atomic force microscopy (AFM) images revealed the formation of triangular NPs on the DNA/GCE that followed the shape produced by the DNA template, while the electrodeposition of NiONPs on the bare GCE surface led to the formation of spherical nanoparticles. Electrochemical impedance spectroscopy (EIS) measurements revealed lower charge-transfer resistance (Rct) of triangular NiONPs compared to spherical NPs. Furthermore, the electrocatalytic activity of triangular NiONPs compared to spherical NPs toward glucose oxidation in alkaline media was significantly improved. The amperometric oxidation of glucose at NiONP-DNA/GCE, yielded a very high sensitivity of 17.32mAmM-1cm-2 and an unprecedented detection limit of 17nM. The enhanced electron transfer properties and electrocatalytic activity of NiONP-DNA/GCE can be attributed to the higher fraction of sharp corners and edges present in the triangular NiONPs compared to the spherical NPs. The developed sensor was successfully applied to the determination of glucose in serum samples. © 2014 Elsevier B.V.
Publication Date: 2013
Sensors and Actuators, B: Chemical (09254005)176pp. 335-343
A novel, highly sensitive sensor for detection of persulfate (S 2O82-) is demonstrated by modification of carbon paste electrode (CPE) with nickel oxide nanowires (NiOx NWs) and neutral red (NR). Ni NWs are prepared by DC electrodeposition of Ni in the cylindrical pores of anodized aluminum oxide (AAO) templates. NWs are released, oxidized and immobilized with NR on the surface of CPE. Cyclic voltammetry studies demonstrate a pair of well-defined nearly reversible redox couples (E°′ = -0.2 V in a buffer solution pH 2.0) at a wide pH range of 1-12. The surface coverage and heterogeneous electron transfer rate constant of the adsorbed redox couple are 7.368 × 10-12 mol cm-2 and 7.9 s-1, respectively, indicating a high NR loading efficiency for NiOx NWs and efficient electron transfer between redox couple and the electrode. The modified CPE exhibits an excellent electrocatalytic activity for a S 2O82- reduction, with a measured k cat of ∼7.14 × 103 M-1 s -1. This catalytic reduction allows an amperometric detection of S2O82- at a potential of -0.2 V with detection limit of 30 nM, concentration calibration range of 0.1 μM to 12 mM and a linear sensitivity of 647.33 nA μM-1, respectively. © 2012 Elsevier B.V. All rights reserved.
Publication Date: 2011
Electrochimica Acta (00134686)56(9)pp. 3387-3394
A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20-100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1-12). The surface coverages and heterogeneous electron transfer rate constants (ks) of immobilized Mn-complex were approximately 1.58 × 10-10 mole cm-2 and 48.84 s-1. The modified electrode showed excellent electrocatalytic activity toward H2O2 reduction. Detection limit, sensitivity, linear concentration range and kcat for H 2O2 were, 0.2 μM and 692 nA μM-1 cm -2, 1 μM to 1.5 mM and 7.96(±0.2) × 103 M-1 s-1, respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability. © 2010 Elsevier Ltd. All rights reserved.
Publication Date: 2011
Biosensors and Bioelectronics (18734235)30(1)pp. 188-196
A sensitive electrochemical method for DNA hybridization based on immobilization of DNA probe and [Ru(NH 3) 5Cl]PF 6 complex onto nickel oxide nanomaterials (NiOx np) modified glassy carbon electrode was developed. Due to strong affinity of NiOx np for phosphate groups, oligonucleotides probe with a terminal 5'-phosphate group was attached to the surface of the modified electrode. DNA immobilization and hybridization were characterized by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry using K 3Fe(CN) 6/K 4Fe(CN) 6 and [Ru(NH 3) 5Cl]PF 6 as probe and indicator, respectively. The Ru-complex current response indicates only the complementary sequence showing an obvious current signal in comparison to non-complementary and three or single point mismatched sequences. The fabricated biosensor possessed good selectivity and sensitivity for complementary probe, taxon: 32630 tumor necrosis factor (TNF). The linear dynamic range, sensitivity and detection limit of the proposed biosensor were 4×10 -10M to 1×10 -8M, 34.32nAnM -1 and 6.8×10 -11M, respectively. Excellent reproducibility and stability, quite simple and inexpensive preparation are the other advantages of proposed biosensor. © 2011 Elsevier B.V.
Publication Date: 2011
Electroanalysis (10400397)23(3)pp. 683-691
Direct electron transfer of immobilized copper, zinc-superoxide dismutase (SOD) onto electrodeposited nickel-oxide (NiOx) nanoparticle modified glassy carbon (GC) electrode displays a well defined redox process with formal potential of -0.03V in pH7.4. Cyclic voltammetry was used for deposition of (NiOx) nanoparticles and immobilization of SOD onto GC electrode. The surface coverage (Γ) and heterogeneous electron transfer rate constant (ks) of immobilized SOD are 1.75×10-11molcm-2 and 7.5±0.5s-1, respectively. The biosensor shows a fast amperometric response (3s) toward superoxide at a wide concentration range from 10μM to 0.25mM with sensitivity of 13.40nAμM-1cm-2 and 12.40nAμM-1 cm-2, detection limit of 2.66 and 3.1μM based on anodically and cathodically detection. This biosensor exhibits excellent stability, reproducibility and long life time. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2011
Journal of Solid State Electrochemistry (14328488)15(9)pp. 2041-2052
A simple method was used to fabricate flavin adenine dinucleotide (FAD)/NiOx nanocomposite on the surface of glassy carbon (GC) electrode. Cyclic voltammetry technique was applied for deposition nickel oxide nanostructures onto GC surface. Owing to its high biocompatibility and large surface area of nickel oxide nanomaterials with immersing the GC/NiOx-modified electrode into FAD solution for a short period of time, 10-140 s, a stable thin layer of the FAD molecules immobilized onto electrode surface. The FAD/NiOx films exhibited a pair of well-defined, stable, and nearly reversible CV peaks at wide pH range (2-10). The formal potential of adsorbed FAD onto nickel oxide nanoparticles film, E o′ vs. Ag/AgCl reference electrode is -0.44 V in pH 7 buffer solutions was similar to dissolved FAD and changed linearly with a slope of 58.6 mV/pH in the pH range 2-10. The surface coverage and heterogeneous electron transfer rate constant (k s) of FAD immobilized on NiOx film glassy carbon electrode are 4.66×10 -11 mol cm -2 and 63± 0.1 s -1, indicating the high loading ability of the nickel oxide nanoparticles and great facilitation of the electron transfer between FAD and nickel oxide nanoparticles. FAD/NiOx nanocomposite-modified GC electrode shows excellent electrocatalytic activity toward S 2O 8 2- reduction at reduced overpotential. Furthermore, rotated modified electrode illustrates good analytical performance for amperometric detection of S 2O 8 2-. Under optimized condition, the concentration calibration range, detection limit, and sensitivity were 3 μM- 1.5 mM, 0.38 μM and 16.6 nA/μM, respectively. © Springer-Verlag 2010.
Publication Date: 2011
Electrochimica Acta (00134686)56(17)pp. 6097-6105
For the first time a novel, simple and facile approach is described to construct highly stable glucose oxidase (GOx) multilayer onto glassy carbon (GC) electrode using thiourea (TU) as a covalent attachment cross-linker. The layer by layer (LBL) attachment process was confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and Fourier transform infrared reflection spectroscopy (FT-IR-RS) techniques. Immobilized GOx shows excellent electrocatalytic activity toward glucose oxidation using ferrocenemethanol as artificial electron transfer mediator and biosensor response was directly correlated to the number of bilayers. The surface coverage of active GOx per bilayer, heterogeneous electron transfer rate constant (ks) and Michaelis-Menten constant (KM), of immobilized GOx were 1.50 × 10-12 mol cm-2, 9.2 ± 0.5 s-1 and 3.42(±0.2) mM, respectively. The biosensor constructed with four-bilayers of TU/GOx showed good stability, high reproducibility, long life-time, fast amperometric response (5 s) with the high sensitivity of 5.73 μA mM -1 cm-2 and low detection limit of 6 μM at concentration range up to 5.5 mM. © 2011 Elsevier Ltd. All Rights Reserved.
Publication Date: 2010
Electroanalysis (10400397)22(14)pp. 1599-1606
Direct electron transfer of immobilized superoxide dismutase (Cu, Zn-SOD) onto silicon carbide (SiC) nanoparticles displays a pair of well defined and nearly reversible redox peaks with formal potential (E°') of -0.03 V in pH 7.4. The heterogeneous electron transfer rate constant (ks) and surface coverage (Γ) of immobilized SOD are 11.0±0.4 s-1 and 1.42x10-11 mol cm-2. Biosensor shows fast amperometric response (3s) with sensitivity and detection limit of 1.416 nA μM-1, 1.66 μM, and 1.375 nA μM-1, 2.1 μM for cathodically or anodically detection of superoxide, respectively. This biosensor also exhibits good stability, reproducibility and long life-time. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.
Publication Date: 2009
Electrochimica Acta (00134686)54(26)pp. 6312-6321
A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5-120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2-12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (ks) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10-10 mol cm-2, 6.12 s-1, 5.9 × 10-10 mol cm-2 and 6.58 s-1, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 103 M-1 s-1 and 5.5 (±0.2) × 103 M-1 s-1, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM-1 nA μM-1 and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM-1, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction. © 2009 Elsevier Ltd. All rights reserved.
Publication Date: 2008
Electroanalysis (10400397)20(16)pp. 1788-1797
A simple procedure was developed to prepare a glassy carbon electrode modified with multi walled carbon nanotubes (MWCNTs) and Celestin blue. Cyclic voltammograms of the modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range (2-12). The formal potential of redox couple (E′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of Celestine blue immobilized on CNTs glassy carbon electrode was approximately 1.95 × 10-10 mol cm-2. The charge transfer coefficient (α) and heterogeneous electron transfer rate constants (ks) for GC/MWCNTs/Celestine blue were 0.43 and 1.26 s-1, respectively. The modified electrode show strong catalytic effect for reduction of hydrogen peroxide and oxygen at reduced overpotential. The glucose biosensor was fabricated by covering a thin film of sol-gel composite containing glucose oxides (GOx) on the surface of Celestine blue /MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 0.3 μM, 18.3 mA/μM and 10 μM-6.0 mM, respectively. The accuracy of the biosensor for glucose detection was evaluated by detection of glucose in a serum sample, using standard addition protocol. In addition biosensor can reach 90% of steady currents in about 3.0 sec and interference effect of the electroactive existing species (ascorbic acid-uric acid and acetaminophen) was eliminated. Furthermore, the apparent Michaelis-Menten constant 2.4 mM, of GOx on the nano composite exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of glucose biosensor. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
Publication Date: 2007
Sensors and Actuators, B: Chemical (09254005)123(1)pp. 530-537
The electrocatalytic reduction of nitrite, iodate and periodate has been studied at catalase-incorporated multi-wall carbon nanotubes (MWCNTs) supported on a glassy carbon electrode. Cyclic voltammograms of the catalase-incorporated MWCNTs indicate a pair of well defined and nearly reversible redox couple. The embedded catalase in the MWCNTs films show excellent electrocatalytic activity toward iodate, nitrite and periodate reduction in acidic solutions at unusually positive potentials. Furthermore, catalase-modified MWCNTs supported on a glassy carbon rotating disk electrode shows good analytical performance for amperometric determination of selected anions. Under optimized condition of the amperometry method the concentration calibration range, detection limit and sensitivity are 1 μM to 6 mM, 0.15 μM and 55.6 nA/μM for periodate, 1 μM to 5 mM, 0.2 μM and 44.4 nA/μM for iodate and 5 μM to 10 mM, 1.35 μM and 7 nA/μM for nitrite, respectively. Meanwhile, the catalase activity in the carbon nanotubes films is significantly enhanced with apparent Michaelis-Menten constants of 0.9, 1.41 and 1.14 mM for iodate, periodate and nitrite, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long term life, fast amerometric response (within 5 s), wide linear range, technical simplicity and possibility of preparation at a short period of time are great advantages of this sensor. The obtained results show potential and promising practical application for the catalase-MWCNTs-modified electrode in amperometric sensor for oxoanions determination. This sensor can be used as an amperometric detector for analysis of nitrite, iodate and periodate in chromatographic or flow systems. © 2006 Elsevier B.V. All rights reserved.
Publication Date: 2007
Biophysical Chemistry (03014622)125(2-3)pp. 540-548
Cyclic voltammetry was used for simultaneous formation and immobilization of nickel oxide nano-scale islands and catalase on glassy carbon electrode. Electrodeposited nickel oxide may be a promising material for enzyme immobilization owing to its high biocompatibility and large surface. The catalase films assembled on nickel oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at about - 0.05 V vs. SCE at pH 7, characteristic of the heme Fe (III)/Fe (II) redox couple. The formal potential of catalase in nickel oxide film were linearly varied in the range 1-12 with slope of 58.426 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The electron transfer between catalase and electrode surface, (ks) of 3.7(± 0.1) s- 1 was greatly facilitated in the microenvironment of nickel oxide film. The electrocatalytic reduction of hydrogen peroxide at glassy carbon electrode modified with nickel oxide nano-scale islands and catalase enzyme has been studied. The embedded catalase in NiO nanoparticles showed excellent electrocatalytic activity toward hydrogen peroxide reduction. Also the modified rotating disk electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant catalase/nickel oxide modified glassy carbon electrodes exhibited fast amperometric response (within 2 s) to hydrogen peroxide reduction (with a linear range from 1 μM to 1 mM), excellent stability, long term life and good reproducibility. The apparent Michaelis-Menten constant is calculated to be 0.96(± 0.05)mM, which shows a large catalytic activity of catalase in the nickel oxide film toward hydrogen peroxide. The excellent electrochemical reversibility of redox couple, high stability, technical simplicity, lake of need for mediators and short preparations times are advantages of this electrode. Finally the activity of biosensor for nitrite reduction was also investigated. © 2006 Elsevier B.V. All rights reserved.
Publication Date: 2007
Electroanalysis (10400397)19(10)pp. 1100-1108
A new H2O2 enzymeless sensor has been fabricated by incorporation of thionin onto multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode. First 50 μL of acetone solution containing dispersed MWCNTs was pipetted onto the surface of GC electrode, then, after solvent evaporations, the MWCNTs modified GC electrode was immersed into an aqueous solution of thionin (electroless deposition) for a short period of time < 5-50 s. The adsorbed thin film of thionin was found to facilitate the reduction of hydrogen peroxide in the absence of peroxidase enzyme. Also the modified electrode shows excellent catalytic activity for oxygen reduction at reduced overpotential. The rotating modified electrode shows excellent analytical performance for amperometric determination of hydrogen peroxide, at reduced overpotentials. Typical calibration at -0.3 V vs. reference electrode, Ag/AgCl/3 M KCl, shows a detection limit of 0.38 μM, a sensitivity of 11.5 nA/μM and a liner range from 20 μM to 3.0 mM of hydrogen peroxide. The glucose biosensor was fabricated by covering a thin film of sol-gel composite containing glucose oxides on the surface of thionin/MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 1 μM, 18.3 μA/mM and 10 μM-6.0 mM, respectively. In addition biosensor can reach 90% of steady currents in about 3.0 s and interference effect of the electroactive existing species (ascorbic acid- uric acid and acetaminophen) is eliminated. The usefulness of biosensor for direct glucose quantification in human blood serum matrix is also discussed. This sensor can be used as an amperometric detector for monitoring oxidase based biosensors. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.
Publication Date: 2007
Biosensors and Bioelectronics (09565663)22(12)pp. 3146-3153
For the first time glucose oxidase (GOx) was successfully co-deposited on nickel-oxide (NiO) nanoparticles at a glassy carbon electrode. In this paper we present a simple fabrication method of biosensor which can be easily operated without using any specific reagents. Cyclic voltammetry was used for electrodeposition of NiO nanoparticle and GOx immobilization. The direct electron transfer of immobilized GOx displays a pair of well defined and nearly reversible redox peaks with a formal potential (E0′) of -0.420 V in pH 7 phosphate buffer solution and the response shows a surface controlled electrode process. The surface coverage and heterogeneous electron transfer rate constant (ks) of GOx immobilized on NiO film glassy carbon electrode are 9.45 × 10-13 mol cm-2 and 25.2 ± 0.5 s-1, indicating the high enzyme loading ability of the NiO nanoparticles and great facilitation of the electron transfer between GOx and NiO nanoparticles. The biosensor shows excellent electrocatalytical response to the oxidation of glucose when ferrocenmethanol was used as an artificial redox mediator. Furthermore, the apparent Michaelis-Menten constant 2.7 mM, of GOx on the nickel oxide nanoparticles exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. In addition, this glucose biosensor shows fast amperometric response (3 s) with the sensitivity of 446.2 nA/mM, detection limit of 24 μM and wide concentration range of 30 μM to 5 mM. This biosensor also exhibits good stability, reproducibility and long life time. © 2007 Elsevier B.V. All rights reserved.
Publication Date: 2006
Electrochemistry Communications (13882481)8(9)pp. 1499-1508
Hemoglobin (Hb) was successfully immobilized on a glassy carbon electrode modified with nickel oxide (NiO) nanoparticles. The electrodeposition of metallic nickel was carried out using cyclic voltammetry (20 scans between 1 and -1.0 V at a scan rate of 50 mV s-1) in pH 4 acetate buffer solution containing 1 mM nickel nitrate. Then, the electrode was immersed in fresh phosphate solution containing 5 mg ml-1 hemoglobin and the potential was repetitively cycled (30 scans) from 1 to -0.5 V at a scan rate of 100 mV s-1 for electrodissolution and passivation of nickel oxide layer and immobilization of hemoglobin. The presence of pair of well defined and nearly reversible CV peaks at about -0.07 V vs. reference electrode (pH 7) indicates the character of Hb heme Fe(III)/Fe(II) redox couple. The formal potentials of Hb in nickel oxide film was linearly varied in the range 2-11 with a slope of 58 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The surface coverage of Hb immobilized on nickel oxide film glassy carbon electrode was about 1.73 × 10-11 mol cm-2. The transfer coefficient (α) was calculated to be 0.45 and the heterogeneous electron transfer rate constant (ks) was 5.2 ± 0.5 s-1, indicating great facilitation of the electron transfer between Hb and nickel oxide nanoparticles deposited on the electrode surfaces. The modified electrode shows excellent electrocatalytic activity toward hydrogen peroxide reduction. The Michaelis-Menten constant KM of 1.37 mM indicates that the Hb immobilized on to nickel oxide film retained its native activity. According to the direct electron transfer property and enhanced activity of Hb in nickel oxide film, it can be used as a new type of regretless biosensor without using any electron transfer mediator or specific reagent. © 2006 Elsevier B.V. All rights reserved.
Publication Date: 2006
Electroanalysis (10400397)18(7)pp. 703-711
A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes (CNTs) and thionin. Abrasive immobilization of CNTs on a GC electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes, then immersing the GC/CNTs-modified electrode into a thionin solution (electroless deposition) for a short period of time (5-50 s for MWCNTs and 5-120 s for SWCNTs ). Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range 2-12. The electrochemical reversibility and stability of modified electrode prepared with incorporation of thionin into CNTs film was compared with usual methods for attachment of thionin to electrode surfaces such as electropolymerization and adsorption on the surface of preanodized electrodes. The formal potential of redox couple (E°′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of thionin immobilized on CNTs glassy carbon electrode was approximately 1.95 × 10-10 mol cm-2 and 3.2 × 10-10 mol cm-2 for MWCNTs and SWCNTs, respectively. The transfer coefficient (α) was calculated to be 0.3 and 0.35 and heterogeneous electron transfer rate constants (Ks) were 65 s-1 and 55 s-1 for MWCNTs/thionin and SWCNTs/thionin- modified GC electrodes, respectively. The results clearly show a great facilitation of the electron transfer between thionin and CNTs adsorbed on the electrode surface. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of electrodes. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.
Publication Date: 2005
Analytical Biochemistry (00032697)344(1)pp. 16-24
The direct voltammetry and electrocatalytic properties of catalase, which was adsorbed on the surface of multiwall carbon nanotubes (MWCNTs), was investigated. A pair of well-defined and nearly reversible cyclic voltammetry peaks for Fe(III)/Fe(II) redox couple of catalase adsorbed on the surface of MWCNTs at approximately -0.05V versus reference electrode in pH 6.5 buffer solution, indicating the direct electron transfer between catalase and electrode. The surface coverage of catalase immobilized on MWCNTs glassy carbon electrode was approximately 2.4 × 10-10 mol cm-2. The transfer coefficient (α) was calculated to be 0.4, and the heterogeneous electron transfer rate constant was 80 s-1 in pH 7, indicating great facilitation of the electron transfer between catalase and MWCNTs adsorbed on the electrode surface. The formal potential of catalase Fe(III)/Fe(II) couple in MWCNTs film had a linear relationship with pH values between 2 and 11 with a slope of 58 mV/pH, showing that the electron transfer is accompanied by single proton transportation. Catalase adsorbed on MWCNTs exhibits a remarkable electrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The value for calculated Michaelis-Menten constant (1.70 mM) was high, indicating the potential applicability of the films as a new type of reagentless biosensor based on the direct electrochemistry of the catalase enzyme. © 2005 Elsevier Inc. All rights reserved.
