Search

Glucose oxidase (GOx) is an enzyme, which is used for the development of enzymatic biofuel cells. Therefore in this research redox competition mode of scanning electrochemical microscopy (RC-SECM) was applied for the investigation of glucose oxidase (GOx) catalyzed reaction kinetics. The GOx was immobilized by glutaraldehyde on substrates of different electrical conductivity: (i) gold covered glass was used as conducting substrate and (ii) plastic poly(methyl methacrylate) was used as non-conducting substrate. Current vs distance dependencies were registered by SECM at different concentrations of glucose in the absence of redox mediator. The potential of −750 mV vs Ag/AgCl(3 M KCl) was applied to the microelectrode (ME), which was used as a probe in SECM, in order to register oxygen reduction current. Consumption of oxygen by the GOx based layer was evaluated according to principles determined by Michaelis-Menten kinetics. Apparent Michaelis constants KM(app.) were calculated from the dependencies of current vs glucose concentration. In both these cases the KM(app.) value increased when the distance between ME and enzyme modified surface was increasing from 10 to 30 μm, while the KM(app.) value decreased by increasing the distance from 30 to 60 μm.

Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy-layer formation and the linear interval was extended up to 19.9 mmol L−1 after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM−1 cm−2, the limit of detection – 0.20 mmol L−1. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples.

This study describes the evaluation of histamine imprinted polypyrrole deposited on boron doped nano- crystalline diamond (NCD). Boron doped oxygen termi- nated NCD (B : NCD) was used as a conducting substrate for the design of here reported electrochemical sensor. Some peculiarities of B : NCD were evaluated and oxida- tion kinetics of both NCD and B : NCD was investigated. Both the NCD and B : NCD were modified by molecular- ly imprinted polypyrrole and not-imprinted polypyrrole. Histamine was used as a template for molecular imprint- ing of polypyrrole. Electrochemical impedance spectros- copy was applied for the evaluation of formed MIP and NIP layers.

The influence of redox mediators (tetrathiafulvalene (TTF), tetrathiafulvalene-tetracyanoquinodimethane complex (TTF-TCNQ), phenazine methosulfate (PMS), 5,6-diamino-1,10-phenonthroline (5,6-DAP), potassium ferrocyanide (K4[Fe(CN)6]), methylene blue (MB) and toluidine blue (TB)) on the response of amperometric glucose biosensor was investigated in this research. Graphite rod electrode (GRE) modified by adsorbed mediator and glucose oxidase (GOx) cross-linked with glutaraldehyde was served as working electrode. The highest amperometric signals were observed by using TTF and TTF-TCNQ as mediators. The impact of amount of immobilized GOx, an optimal pH region for operation, stability and reproducibility of the analytic signal of designed biosensor using these mediators were investigated and discussed.

A single compartment biofuel cell (BFC) based on an anode and a cathode powered by the same fuel glucose is reported. Glucose oxidase (GOx) from Aspergillus niger was applied as a glucose consuming biocatalyst for both anode and cathode of the BFC. The 5-amino-1,10-phenanthroline modified graphite rod electrode (GRE) with cross-linked GOx was used as the bioanode, and the GRE with co-immobilised horseradish peroxidase and GOx was exploited as the biocathode of the BFC. The open-circuit voltage of the designed BFC exceeded 450 mV and a maximal power density of 3.5 µW/cm2 was registered at a cell voltage of 300 mV.

A self-assembled monolayer (SAM) modified by 4-formylphenylboronic acid was formed on the gold electrode, which was applied for the determination of trace concentrations of Cu(II). The formation of advanced SAM on the gold electrode was evidenced by electrochemical impedance spectroscopy, atomic force microscopy and contact angle measurements. Electrochemical determination of Cu(II) ions was performed by square wave voltammetry. Some mutual interferences caused by Cd(II), Co(II), Fe(II), Ni(II) and Pb(II) ions were investigated and it was demonstrated how the negative effects of these interfering ions could be eliminated by adjustment of proper parameters of square wave voltammetry.

A newly isolated, purified, and characterized PQQ-dependent alcohol dehydrogenase (a bacterial membrane-bound protein) was recently found to display a surprisingly large linear range and high selectivity towards ethanol when integrated into a conducting polymer network on a platinum electrode. These findings motivated us to study the enzyme when simply immobilized onto carbonaceous surfaces in order to establish its characteristics and suitability for sensor development, the sensor design being based on a direct-electron transfer pathway. Graphite rods and screen-printed electrodes were modified in two different ways, and were operated both in FIA and batch mode. The obtained biosensor characteristics were highly dependent on the sensor architecture, the highest sensitivity (179 mA M-1 cm(-2)) and lowest detection limit (1 muM) being obtained for screen-printed electrodes used in a batch mode. A mechanism of the observed direct electron transfer between the enzyme's active center and the electrode is proposed. (Less)

An optimized material for the development of reagentless oxygen-independent biosensors based on conducting polymers is described. Considering the prerequisites for a fast electron transfer between a redox enzyme and the electrode surface via an electron-hopping mechanism, an Os-complex-modified pyrrole derivative with a long, flexible spacer chain has been synthesized. Copolymerization of the new mediator-modified pyrrole monomer with pyrrole was optimized aiming on a higher mediator loading in the film. The feasibility of this material for the development of reagentless oxygen-independent biosensors is demonstrated by entrapment of a PQQ-dependent glucose dehydrogenase isolated from Erwinia sp. 34-1 within this electrochemically grown redox-polymer network.

Preparation and characterization of electrodes suitable for determination of glutathione is reported in this study. For this poly-m-aminophenol (PmAP), poly-o-aminophenol, and poly-p-aminophenol were electrochemically deposited from aqueous solution on the surface of glassy carbon (GC) electrode by potential cycling in the range of +0.2–+1.0 V. The modified GC electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, contact angle measurement and ellipsometry. It was found that poly-m-aminophenol modified GC electrode (PmAP/GC-electrode) is most suitable for electroanalytical determination of glutathione. An electroanalytical system for the determination of glutathione based on the PmAP/GC-electrode was developed. The analytical system was characterized by low limit of detection, good stability, high sensitivity and wide linear detection range.