Enzyme-modified electrodes

Figure 62.2 illustrates an experimental setup for biosensor measurements. Electrochemical measurements using biosensors require three electrodes, which are called the working electrode (enzyme-modified electrode), reference electrode, and counter electrode. In some cases, the three electrodes can be assembled into a single-body electrode. It is also possible to eliminate the reference electrode and use the counter electrode as a pseudoreference electrode for specific reasons, such as miniaturization. The experimental setup shown in Figure 62.2 is a batch system, in which the electrodes are immersed in the sample solution to obtain an output signal. For constructing flow systems, the electrodes are set at a... 

Electrocatalysis for Fuel Cells at Enzyme-Modified Electrodes... 

ELECTROCATALYSIS FOR FUEL CELLS AT ENZYME-MODIFIED ELECTRODES... 

Sulfite modified enzyme electrode. (2) L-Lactate/L-malate/ sulfite multibiosensor L-lactate dehydrogenase/L-malate dehydrogenase/ sulfite oxidase surface-modified enzyme electrodes/enzymes were deposited on the composite electrodes and covered with a dialysis membrane ... 

Regarding the drying time, the enzyme-modified electrodes dried for 30 min provided higher absorbance values than the ones dried for 22 h. Hence, short drying times were enough to immobilise the enzyme and longer times only accelerated the enzyme inactivation. At this stage it is... 

Wash the biosensor with a large volume of phosphate buffer. The enzyme-modified electrodes prepared in this way remain active for more than 1 month, when stored at 4°C. 

Lowry JP, O Neill RD. Homogeneous mechanism of ascorbic acid interference in hydrogen peroxide detection at enzyme-modified electrodes. Analytical Chemistry 1992, 64, 453 156. 

Electrochemical Behavior of PPy-GOD Film Electrode with Pharmaceutical Drugs. Although the chemically modified electrode has been developed for more than a decade, and many kinds of materials have been used for the modification of the electrode surface, the enzyme modified electrode has rarely been used for the study of electroactive species. This is probably due to the fact that the enzyme is not electronically conductive and also it is difficult to immobilize an enzyme on the electrode surface. So far, biological lipids have been used to modify the electrode, and the modified electrode shows a selectivity for hydrophobic molecules because the lipid molecule is hydrophobic (37-39). 

Hale et al. reported the use of an enzyme-modified carbon paste for the determination of acetylcholine [21], The sensor was constructed from a carbon paste electrode containing acetylcholineesterase and choline oxidase, and the electron transfer mediator tetrathiafulvalene. The electrode was used for the cyclic voltammetric determination of acetylcholine in 0.1 M phosphate buffer at +200 mV versus saturated calomel electrode. Tetrathiafulvalene efficiently re-oxidized the reduced flavin adenine dinucleotide centers of choline oxidase. The calibration graph was linear up to 400 pM acetylcholine, and the detection limit was 0.5 pM. 

All electrodes react with their environment via the surfaces in ways which will determine their electrochemical performance. Properly selected surface modification can effectively enhance the electrode heterogeneous catalysis property, especially selectivity and activity. The bulk materials can be chosen to provide mechanical, chemical, electrical, and structural integrity. In this part, several surface modification methods will be introduced in terms of metal film deposition, metal ion implantation, electrochemical activation, organic surface coating, nanoparticle deposition, glucose oxidase (GOx) enzyme-modified electrode, and DNA-modified electrode. 

Su, L., Qiu, X. P., Guo, L. H., Zhang, F. H. and Tung, C. H. (2004), Amperometric glucose sensor based on enzyme-modified boron-doped diamond electrode by cross-linking method. Sensor Actuator B, 99(2-3) 499-504. 

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