Carbon enzyme-modified

The large size of redox enzymes means that diffusion to an electrode surface will be prohibitively slow, and, for enzyme in solution, an electrochemical response is usually only observed if small, soluble electron transfer mediator molecules are added. In this chapter, discussion is limited to examples in which the enzyme of interest is attached to the electrode surface. Electrochemical experiments on enzymes can be very simple, involving direct adsorption of the protein onto a carbon or modified metal surface from dilute solution. Protein film voltammetry, a method in which a film of enzyme in direct... 

J. Wang and X. Zhang, Screen printed cupric-hexacyanoferrate modified carbon enzyme electrode for single-use glucose measurements. Anal. Lett. 32, 1739-1749 (1999). 

To obtain optimum response conditions for the biosensor based on carbon paste modified with polyphenol oxidase of jack fruit (A. in-tegrifolia L.) crude extract, the effect of graphite powder, fatty acids, and the enzyme concentrations were studied. The scan rate, pulse amplitude, and pH were also investigated. Table 23.1 summarizes the range over which each variable was studied and the optimal value found in those studies. 

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. 

The studies of the composition and state of chemical elements on enzyme-modified wool surfaces (carbon, nitrogen, oxygen, sulphur) as compared to untreated ones were performed by means of XPS analysis (Vacuum System Workshop Ltd., England) using non-monochromatized AlKa radiation with energy 1486.6 eV, 10 kV and 200 W. The base pressure in the analysis chamber was 3 x 10-6 Pa [30], XPS spectra were acquired in the constant analyser transmission mode with energy of electron transmission 22 eV. 

The use of a carbon paste electrode (CPE) incorporating tyrosinase (see Section VI.A.2) as ELD for LC determination of phenols was investigated. The enzyme-modified electrode showed higher stability than the unmodified one °. ... 

The degradation of cholesterol leads to the production of bile acids which are structurally closely related to various steroid hormones. (3-Hydroxysteroid dehydrogenase (EC 1.1.1.51) catalyzes the NAD+-de-pendent oxidation of 3(3-, 17(3- and some l6(3-hydroxysteroids to the respective ketosteroids. The enzyme has been adsorbed on a carbon electrode modified by NMP+TCNQ and the NADH liberated in the reaction oxidized anodically (Albery et al., 1987a). Campanella et al. (1984) employed an enzyme sequence electrode composed of NAD+-de-pendent steroid dehydrogenase and horseradish peroxidase for assay of 7a-hydroxysteroids. 

PN Bartlett, D Pletcher, J Zeng. Approaches to the integration of electrochemistry and biotechnology. 1. Enzyme-modified reticulated vitreous carbon electrodes. J Electrochem Soc 144 3705-3710, 1997. 

Figure 6.8 The scheme used by Pantano and Kuhr to attach glutamate dehydrogenase to the surface of a carbon fiber. Step 1, after electrochemical oxidation of the fiber to produce surface oxygen functionalities, a diamine is attached to the surface using carbodiimide coupling. Step 2, biotin is attached to the other end of the diamine. Step 3, the bound biotin is reacted with avidin to form a biotin-avidin complex attached to the carbon surface. Step 4, biotinylated enzyme is complexed to the avidin to complete construction of the enzyme modified carbon fiber surface. (Adapted from [27].)...

Razumas VJ, Jasaitis JJ, Kulys JJ. 700-Electrocatalysis on enzyme-modified carbon materials. Bioelectrochem Bioenerg 1984 12 297-322. 

Various chemically modified electrode configurations have been investigated to optimize the current response and lower the overpotential. A hypox-anthine biosensor has been reported based on a glassy carbon paste electrode modified with Au nanoparticles and XO. The enzyme modified electrode shows catalytic activity at +500 mV vs. Ag/AgCl, which is 250 mV less positive than in the absence of the Au nanoparticles. Pundir and coworkers have extensively studied an XO-based biosensor with several nanomaterials and xanthine concentrations were determined by the measurement of H2O2 produced at +600 mV vs. Ag/AgCl. The biosensor was used for quantification of xanthine in tea leaves, coffee powder and fish meat. 

Diaz-Diaz et al., 2011 describes an electrochemical sensors based on a catalytic 2,4,6-trichlorophenol molecularly imprinted microgel that rnirnics the dehalogenative function of the natural enzyme chlorofjeroxidase for p>-halophenols. Two strategies were explored a carbon paste modified with the polymer and the drop)-coating of screen-fainted electrodes with powder suspensions of the polymer and carbon nanotubes. With this last design, 2,4,6-trichlorophenol concentrations above 25 mM could be detected. 

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