Flavin modified electrodes

Cooke and coworkers have reported preparation of flavin-modified electrodes using a similar electropolymerization procedure.34 They have also studied electrodes coated with self-assembled monolayers (SAMs) formed from both flavin39 and phenanthrenequinone disulfides.59 The monolayers are stable in CH2C12 solution, and, as with the electrodes formed from 30, show redox-dependent binding behavior similar to that seen in solution. Interestingly, the phenanthrenequinone SAM... 

Flavin adenine dinucleotide (FAD) has been electropolymerized using cyclic voltammetry. Cyclic voltammograms of poly (FAD) modified electrode were demonstrated dramatic anodic current increasing when the electrolyte solution contained NADH compare with the absence of pyridine nucleotide. 

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

ADP AFP ab as ALAT AP ASAT ATP BQ BSA CEH CK CME COD con A CV d D E E EC ECME EDTA EIA /e FAD FET FIA G GOD G6P-DH HBg HCG adenosine diphosphate a-fetoprotein antibody antigen alanine aminotranferase alkaline phosphatase aspartate aminotransferase adenosine triphosphate benzoquinone bovine serum albumin cholesterol ester hydrolase creatine kinase chemically modified electrode cholesterol oxidase concanavalin A coefficient of variation (relative standard deviation) layer thickness diffusion coefficient enzyme potential Enzyme Classification enzyme-chemically modified electrode ethylene diamine tetraacetic acid enzyme immunoassay enzyme loading factor flavin adenine dinucleotide field effect transistor flow injection analysis amplification factor glucose oxidase glucose-6-phosphate dehydrogenase hepatitis B surface antigen human chorionic gonadotropin... 

Application of poIy(AMFc) electrode. The poly(AMFc) modified electrode was used in the construction of a flavin enzyme-based biosensor. Fig. 3B shows the effect of pH on the response of the glucose electrode. This pH profile is similar to that reported in literature with a maximum at pH of around 5.5. A pH of 5.5 was therefore used for characterization of the electrode. 

Amphophilic pyrroles modified with biotin have b n used to attach a number of biotinylated oxidases and flavins to electrode surfeces by means of an avidin/biotin interaction. This approach not only avoids use of large amounts of enzyme but also r ults in a polymer with excellent swelling properties and thus improved mass transport in the polymer film 51). 

The only exception to the rhodium chemistry for the nonenzymatic electrocatalytic reduction of NAD" recalls the structure of flavins and it was demonstrated with aminopteridone derivatives [436]. In the same line, the low formal potential of neutral red (NR) and the possibility of elec-tropolymeriiation resulted in poly(NR)-modified electrodes able to regenerate NADH at —0.6 versus Ag/AgCl and pH 6 [437]. 

In the literature, several enzymatic (Kirstein et al., 1999 Cosnier et al., 1994) and nonenzymatic (Gamboa et al., 2009 Groot and Koper, 2004) electrochemical biosensors were reported for the N03 determination. The enzymatic determination of N03 using nitrate reductase (NaR)—modified electrode is novel and highly selective. NaR is a multidomain enzyme containing flavin adenine dinucleotide (FAD), two heme-Fe and molybdopterin, which catalyzes the two-electron reduction of N03 to NOa (Quan et al., 2005). 

Figure 17.12 Direct electrocatal3ftic oxidation of D-fnictose at a glassy carbon electrode painted with a paste of Ketjen black particles modified with D-fructose dehydrogenase from a Gluconobacter species. The enzyme incorporates an additional heme center allowing direct electron transfer from the electrode to the flavin active site. Cyclic voltammograms were recorded at a scan rate of 20 mV s and at 25 + 2 °C and pH 5.0. Reproduced by permission of the PCCP Owner Societies, from Kamitaka et al., 2007.

Au NPs (1.2 nm) that include a single /V-hydroxysuccinimide-active ester functionality were modified with 2-amino-ethyl-flavin adenine dinucleotide, (5), and apo-glucose oxidase was reconstituted on the FAD cofactor units to yield the Au NP-GOx hybrid (Fig. 12.6a). The resulting hybrids were linked to the Au surface by different dithiol bridging units (8), (9), and (10). The resulting NP-functionalized glucose oxidase, GOx, exhibited electrical contact with the electrode surface, and the Au NPs... 

This is illustrated in Figure 6A, where it is clear that different E° values are found depending on whether the redox compound is in a soluble or in an adsorbed state and also depending on the nature of the surface on which the compounds is adsorbed. That these observations are not the results of local pH effects at the electrode surface is revealed by comparing the variation of the E° of an adsorbed flavin with that of the soluble form (103). As is clear in Figure 6B, the E° values for both the adsorbed and soluble formes of the flavin are very close up to about pH 6 where they start to differ because of a pl -shift of the adsorbed flavin. These observations indicate the close interaction between the electrode surface and the adsorbed modifier. 

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. 

Fig. 1.12. Schematb drawing of the glucose oxidase molecule, showing the electron-transfer distances involved in the various steps of moving an electron from its two flavin adenine dinucleotide/reduced flavin adenine dinucleotide (FAD/FADHg) centers to a metal electrode. Left The enzyme before modification. Right The modified enzyme, after chemical attachment of an array of electron transfer relays ( R ). (Reprinted from Y. Degani and A. Heller, J. Phys. Chem. 91 1286, 1987.)...

---