Ferrocene modified glucose oxidase

Fig. 13 Self-assembled linkage of ferrocene-modified glucose oxidase (GOD) on thiol monolayer...

Fig. 14 Cyclic voltammograms of ferrocene-modified glucose oxidase with (—) and without (—) glucose...

Substrate concentration dependence of response current of the gold-black electrode was compared with that of gold disk electrode. The ferrocene-modified glucose oxidase which was used in this measurement had 11 ferrocenes per glucose oxidase. The electrode potential was controlled at 0.4 V vs. Ag/AgCl. The response current was recorded when the output reached at a steady state. The response current was enhanced when ferrocene-modified glucose oxidase was self-assembled on a porous gold-black electrode. 

The porous matrix of gold-black electrode has enabled ferrocene-modified glucose oxidase to perform the smooth electron transfer by means of easy access between self-assembled molecules and electrode surface. 

Schuman et al. have synthesized ferrocene-modified glucose oxidase with the ferrocene derivatives bound via long and flexible chains directly to the outer surface of the enzyme [17]. A peripherally attached redox mediator may accept electrons through either an intramolecular or through an intermo-lecular process. 

Fig.21 Glucose concentration dependence of response current on ferrocene-modified glucose oxidase self-assembledon the gold black ( ) and plain gold (0) electrodes...

The sensor is based on a ferrocene-modified glucose oxidase electrode strip. For glucose determination, a drop of blood is transferred to a disposable enzyme electrode strip, which is then inserted into a pen-sized readout instrument. The response is more rapid than that of photometric test strips. Venous as well as capillary blood may be used as sample material. There are a number of systems that measure very rapidly and require less than 1-pl sample. 

These ProDOT derivatives were polymerized and also copolymerized with EDOT electrochemically. A 1 4 copolymer of ProDOT-Me(CH20H)-R = CH2OH, = CH3 in Figure 13.8—with EDOT was grown on a platinum electrode and reacted with a solution of 4,4 -diisothiocyanatostilbene-2,2 - disul-fonic acid. Ferrocene-modified glucose oxidase was then coupled via its free... 

It is noted that the anodic peak current prominently increases with an increase in the molar ratio of ferrocene to glucose oxidase whilst the amount of enzyme self-assembled on the electrode surface is fixed as presented in Figs. 14-16. This indicates that each modified ferrocene may contribute to electron transfer between the enzyme and the electrode in the case of gold-black electrode, the ferrocene-modified enzyme could form multi electron transfer paths on the porous gold-black electrode. 

In contrast to the mediator-modified electrodes, Degani et al. modified glucose oxidase itself by means of covalently bound ferrocene [4]. After modifying enzymes with ferrocene carboxylic acid, they observed direct electron transfer from the active site of the enzyme to a gold or platinum... 

This electron transfer was positively affected by the immobilization of glucose oxidase on glassy carbon modified by aminophenyl boronic acid [193] or adsorption on to metalized carbons [194]. Nevertheless, it was possible to achieve good electron transfer only by modification ( functionalization ) of the enzyme with redox compounds (ferrocene derivatives). The direct electrical communication between the modified enzyme and an electrode has been proved by cyclic voltammetry. Thus attention was paid to the construction of various types of modified glucose oxidase electrodes. For instance, Benneto et al. [195] describe an... 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

P.C. Pandey, S. Upadhyay, N.K. Shukla, and S. Sharma, Studies on the electrochemical performance of glucose biosensor based on ferrocene encapsulated ORMOSIL and glucose oxidase modified graphite paste electrode. Biosens. Bioelectron. 18,1257—1268 (2003). 

In contrast to the molecular wire of molecular interface, electron mediators are covalently bound to a redox enzyme in such a manner as an electron tunneling pathway is formed within the enzyme molecule. Therefore, enzyme-bound mediators work as molecular interface between an enzyme and an electrode. Degani et al. proposed the intramolecular electron pathway of ferrocene molecules which were covalently bound to glucose oxidase [ 4 ]. However, few fabrication methods have been developed to form a monolayer of mediator-modified enzymes on the electrode surface. We have succeeded in development of a novel preparation of the electron transfer system of mediator-modified enzyme by self-assembly in a porous gold-black electrode as schematically shown in Fig.12 [14]. 

To overcome the poor stability of ferrocene-mediated enzyme sensors, mediator-modified electrodes have been used. In the case of glucose oxidase, the cofactor FAD is deeply buried within the protein matrix. The depth of the active center is estimated to be 0.87 nm. Therefore, one cannot expect that the mediator covalently attached to the electrode surface via a short spacer retain the possibility of closely approaching the cofactor of the enzyme. 

Amperometric glucose Ferrocene-modified polyallylamine (PAFi-Fc) Glucose oxidase (GOx) (77)... 

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

Figure 4. (left) Steady state response to 31.5 mM glucose of the ferrocene-modified poly(siloxane) / glucose oxidase / carbon paste electrodes at several applied potentials. The relay systems are indicated next to each curve, which is the mean result for four electrodes. 

Figure 8. (right) Glucose calibration curves for the ferrocene-modified poly(ethylene oxide)/glucose oxidase/carbon paste electrodes at E =... 

An example of this analysis is a modified quartz crystal with a (poly(allyI-amine)-ferrocene hydrogel crosslinked with Glucose Oxidase and immersed in liquid electrolyte which has been studied by electroacoustic... 

---