Golam Faruque Khan

Electrochemical behaviour of monolayer quinoprotein adsorbed on the electrode surface

Abstract Direct electron transfer between a monolayer of quinoprotein oxidoreductase, fructose dehydrogenase (FDH) and various electrodes such as Pt, Au and GC was investigated. To achieve direct and reversible electron transfer, monolayer FDH was prepared on these electrodes by a voltage-assisted adsorption method. The monolayer preparation depended on the applied potential, the adsorption time, the pH of the incubation medium and the protein concentration. The electron transfer between adsorbed FDH and the electrode proceeded directly and reversibly at all the electrodes. The redox potentials of FDH at pH 4.5 were 80, 80 and 40 mV (vs. Ag/AgCl) for the Pt, Au and GC electrodes, respectively. This electrochemical property depended on the electrode material, i.e. one electrode retained the enzyme with more enzyme activity than did the others, while another retained the enzyme with more electrochemical activity than the others. This suggests that partial orientation is possible by a particular electrode material. The mode of orientation on each metallic surface was different from that on the carbon electrode: the former provided more rapid electron transfer with lower enzyme activity, whereas the latter produced slower electron transfer with higher dehydrogenase activity. In addition, an attempt was made to determine fructose with a FDH-adsorbed electrode by detecting the direct electron transfer from the enzyme to the electrode.

Platinization of Shapable Electroconductive Polymer Film for an Improved Glucose Sensor

This paper describes a novel electrode material for the preparation of a first generation amperometric biosensor. The material consists of a flexible conductive polymer film of polypyrrole doped with polyanions and a layer of microporous Pt black, prepared electrochemically on the polymer film. Sensors fabricated with this material produce a comparatively higher H 2 O 2 oxidation current at a lower applied potential. Glucose sensors were prepared by adsorbing glucose oxidase at the porous Pt black structure, covering with gelatin, and finally cross-linking with glutaraldehyde at dry condition. The developed sensors showed significantly improved performance over similar reported sensor systems. The performance of the glucose sensor was evaluated by a specially designed flow injection analysis (FIA) system. The sensors were continuously polarized at 25°C and glucose samples were automatically injected at 30 min intervals. The sensors worked at 0.3 to 0.4 V and produced a huge current response (>1 mA/cm 2 ) with a wide linear range of detection (0 to 100 mM). The system effectively recycles oxygen, thus, the response current was not affected by a variation of oxygen concentration of the buffer. The interference of ascorbic acid, uric acid, bilirubin, etc. (at a physiological level) produced a current within the experimental error level. The sensor showed an extended working and shelf life.

Amperometric biosensor with PQQ enzyme immobilized in a mediator-containing polypyrrole matrix

Abstract An amperometric biosensor for fructose was fabricated by co-immobilizing a pyrrolo quinoline quinone (PQQ) enzyme (fructose dehydrogenase, FDH) with mediator in a thin polypyrrole (PP) membrane. Electron transfer between the prosthetic PQQ of FDH and the transducer electrode was promoted through a mediator-containing PP interface. Two methods of sensor preparation are described. In one, FDH was potentiostatically adsorbed as a monolayer on a transducer electrode, and a very thin (equivalent to a monolayer of FDH) PP membrane containing a mediator was electrodeposited on the adsorbed FDH. In the other, FDH and mediator [hexacyanoferrate(II) or ferrocene] were co-immobilized on an electrode by electrochemical polymerization of pyrrole. In the former instance, a highly sensitive and selective response for fructose was obtained with a wide detection range of up to 30 mM with a linear range from 10 μm to 10 mM. However, the stability of the sensor was poor owing to the easy leakage of mediator. The stability of the sensor was significantly improved in the latter instance, with a dynamic range for fructose detection from 50 μM to 5 mM.

Electrochemical oxidation and reduction of PQQ using a conducting polypyrrole-coated electrode

Abstract PQQ (pyrrolo-quinoline quinone, methoxitin) is a prosthetic group of some oxidoreductases and a growth factor for microorganisms. In this study, reversible electrochemical oxidation and reduction of PQQ were performed using a conductive polypyrrole film-coated electrode. The electrochemical oxidation and reduction of PQQ on various electrodes, such as platinum, gold and glassy carbon electrodes, were found to occur irreversibly. The electrochemical behaviour of PQQ was characterized by cyclic voltammetry and differential pulse voltammetry. Electrochemically reduced PQQ (PQQH 2 ) was observed directly by spectrophotometry. Furthermore, PQQ was entrapped efficiently into a thin polypyrrole film by electrochemical polymerization of pyrrole. The oxidoreductive properties of entrapped PQQ were also characterized.

Electronically modulated biological functions of molecular interfaced enzymes and living cells

Conducting polymer molecular interfaces have been implemented to modulate biological functions of fructose dehydrogenase, pyruvate oxidase and Saccharomyces cerevisiae at the electrode surface by adjustment of electrode potential. The enzyme activity of the polypyrrole-interfaced fructose dehydrogenase was electronically modulated by means of electron transfer between the enzyme and the electrode surface. The enzyme activity of polypyrrole-interfaced pyruvate oxidase was modulated by an electronically driven change of substrate concentration. The gene expression in polypyrrole-interfaced Saccharomyces cerevisiae was electronically induced by a change in the phosphate concentration.

Molecular wire and interface for bioelectronic molecular devices

Protein molecules have successfully been incorporated in bioelectronic molecular devices through the molecular wire or interface of conducting polymer. Such enzymes as glucose oxidase and fructose dehydrogenase were adsorbed on the platinum electrode surface, which was followed by the electropolymerization of pyrrole to deposit an ultimately thin layer of polypyrrole on the electrode surface. Alcohol dehydrogenase was immobilized in a polypyrrole membrane with NAD and Meldora’s blue in the similar manner on the electrode surface. The electron transfer from the electron transfer sites of these enzymes to the corresponding electrode has been promoted through the molecular wire. It has been demonstrated that the enzyme activity is modulated by changing the potential of the electrode with which the enzyme is connected through the molecular wire. On the basis of the electronic characteristics of these enzyme proteins the design principles of biomolecular electron devices have been proposed.