Polypyrrole , immobilization matrix

A direct electron transfer from entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) to a Pt electrode, via chains of the polypyrrole, acting as immobilization matrix, was demonstrated [152]. QH-ADH is able to translocate in a fast inner-enzymatic reaction, the electrons primarily accepted by PQQ to heme units located close to the outer protein shell, from where they can be transferred on the conducting-polymer chains (Fig. 13). A similarity between the electron-transfer pathway in multicofactor proteins and that of mediator-modified electroenzymes is apparent, if one considers that a multicofactor enzyme can be regarded as a combination of a primary redox site and protein-integrated electron-transfer relays. 

Almost all the FDH molecules on the electrode surface seemed to retain the enzyme activity because of the mild immobilization at less extreme potential. The enzyme activity of immobilized FDH was dependent on the thickness of polypyrrole membrane because a thicker membrane could prevent the enzyme substrate from diffusing into the membrane matrix. Therefore, it was very important to make the polypyrrole membrane as thin as possible to minimize the effect on substrate diffusion and to ensure the complete coverage of the enzyme layer. 

Polypyrrole has the potential to provide an effective method for reagentless transduction by immobilization of the ssDNA probe within the polymer matrix. Significant differences in the impedance profile of ssDNA and dsDNA have been demonstrated [59]. The differences in the impedance profile are purportedly based on intercalation differences of the polymer with ssDNA compared to dsDNA. The exact mechanism for impedimetric change resulting from conducting polymer films has not been identified, although it is likely linked, much like the impedimetric response of pure DNA, to the change in ion density that accompanies the double strand compared to the... 

In recent years the electrochemistry of the enzyme membrane has been a subject of great interest due to its significance in both theories and practical applications to biosensors (i-5). Since the enzyme electrode was first proposed and prepared by Clark et al. (6) and Updike et al. (7), enzyme-based biosensors have become a widely interested research field. Research efforts have been directed toward improved designs of the electrode and the necessary membrane materials required for the proper operation of sensors. Different methods have been developed for immobilizing the enzyme on the electrode surface, such as covalent and adsorptive couplings (8-12) of the enzymes to the electrode surface, entrapment of the enzymes in the carbon paste mixture (13 etc. The entrapment of the enzyme into a conducting polymer has become an attractive method (14-22) because of the conducting nature of the polymer matrix and of the easy preparation procedure of the enzyme electrode. The entrapment of enzymes in the polypyrrole film provides a simple way of enzyme immobilization for the construction of a biosensor. It is known that the PPy-... 

When constructing biosensors, which are to be used continuously in vivo or in situ, maintaining sensor efficiency while increasing sensor lifetime are major issues to be addressed. Researchers have attempted various methods to prevent enzyme inactivation and maintain a high density of redox mediators at the sensor surface. Use of hydrogels, sol-gel systems, PEI and carbon paste matrices to stabilize enzymes and redox polymers was mentioned in previous sections. Another alternative is to use conductive polymers such as polypyrrole [123-127], polythiophene [78,79] or polyaniline [128] to immobilize enzymes and mediators through either covalent bonding or entrapment in the polymer matrix. Application to various enzyme biosensors has been tested. 

The next most obvious applications of conducting polymers utilize their conductivity and electroactivity. Conducting polymers such as polypyrrole are readily oxidized and reduced, according to the reaction in Figure 1.5, in cases where the counterion is able to freely leave the CEP matrix and is immobilized within the CEP matrix. 

Khan, G. F. Kobatake, E. Ikariyama, Y. Aizawa, M. Amperometric biosensor with pqq enzyme immobilized in a mediator-containing polypyrrole matrix. Anal. Chim. Acta 1993, 281, 527—533. 

---