Electrochemical biosensors, polymeric

Xiang L, Zhang ZN, Yu P et al (2008) In situ cationic ring-opening polymerization tmd quatemization reactions to confine ferricyanide onto carbon nanotubes a general approach to development of integrative nanostructiued electrochemical biosensors. Antil Chem 80 ... 

The interest in chemically modified electrodes that developed during the 1980s resulted in the synthesis of many redox-active polymers and surface-confined redox couples, including ferrocenes. These were subsequently adapted to electrochemical biosensors, and both surface-confined and polymeric ferrocenes have been widely used. Typically, polymeric ferrocenes that have been exploited in this way include poly(vinyl) ferrocenes, polysiloxanes, polyethylene oxide with covalently attached ferrocenes, poly(allylamine) ferrocene, and polacrylamide ferrocene cross-linked hydrogels." ... 

Active enzymes were encapsulated into a sol-gel matrix for the first time in 1990 719 About 60 different types of hybrid bioceramic materials with inotganic matrices made from silicon, titanium, and zirconium oxides Ti02-cellulose composites etc. were described. Recentiy, bioceramic sensors, solid electrolytes, electrochemical biosensors, etc. have been surveyed in a review. The moderate temperatures and mild hydrolytic and polymerization conditions in sol-gel reactions of alkoxides make it possible to trap proteins during matrix formation. This prevent proteins denaturation. The high stability of the trapped biomolecules, the inertness, the large specific surface, the porosity, and the optical transparency of the matrix facilitate use of sol-gel immobilization. The principal approaches ate considered below. 

Another application of pH-responsive polymers was shown by de Groot et al. (2013), as shown in Figure 5.11. Surface-initiated atom transfer radical polymerization synthesized PMAA brushes were used to create pH-responsive nanoporous platforms. It was shown that at pH 4, gating of ions was allowed through the nano channels, whereas at pH 8, the pores were closed. The authors predict that their pH-re-sponsive channels have potential as electrochemical biosensors and in bioseperation technology. 

Pilloton R, Mela J, Marradini L (1999) Screen printed electrochemical biosensors on ceramic and polymeric substrates. Advances in science and technology solid state chemical and biochemical sensors, vol. 26, pp. 501-507. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Horseradish peroxidase (HRP) is an extracellular plant enzyme that acts in regulation of cell growth and differentiation, polymerization of cell wall components, and the oxidation of secondary metabolites essential for important pathogenic defense reactions. Because of these essential functions, and also because of its stability and ready availability, HRP has attracted considerable attention.13 It has been involved in a number of applications, such as diagnostic assays,14 biosensors,15 bioremediation,16 polymer synthesis,17 and other biotechnological processes.18 More applications in which HRP catalysis is translated into an electrochemical signal are likely to be developed in the near future. 

The use of nanoparticles has extended throughout the field of biosensors in the electrochemical detection of DNA and immunoreactions (Murphy 2006). A wide range of nanoparticles including nanotubes and nanowires, prepared from metals, semiconductor, carbon or polymeric species, have been investigated. The enhanced electrochemistry is due to the ability of the small nanoparticles to reduce the distance between the redox site of a protein and the electrode, since the rate of electron transfer is inversely dependent on the exponential distance between them (Balasubramanian and Burghard 2006). CNT-modified electrodes have been most frequently used for the development of biosensors (Gooding 2005). 

Enzyme biosensors containing pol3mieric electron transfer systems have been studied for more than a decade. One of the earlier systems was first reported by Degani and Heller [1,2] using electron transfer relays to improve electrochemical assay of substrates. Soon after Okamoto, Skotheim, Hale and co-workers reported various flexible polymeric electron transfer systems appUed to amperometric enz5une biosensors [3-16], Heller and co-workers further developed a concept of wired amperometric enzyme electrodes [17—27] to increase sensor accuracy and stability. 

Cosnier, S. (1999) Biomolecule immobilizahon on electtode surfaces by entrapment or attachment to electrochemically polymerized films. A review. Biosensors ic Bioelectronics, 14 (5), 443 456. 

In this chapter, we focus on the use of the continuous resonance QCM and EQCM devices to study enzymatic polymerization reactions, biochemical and biomimetic processes and to create thin polymer films electrochemically on the QCM electrode surface. We describe some QCM applications of thin polymer films in enzyme electrode and other biosensors and briefly describe specific cell binding systems to create whole cell biosensors. 

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