ENZYME-MODIFIED MICROELECTRODES FOR IN-VIVO NEUROCHEMICAL MEASUREMENTS

Various approaches to the production of miniaturized chemical sensors for in vivo applications are reviewed with special regard to the measu rement of chemical transients ih the mammalian brain. The basic tenant s of biosensor principles are discussed in terms of the temporal respo nse of enzyme-modified electrodes and selection of redox enzymes. The effects of electron transfer mediators and differential measurements t o gain selectivity are also examined. A broad range of immobilization methods including membrane entrapment, physical and chemical adsorptio n, cross-linking agents, polymeric entrainment, electropolymerized fil ms and covalent derivatization are examined. The use of polymer layers and redox polymers to gain selectivity are discussed. The discussion is limited to microelectrode surfaces (< 100 mu m diameter) and variou s electrode types are examined, including bare and platinized carbon f ibers, platinum microelectrodes, conducting organic salts and carbon p aste electrodes.