ABSTRACT
Chemical sensors are those that use chemical processes in the recognition and transduction steps. Gas-sensing membrane sensor "electrodes" are not single electrodes, but are combination electrodes with a base indicating electrode and an external reference electrode combined into one unit. Membranes of Teflon, silicon rubber, and polyethylene can be used because they are oxygen permeable, but not ion permeable. Enzyme substrate electrodes are sensors in which an ion-selective electrode is covered with a coating containing an enzyme that causes the catalytic reaction of an organic or inorganic substance to produce a species to which the electrode responds. In contrast with the layered structure of gas-sensing ion-selective electrodes, the enzyme sensors originally used a single immobilized coating on a glass pH electrode or monovalent cation-sensing electrodes. Operationally, the enzyme-based-sensor combinations for substrate analysis involve interposing the enzyme system between the test solution and the species-selective electrode. Biosensors are a subsection of chemical sensors that use biological recognition processes.
