Amperometric enzyme electrodes.

Three different types of amperometric enzyme electrode are described. The first type uses a conducting organic-salt electrode to oxidize NADH. Results for sensors for ethanol and for bile acids are presented. In the second type of sensor, flavoenzymes are directly oxidized on the surface of the conducting organic-salt electrode. Results for five different enzymes are described. The mechanism of the enzyme oxidation is discussed and the reaction is shown to take place by heterogeneous redox catalysis and not by homogeneous mediation. The enzymes are strongly adsorbed on the electrode; microelectrodes for in vivo studies can be constructed without a membrane. Results for in vivo studies of changing glucose levels in the brain of a freely moving rat are presented. The third type of sensor is designed to measure low levels of toxic gases such as H2S and HCN. This is done by monitoring the inhibition by the toxic gas of the activity of the respiratory enzyme cytochrome oxidase.