Enzyme modified amperometric sensors for choline and acetylcholine with tetrathiafulvalene tetracyanoquinodimethane as the electron-transfer mediator

To understand more about acetylcholine, an important neurotransmitter, and its precursor choline, acetylcholine and choline amperometric sensors have been fabricated. The performance of the sensors has been improved so that measurements of choline and acetylcholine have a high sensitivity and selectivity. The sensor is constructed from a bevelled and recessed carbon-fiber microelectrode with a radius of 16.5 mu m. An organic conducting salt, tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ), is employed as an electron-transfer mediator. A recess at the tip of the microelectrode was partially filled with TTF-TCNQ and covered with cross-linked choline oxidase and acetylcholine esterase. A thin Nafion polymer was also coated to increase the electrodes' mechanical stability. The resulting acetylcholine and choline sensors have a response time of 8.2 s and a linear range up to 50 and 100 mu M respectively. Interference from the electroactive compounds ascorbic acid, uric acid, dopamine, 5-hydroxytryptamine (5-HT), and DOPAC was low at their maximal physiological concentrations. Data obtained in slices of rat brain indicate that these sensors are a useful and practical means of monitoring choline concentration changes in the rat brain microenvironment.