A new technique for measuring the temporal characteristics of the carbon fibre microelectrodes in in vivo voltammetry at millisecond time intervals

A common approach to test the time-response of carbon fibre microelectrodes entails the use of a flow injection system which allows delivery of a bolus of test compound in the flow stream to a detector electrode. The introduced bolus is distorted from its original form by convective and dispersive forces during the period of transport from the injector to the detector electrode in the connection tubing and couplings. Thus, the flow injection system allows one to change the medium in the vicinity of the electrode in about 100-200 ms. We describe here a simple falling drop system, which is an easy to use for calibration of the carbon fibre microelectrodes with respect to their sensitivity and time-response. This system does not have a loop injector and minimizes problems associated with convective and dispersive bolus distortion. It allows one to change the medium in the vicinity of the electrode in less than 10 ms. With this system, the sensitivity and the temporal resolution of the electrodes may be easily and rapidly estimated in a single experiment. The temporal resolution of the untreated, uncoated carbon fibre cylinder electrode of 300 microns tip length in response to dopamine was estimated as 1.49 +/- 0.1 microM/ms (M +/- SEM, n = 36, rise) and 0.051 +/- 0.003 microM/ms (n = 36, wash-out) on the half of amplitude of electrochemical response which was monitored by constant potential amperometry.