Fast cyclic voltammetry: improved sensitivity to dopamine with extended oxidation scan limits.

Fast cyclic voltammetry at carbon fibre microelectrodes has been used in vitro and in vivo mainly to monitor the release and uptake of dopamine. The 'standard' input voltage waveform (-1000 to +1000 mV, vs. Ag/AgCl, 300 V/s scan rate) has a lower limit of detection for dopamine of about 200 nM. In the present study, the scan rate and cathodic limit (-1000 mV) were kept constant while the range of the anodic scan was altered between 800 and 1400 mV. Extension of the oxidation scan to 1400 mV led to a sevenfold increase in dopamine oxidation current relative to the 'standard' waveform. This was accompanied by a decrease in the dopamine oxidation peak potential. Increased reactant adsorption for both dopamine and DOPAC was the likely cause of enhanced sensitivity. In vivo experiments indicate that, when used with the 1400 mV scan, the carbon fibre electrodes do not poison on contact with brain tissue and can measure dopamine concentrations lower than 50 nM.