Subsecond adsorption and desorption of dopamine at carbon-fiber microelectrodes

High-repetition fast-scan cyclic voltammetry and chronoamperometry were use d to quantify and characterize the kinetics of dopamine and dopamine-o-quin one adsorption and desorption at carbon-fiber microelectrodes, A now inject ion analysis system was used for the precise introduction and removal of a bolus of electroactive substance on a sub-second time scale to the disk-sha ped surface of a microelectrode that was fabricated from a single carbon fi ber (Thornel type T650 or P55), Pretreatment of the electrode surfaces cons isted of soaking them in purified isopropyl alcohol for a minimum of 10 min , which resulted in S/N increasing by 200-400% for dopamine above that for those that were soaked in reagent grade solvent. Because of adsorption, hig h scan rates (2000 V/s) are shown to exhibit equivalent S/N ratios as compa red to slower, more traditional scan rates. In addition, the steady-state r esponse to a concentration bolus is shown to occur more rapidly when cyclic voltammetric scans are repeated at short intervals (4 ms). The new methodo logies allow for more accurate determinations of the kinetics of neurotrans mitter release events (10-500 ms) in biological systems. Brain slice and in vivo experiments using T650 cylinder microelectrodes show that voltammetri cally measured uptake kinetics in the caudate are faster using 2000 V/s and 240 Hz measurements, as compared to 300 V/s and 10 Hz.