Dopamine adsorption at surface modified carbon-fiber electrodes

Fast-scan cyclic voltammetry at high repetition rates was used to character ize adsorptive properties of dopamine (DA) at native and modified carbon-fi ber microelectrode surfaces. Disk electrodes were fabricated from Thornel P 55 fibers, and cylindrical electrodes, from Thornel T650 fibers. Their surf aces were modified by physisorption of 2,6-anthraquinone disulfonic acid (2 ,6-AQDS) or chemisorption of 4-carboxyphenyl or catechols. Chemisorption wa s accomplished via electrochemical reduction of diazonium. salts. The degre e of DA adsorption and its oxidation kinetics were found to vary for the tw o types of native carbon fiber electrodes and with the different chemical o verlayers on the carbon surfaces. 2,6-AQDS measurably increased DA adsorpti on and desorption kinetics at P55 disks without a significant change in the measurement sensitivity, the response exhibiting temporal characteristics similar to that for nonadsorbing species. 4-Carboxyphenyl modification acce lerated the DA adsorption rate and sensitivity at P55 disks. However, neith er 2,6-AQDS nor 4-carboxyphenyl altered the response at T650 cylinders. Che misorption of catechols decreased the DA detection sensitivity at both P55 disks and T650 cylinders. The results suggest that electrostatic interactio ns at the electrode interface are crucial to DA adsorption and detection un der these conditions.