Dopamine adsorption at surface modified carbon-fiber electrodes

Fast-scan cyclic voltammetry at high repetition rates was used to characterize adsorptive properties of dopamine (DA) at native and modified carbon-fiber microelectrode surfaces. Disk electrodes were fabricated from Thornel P55 fibers, and cylindrical electrodes, from Thornel T650 fibers. Their surfaces were modified by physisorption of 2,6-anthraquinone disulfonic acid (2,6-AQDS) or chemisorption of 4-carboxyphenyl or catechols. Chemisorption was accomplished via electrochemical reduction of diazonium. salts. The degree of DA adsorption and its oxidation kinetics were found to vary for the two types of native carbon fiber electrodes and with the different chemical overlayers on the carbon surfaces. 2,6-AQDS measurably increased DA adsorption 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 accelerated the DA adsorption rate and sensitivity at P55 disks. However, neither 2,6-AQDS nor 4-carboxyphenyl altered the response at T650 cylinders. Chemisorption of catechols decreased the DA detection sensitivity at both P55 disks and T650 cylinders. The results suggest that electrostatic interactions at the electrode interface are crucial to DA adsorption and detection under these conditions.