Electroanalytical applications of cationic self-assembled monolayers, square-wave voltammetric determination of dopamine and ascorbate

Gold electrodes modified with cationic self-assembled monolayers (SAMs) of 2,2 ' -dithiobisethaneamine (CYST) and 6,6 ' -dithiobishexaneamine (DTH) we re used for the simultaneous determination of dopamine (DA) and ascorbate ( Ah). The cationic SAM modified electrodes have several advantages over the bare electrode for the oxidation of AA. A very large(similar to 450 mV) dec rease in the overpotential for the oxidation of AA when compared with the b are electrode has been observed at the cationic monolayer-modified electrod e. The electrostatic interaction of negatively charged AA with the monolaye r shift the oxidation peak potential of AA to less positive potential and e nhances the peak current. On the other hand, the positively charged DA is r epelled from the monolayer and the oxidation potential shifts to more posit ive potential when compared to the bare electrode. The electrochemical oxid ation of AA at the mixed monolayer of CYST and diethyl disulfide (DEDS) sup ports the influence of cationic terminal group of the monolayer on the oxid ation of AA. Since the oxidation of AA occurs well before the oxidation pot ential of DA is reached, the homogeneous catalytic oxidation of AA by the o xidized DA has been advantageously eliminated at the monolayer-modified ele ctrode. The cationic self-assembled monolayers successfully detect DA in th e presence of high concentration of AA. The sensitivity of the electrode mo dified with CYST monolayer was found to be 0.036 and 0.021 muA/muM towards AA and DA, respectively. (C) 2001 Elsevier Science B.V. All rights reserved .