Determination of dopamine in the presence of high concentration of ascorbic acid by using gold cysteamine self-assembled monolayers as a nanosensor

A monolayers of cysteamine (CA) was prepared on a polycrystalline gold electrode through self-assembly procedure to produce a gold cysteamine self-assembled monolayers (Au-CA SAMs) modified electrode. Characterization of the modified electrode was performed by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was used to evaluate pKa of the adsorbed CA on the gold surface, and a value of 7.6 was obtained for the Au-CA surface pKa. The charged terminal groups of monolayers served for determination of dopamine (DA) in the presence of high concentration of ascorbic acid (AA) using differential pulse voltammetry (DPV). Well-separated DA and AA voltammetric waves (∼330 mV) were observed at the Au-CA SAMs electrodes in an acidic solution. A calibration curve with two linear parts was obtained for DA, 6.00 × 10−6 to 3.84 × 10−4 M and 3.36 × 10−4 to 9.50 × 10−3 M, with correlation coefficients 0.997 and 0.992, respectively. The detection limit for DA was found to be 2.31 μM in the presence of 1.0 mM AA. The apparent charge transfer rate constants (kapp) of AA and DA were evaluated by using EIS measurements on the modified electrode as 44.0 cm s−1 × 10−8 cm s−1 and 2.45 cm s−1 × 10−8 cm s−1, respectively.