Estimation of the surface area of a screen-printed carbon electrode modified with gold nanoparticles and cysteine using electrochemical impedance spectroscopy

Abstract

This work concerns with the estimation of the surface area of a screen-printed carbon electrode (SPCE) modified with gold nanoparticles (AuNPs) and cysteine, using electrochemical impedance spectroscopy (EIS). Interpretation of EIS results was based on charge-transfer reactions at high frequencies, followed by diffusion through the monolayers at lower frequencies. Estimates of the electrode fractional surface coverage (θ), active site radius (ra), and the distance between two adjacent sites (2rb) were obtained by assuming that charge transfer occurred at the active sites and that there were planar diffusions of redox species to these sites. Using EIS, fractional surface coverage was estimated to be around 0.467 for EC modified SPCE, 0.497 for ETSC modified SPCE, and 0.25 for ETSTSC modified SPCE. For the EC modified SPCE, the ra and 2rb were estimated to be 14.8 µm and 68 µm. For the ETSC modified SPCE, the estimated ra and 2rb were 14.3 µm and 63.6 µm. The estimated ra and 2rb for ETSTSC were 13.42 µm and 85 µm. respectively. The inactive site areas for EC, ETSC and ETSTSC modified SPCEs were 0.0587 m2, 0.0624 m2, and 0.0314 m2. The results obtained during this research work suggest that modifying SPCEs using gold and cysteine through electrodeposition of AuNPs, linking with thiourea, self-assembly of AuNPs and self-assembly of cysteine (ETSC) resulted in an electrode with sufficiently high surface area that has the potential to be used as a biosensor for skin sensitiser detection.