Self-assembled monolayers of 6-mercapto-1-hexanol and mercapto-n-hexyl-poly(dT)18-fluorescein on polycrystalline gold surfaces: An electrochemical impedance spectroscopy study

The following study presents the analysis of electrochemically induced conformational changes of self-assembled single-stranded DNA (mercapto-n-hexyl-poly(dT)18-fluorescein, 18TFAM) on polished polycrystalline Au electrodes. This was compared to a self-assembled monolayer of 6-mercapto-1-hexanol (MCH). Double layer capacitance (Cdl) was determined by electrochemical impedance spectroscopy (EIS) with electrochemical perturbation from 0.0 V to 0.7 V (vs. Ag/AgCl) for bare Au, Au/mercaptohexanol (Au/MCH), and Au/S-(CH2)6-poly(dT)18-fluorescein (Au/18TFAM) self-assembled monolayers. The EIS study was done with two electrolyte systems, KH2PO4 and NH4H2PO4 solutions at pH 9.9 and 10.05, respectively. The results were used to determine the ion barrier factor for MCH and 18TFAM for each phosphate solution. Moreover, detailed experimental analysis carried out by repetitively switching the electrochemical potential between 0.2 and 0.5 V (vs. Ag/AgCl) strongly suggests the stretching/condensing of the specifically attached 18TFAM on the Au surface and the progressive desorption of non-specifically adsorbed 18TFAM.