Waveguide surface plasmon resonance sensing: Electrochemical desorption of alkane thiol monolayers

Combined electrochemical and planar waveguide surface plasmon resonance measurements demonstrating the oxidative desorption through cyclic voltammetry in acid of an alkane thiol monolayer from a gold film are presented in this paper. We show that the thiol film can be systematically removed and we investigate the oxidative mechanism using both a gold wire and evaporated gold on Pyrex surfaces. For the latter we use a combined planar waveguide surface plasmon resonance (SPR) and electrochemical sensor, where the gold pad acts as both the sensing area for SPR measurements and the electrode for electrochemical investigations. The results show a linear relationship between the fractional coverage of the gold electrode and the transmission measured using SPR, and these results are compared to the results of a numerical simulation. This sensing configuration shows promise both for combined electrochemical and optical biosensing and for electrically addressed patterning of biosensor surfaces.