| Abstract
| - Polymeric molecules containing multiple thiol groups (polythiols) provide tenacious attachment to metalsurfaces such as gold. Polythiol films are also well suited for subsequent derivatization with biomacromolecules through remnant free thiol groups of the film. In this study, 1−3 nm thick layers of a commercialpolythiol, poly((mercaptopropyl)methylsiloxane) (PMPMS), are investigated with X-ray photoelectronspectroscopy (XPS) and electrochemical impedance spectroscopy. XPS is used to reveal the surface coverageof thiolate−Au bonds between the polythiol and the metal support, which is found to be approximately30% lower than that in alkanethiol self-assembled monolayers. The surface density of thiolate−Au bondsdid not depend on film thickness provided sufficient PMPMS material was present. Differential capacitancemeasurements show that the effective dielectric barrier presented by PMPMS films under aqueousenvironments corresponds closely to their physical thickness, with even ∼1 nm films remaining impermeableto electrolyte species. Modification of the films with an oligoethylene glycol compound was also examined,in anticipation of future applications in label-free, impedance-based biomolecular diagnostics.
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