Electron Transfer Across an Antifouling Mercapto-hepta(ethylene glycol) Self-Assembled Monolayer

Abstract

Oligo(ethylene glycol) films are known to be very efficient at reducing the nonspecific adsorption of biomacromolecules on surfaces, but they often show a tendency to decrease drastically the rate of heterogeneous electron transfer at the modified surface, making them unsuitable for electrochemical biosensing. In this work, the heterogeneous electron transfer across the self-assembled monolayer of a short thiolated oligo(ethylene glycol) is investigated using four redox systems: [Fe(CN)6]3–/4–, [Ru(NH3)6]3+/2+, Fc(MeOH)2+/0, and [IrCl6]2–/3–. Fast electron-transfer kinetics are evidenced in all cases except the ferri/ferrocyanide couple, for which the electron transfer is completely suppressed. Interfacial characterizations by means of spectroscopic ellipsometry, electrochemical desorption experiments, and capacity measurements indicate that the film consists of a fairly hydrated single monolayer with a surface concentration of 4.1 × 10–10 mol cm–2. The peculiar behavior of [Fe(CN)6]3–/4– is discussed in ...