Characterization of the Reductive Desorption of Self-Assembled Monolayers on Platinum Surfaces

Abstract

Thiol-based self-assembled monolayers (SAMs) have been widely characterized on gold surfaces, with the desorption potentials of these SAMs being of special interest for nanotechnology and biological applications. However, the study and determination of desorption potentials of thiol SAMs on platinum surfaces has been limited by the hydrogen evolution reaction (HER) catalyzed by the metal, which dominates response signals when studying the system through conventional electrochemical techniques.Through the coupling of electrochemical techniques with fluorescence microscopy, the problem of the HER signal can be avoided in the study of desorption potentials for the platinum-thiol monolayer systems. By using fluorescent thiols, as well as monocrystalline platinum spheres, the desorption potential for different crystallographic orientations and thiol length combinations can be determined. The results obtained show that the desorption of Bodipy C10SH thiols from platinum surfaces occur at more positive potentials in [111] crystallographic orientations, and at more negative potentials at [100] ones. On the other hand, no notable difference was found in the desorption order of Bodipy C16SH from these two orientations.However, the use of fluorescence microscopy for the solution of this problem poses other challenges: the time the thiols need to separate enough from the metallic substrate to not be affected by quenching, as well as the facts that thiols fluoresce less as they dilute and the existing spectral overlap for the molecules, adds difficulties to the establishment of the desorption potentials.Through COMSOL Multiphysics simulations, we try to simulate the systems hereby proposed of platinum with thiol-based SAMs. Using them, the desorption potentials, as well as the monolayer coverage under specific conditions, can be determined. We expect that, with further development of the model, more specific values for these variables can be determined. Figure 1