Electrochemical and Morphological Characterization of New Architectures Containing Self-Assembled Monolayers and Au-NPs

Abstract

Pure 1,10-decanedithiol (C10-SH) and mixed (1-decanethiol:1,10-decanedithiol) self-assembled monolayers (SAMs) prepared from ethanolic solution on Au(111) surfaces have been used in order to investigate the effect of the SAM organization and the availability of free −SH groups at the SAM/solution interface on the development of layer-by-layer architectures containing SAMs and gold nanoparticles (Au-NPs). The SAM modified electrodes have been electrochemically characterized by cyclic voltammetry in alkaline medium (reductive desorption) and in the presence of an electroactive species, Fe(CN)63−, in KNO3 solution, enabling the evaluation of the stability and organization of the SAMs. Enhanced stability, organization, and hindrance to the electron transfer were found for the mixed SAMs with increasing thiol content, when compared with the pure dithiol SAM. The mixed SAM prepared from solution containing the thiol to dithiol proportion of (50:1) and pure C10-SH SAMs have been selected for further modification; the electrochemical quartz crystal microbalance (EQCM) enables the detection of different amount of citrate stabilized Au-NPs attachment to the selected SAMs modified electrodes due to distinct availability of free −SH groups at the SAM/solution interface and the electrochemical characterization of the layer-by-layer assemblies (based on pure C10-SH and mixed SAMs) showed that the electron transfer (ET) properties of the such architectures strongly depend on the nature of the base SAM and amount of immobilized Au-NPs. Atomic force microscopy (AFM) morphological characterization of the C10-SH SAM upon layer-by-layer modification was performed ex situ in air.