Electrochemical properties of ferrocenylalkane dithiol-gold nanoparticle films prepared by layer-by-layer self-assembly

To explore charge transfer between nanostructured assemblies and an electrode surface, we have performed cyclic voltammetry (CV) of films self-assembled layer-by-layer using gold nanoparticles (NPs) and l-(hexanethiol)-1′-(ethanethiol) ferrocene (FDT). Reflection–Absorption Fourier Transform Infrared Spectroscopy (RAIRS) and Ultraviolet–visible Spectroscopy (UV–vis) of films on aminosilane-functionalised glass slides were used to confirm self-assembly. CV of films on gold electrodes was used to monitor redox peaks of the films following self-assembly of each FDT and NP layer. Addition of a NP layer consistently resulted in a significant decrease in redox peak height, while addition of a subsequent FDT layer resulted in a net overall increase. Occasionally, redox activity dropped substantially but recovered with increasing number of NP–FDT layers. All samples exhibited an increase in redox peak width and a slight increase in peak separation with increasing FDT-linked NP film thickness for the first 4–5 layers. No systematic trend was observed from sample to sample for subsequent layers. These results are consistent with a disordered, porous film structure. Importantly, because of increasing surface area and nanoparticle hopping sites, charge transfer between outer layers and underlying electrodes in such devices is not significantly hampered by increasing number of deposited NP/FDT layers, despite addition of intervening insulating material.