In this work we describe the electrostatic LbL assembling of negatively charged gold nanoparticles (NP6: 6.4±0.6 nm and NP11: 11.0±0.7 nm) with a viologen-based cationic redox polyelectrolyte (PV) on quartz slides negatively charged by activation in basic medium or gold electrodes modified by 3-mercapto-1-propane-sulfonic acid. The growing of PV-NP assemblies was demonstrated from UV-visible experiments showing an increase of the NP6 or NP11 surface plasmon resonance absorption band intensity as a function of the number of layers. Red shifting of the maximum corresponding to the surface plasmon resonance band as compared with the absorption spectrum of the NP colloidal gold is obtained for either increasing adsorption times or number of layers. Results for increasing adsorption times are explained using an effective medium theory which takes into account that gold nanoparticles are embedded in a host matrix and, consequently, subject to an average polarization field due to both the matrix and the surrounding particles. On the other hand, red shifting with number of layers is explained in terms of electromagnetic coupling of gold nanoparticles in the different layers.
In addition, in situ ellipsometric studies were performed to follow the step-by-step growth of the PV-NP assemblies on MPS-thiolated gold surfaces. The y - Ä trajectories obtained at different wavelengths (546.1 and 632.8 nm) for assemblies ended either in PV or NP using different NP time adsorption (15 or 60 minutes), were fitted based on a single layer model with uniaxial optical anisotropy. Optical properties as well as thickness for the different LbL assemblies were obtained.
