Study of self-assembled gold nanoparticle monolayer and multilayer on gold electrode with various generations of pure or ferrocene-tethered PAMAM dendrimer

Abstract

Self-assembled systems with poly (amido-amine) (PAMAM) dendrimers combined with gold nanoparticles have widely studied due to their potential applications in molecular electronics, catalyst carriers, chemical sensors and biomedical devices. Because PAMAM dendrimers have well-defined size, shape and numerous functional sites, many groups have used and studied them to construct nanostructures. First, we synthesized various generations of ferrocene-tethered PAMAM dendrimers. In our work, gold nanoparticle monolayers and multilayers with pure and ferrocene-tethered PAMAM dendrimers as crosslinking molecules were prepared on the mixed self-assembled monolayer (SAM) on gold substrates. The various generations of PAMAM dendrimers can be covalently attached to mercaptoundecanoic acid (MUA) mixed with mercaptoundecanol (MUO) SAM. The gold nanoparticle/dendrimer multilayer films were assembled layer-by-layer via alternated and repetitive exposure of gold nanoparticle and dendrimer solution on gold substrates. Covalently crosslinking with PAMAM dendrimers served as bricks or structure elements to easily build up thin film. Cyclic vlotalmmetry(CV) showed that mixed SAM blocked the electron transfer of $Fe(CN)_6^{3-/4-}$ redox molecule. However, after constructing PAMAM dendrimers on top of the mixed SAM, the faradaic current by $Fe(CN)_6^{3-/4-}$ redox molecules was observed. It means that dendrimers provide the diffusion pathways for the $Fe(CN)_6^{3-/4-}$ redox molecules to reach the gold electrode surface. Moreover, CVs exhibited Au nanoparticle/ Fc-modified PAMAM dendrimer multilayers on Au electrode showing redox peak currents surface coverage increasing as the number of layer is increased. For the gold nanoparticle multilayers with PAMAM dendrimers, cyclic voltammetry(CV), ellipsometry, Fourier transform IR external reflection spectroscopy(FTIR-ERS), and scanning electron microscopy (SEM) revealed that the characteristic values are increased as the number o...