Investigation of the interactions between ligand-stabilized gold nanoparticles and polyelectrolyte multilayer films

We examine the interactions between gold nanoparticles stabilized by the 4-(dimethylamino)pyridine (DMAP-AU(NP)) and various polyelectrolytes (PEs), both in solution and in layer-by-layer (LbL) assembled multilayer films. UV-vis spectrophotometry studies showed that the plasmon absorption band of the DMAP-Au-NP in solution red-shifts and broadens in the presence of poly(sodium 4-styrenesulfonate) (PSS), poly(allylamine hydrochloride) (PAH), or poly(ethyleneimine) (PEI). This suggests that the polyanion PSS electrostatically associates with the nanoparticles, while PAH and PEI bond through the amine functionalities, despite having the same charge as the nanoparticles. In contrast, the addition of poly(diallyldimethylammonium chloride) (PDADMAC) to a DMAP-Au-NP dispersion has no influence on either the peak position or shape of the absorption spectrum of the nanoparticles, indicating no interaction. PE/nanoparticle hybrid films were assembled by a single-step adsorption of the DMAPAu(NP) into preassembled LbL PE multilayer films. The interactions between the DMAP-AU(NP) and the multilayer films were investigated by UV-vis spectrophotometry, quartz crystal microgravimetry, and surface plasmon resonance spectroscopy. These experiments revealed that PAH/PSS films have a highly uniform and dense DMAP-Au-NP coverage, which is attributed to the bonds formed between the nanoparticles and PAH and PSS in the films. Additionally, the DMAP-Au-NP adsorbed amount and the nanoparticle-nanoparticle interactions (and hence film optical properties) can be controlled by the number of preassembled PAH/PSS bilayers. In contrast, for PDADMAC/PSS films only a sparse and nonuniform DMAP-Au-NP coating is obtained, and an irregular trend between PE bilayer number and DMAP-Au-NP adsorbed amount was observed. The results obtained indicate that the combined interactions originating from PAH and PSS with DMAP-Au-NP facilitate the preparation of stable nanoparticle/PE thin films with tailored optical properties. Such films may be exploited in diverse areas, including electrochemical sensing, colloidal crystals, and controlled delivery.