Localized surface plasmon resonance coupling in Au nanoparticles/phosphorus dendrimer multilayer thin films fabricated by layer-by-layer self-assembly method

Multilayer thin films of anionic gold nanoparticles (Au_NPs) and cationic phosphorus dendrimers were deposited on 3-(diethoxymethyl-silyl) propylamine (3-APDMES)-coated substrates using layer-by-layer (LbL) assembly driven by electrostatic interactions. The growth of Au/dendrimer multilayers composed of Au_NPs with diameters of ∼3 nm and ∼16 nm and dendrimer with ∼2 nm diameter was monitored by UV-vis spectroscopy. The relative amounts of Au_NPs and dendrimers in the multilayer films were calculated using a quartz crystal microbalance. The Au-containing multilayers have two surface plasmon bands at ∼530 nm and ∼600 nm, where the latter exhibits a red shift upon increasing the areal density of AuNPs as well as increasing the layer number. The localized surface plasmon resonance (LSPR) band of the hybrid films can be tuned by adding NaCl to the dendrimer solution or by removing the organic matrix. These results demonstrate that the near-field coupling between the LSPR bands of neighboring Au layers is responsible for the controlled absorption behavior. Au mesoporous films after removing dendrimers show LSPR sensing properties for alcohols with different refractive indices in the range 1.33-1.41. A linear relationship was obtained between the LSPR peak wavelength and the refractive index of the surrounding medium.