Direct modulation of localized surface plasmon coupling of Au nanoparticles on solid substrates via weak polyelectrolyte-mediated layer-by-layer self assembly.

For the first time, a pH-controllable weak polyelectrolyte/metal nanoparticle composite film was successfully constructed on a solid substrate through layer-by-layer (LbL) assembly, and its localized surface plasmon coupling (LSPC) was investigated. The degree of LSPC can be modulated by controlling pH of the weak polyelectrolyte used. The LSPC was tunable and stable, demonstrated by a large shift of the longitudinal band peak position over a range of 625-741.5 nm as a function of pH, while shifting insignificantly at a fixed pH for a month. The modulation of LSPC of the LbL nanocomposite film can be ascribed to changes in the assembled weak polyelectrolyte, where the charge density and conformation can be easily controlled by pH to tailor the interparticle spacing in the nanoparticle clusters. This work provides a rational approach for preparation of stable nanocomposites with easily tunable LSPC and scientific insight into the effect of film morphology on the optical properties of assembled nanoparticles. The spectral response to the environment has great potential in applications such as plasmonics, biosensing, and medical therapy.