Gold nanoparticles (NPs) were prepared by reduction with salicylic acid in aqueous solution. The resulting dispersions were found to contain a mixture of flat triangular/hexagonal and smaller close-to-spherical NPs. As expected from theoretical considerations, such nanocolloids display two clearly differentiated surface plasmon bands at 540 and 860 nm associated with spherical and anisotropic triangular/hexagonal NPs, respectively. Layer-by-layer (LBL) assembly was used to deposit thin films of the Au colloids. UV−visible data indicate preferential adsorption of the flat particles on polyelectrolyte films. Importantly, a new band developed at 650 nm as the number of the Au NPs bilayers increased. This finding indicates that there exists a strong interaction between the NPs in adjacent layers, resulting in the surface plasmon absorption at a new wavelength. The insertion of extra polyelectrolyte or montmorillonite layers between the Au bilayers was shown to gradually reduce the interlayer interaction and r...