Closely Adjacent Ag Nanoparticles Formed by Cationic Dyes in Solution Generating Enormous SERS Enhancement

Abstract

Explicit evidence is reported to prove that huge surface enhanced Raman scattering (SERS) signal from cationic dye results from its adsorption at the nanogap of neighboring Ag particles. The addition of extremely small amount of cationic dye such as 10−8 M R6G+ provokes the formation of closely adjacent Ag nanoparticles in aqueous solutions exploiting electrostatic forces, of which surface residue was substituted by Cl− anions (10 mM) in advance to have negative charges. This is ensured by the appearance of a coupled localized surface plasmon (LSP) peak at 600−700 nm in addition to that for isolated particles at about 400 nm. The adjacent state of the Ag nanoparticles, which does not render coagulated precipitates but flocculates, suspended particles, is quite stable for more than 24 h as confirmed by invariable extinction spectra. Simultaneously, the linked Ag nanoparticles confer enormous SERS signal and prominent red-shifted fluorescence of the dye molecules. Consequently, markedly enhanced electric fi...