Dispersion Stability, Ligand Structure and Conformation, and SERS Activities of 1-Alkanethiol Functionalized Gold and Silver Nanoparticles

Dispersion stability, ligand structure and conformation, and SERS activities of 1-alkanethiol (CnH2n+1SH, n = 214) functionalized gold and silver nanoparticles (AuNPs and AgNPs) were studied as a function of alkanethiol carbon chain length and nanoparticle (NP) type and size. The dispersion stability of alkanethiol functionalized NPs in water increases with increasing alkanethiol chain length and NP size, and the stabilities of the alkanethiol-containing AuNPs are higher than their AgNP counterparts. C3H7SH and longer alkanethiols are highly ordered on AgNPs but disordered on AuNPs. The SERS intensity of the CS stretch band for the model alkanethiols on AgNPs and AuNPs decays exponentially (I = I-0 exp(-N-c/N-0)) with increasing number of carbon atoms (N-c). The empirical decay length N0, in terms of the number of the carbon atoms, is 1.29, 0.53, and 0.10 for AgNPs with diameters of 50, 30, and 10 nm, respectively. This decay length is less than 1 for AuNPs of difference sizes. These results show that changing the NP gap size by a distance equivalent to a single chemical bond can have a significant impact on the NP integrated SERS activities.