Size correlation of optical and spectroscopic properties for gold nanoparticles

While the optical and spectroscopic properties of gold nanoparticles are widely used for chemical, bioanalytical, and biomedical applications, the study of the size correlation with these properties for nanoparticles in solutions is rather limited. This paper describes the results of a systematic study of such a correlation for gold nanoparticles with diameters ranging from 10 to 100 nm in aqueous solutions. The high monodispersity of these nanoparticles permitted a meaningful correlation of the particle size with the surface plasmon (SP) resonance band properties and the surface-enhanced Raman scattering (SERS) spectroscopic properties. This correlation is compared to the results from the simulation based on Mie theory. The close agreement between the experimental and the theoretical results provides insight into the validity of determining the wavelength of the SP resonance band as a measure of the particle size. The size correlation with the SERS intensity from the adsorption of 4-mercaptobenzoic acid on the nanoparticles in aqueous solutions reveals the existence of a critical size of the nanoparticles in the solution beyond which the particle-particle interaction is operative and responsible for the SERS effect. These findings serve as the basis of size correlations for exploiting the optical and spectroscopic properties of gold nanoparticles of different sizes in aqueous solutions in analytical or bioanalytical applications.