High Sensitive Analysis Using Surface Enhanced Raman Scattering with Self-assembled Gold Nanoparticles

Abstract

Self-assembled gold nanoparticles (AuNPs) are attractive issue of combination of nano structure and localized plasmon resonance (LPR) including surface enhanced Raman scattering (SERS). Anisotropic aggregation of AuNPs are typical nanostructure which are spontaneously made in colloidal dispersion and show unique SERS activity. Colloidal AuNPs are, however, intrinsically so un stable that these LPR correspond to the morphology of the aggregation are easily lost. We have achieved the stable and controllable self-assembling procedures of AuNPs by termination with charged planar nanoparticles. At the early stage of the self-assembling under diffusion limited condition, relatively simple anisotropic assembles of AuNPs of with fractal dimension of 1.4 was produced. These colloidal assembles show LPR wavelength at about 785 nm, therefore these assembles are appropriate for 785 nm SERS. More complicated aggregation is given with higher fractal dimensions following the simple anisotropic assembles. After mixing the dispersion of these AuNPs with 4,4’-bipyridine aqueous solution, SERS signal of 50 nM sample were immediately observed. The longevity in SERS activity of the pre-aggregated AuNPs dispersion was confirmed over months even in aqueous media without any surfactant or hydrophilic polymer. We also applied these assembles to label-free, quantitative and selective measurements of aqueous solution of biomolecules.