We report a novel one-pot method for the synthesis of monodisperse colloidal gold nanorings (Au NRs). Au NRs were obtained via galvanic replacement of sacrificial Co nanoparticles (Co NPs) with gold in the presence of low molecular weight poly(vinylpyrrolidone) (PVP, Mw = 2,500) as a stabilizing agent. The outer and inner diameters of Au NRs were controlled by the size of Co NPs and the concentration of gold salt, leading to tunable surface plasmon resonance (SPR) from visible to near infra-red range. Numerical simulation using finite different time domain (FDTD) approach was used to calculate the electric field distribution around individual as well as clustered Au NRs. The field was found to be most intense in the center for discrete Au NRs and yet the strongest at the joints clusters form, commonly referred to as hot spot. Au NRs immobilized on quartz slice substrates at various coverage densities were utilized for surface-enhanced Raman scattering (SERS) measurements using trans-1,2-bis(4-pyridyl)ethylene (BPE) and Rhodamine 6G (R6G) as model analytes. The Raman intensity of BPE was shown to increase linearly with the coverage density of Au NRs when discretely distributed but exponentially when clustered. In contrast, the Raman intensity of R6G exhibited a linear correlation with the coverage density with or without cluster formation. The results will be interpreted based on the different adsorption behavior of the two analyte molecules on Au NRs especially when clusters are formed.

One-pot synthesis and plasmonic characteristics of colloidal gold nanorings

247th National Meeting (2014)

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