Dynamic Raman Scattering Studies of Coated Gold Nanoparticles: 4-Mercaptopyridine, 4-Mercaptophenol, and Benzenethiol

摘要

We have demonstrated several benefits of dynamic Raman scattering (DRS) measurements on coated gold nanoparticles. DRS examines particles moving in and out of a focused laser beam and uses statistical methods to, determine unusual particles signals from the average particle response. In order to illustrate chemical enhancements within inaccessible particle gaps, we examined the pH dependence of 4-mercaptophenol, 4-mercaptopyridine, and benzenethiol. This study develops the methods of correlograms to visually display large data sets in a meaningful way to show trends in distributions and correlation between Raman features within a Set of particles. Our correlograms demonstrate the correlations between Raman peaks within large data sets and illustrate which peaks may be involved in local-chemical environments within a hotspot. The correlograms also provide clear proof of rare but stronger enhancing outlier particles. Principal component analysis (PCA) was used to extract the unusual particle signals from the average such that pH depended chemical effects could be determined. Both 4-mercaptopyrdine and 4-mercaptophenol exhibited, pH dependence when examined by DRS. The variance between signals of the unusual: events to the average was used to determine a rough estimate of the unusual particle enhancement as 150.