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Caitlin Johnson, a master's degree candidate in forensic science at Buffalo State, will present her master thesis seminar, "Assessment of 70 nm Citrate-Capped Gold Nanoparticles (AuNPs) for Surface-Enhanced Raman Scattering (SERS) Substrate Using Rhodamine 6G" at 12:30 p.m. Tuesday, May 3, in Science Building 272. Light refreshments will be served before the seminar. The Chemistry-Physics Seminar Series is supported by the Faculty-Student Association.

Abstract
Raman microscopy is a potentially useful method for detecting drug metabolites in fingerprints and imaging latent fingerprints without a physical or a chemical treatment. However, with normal Raman scattering signals, it is difficult to detect analytes in the mM concentration range, a typical order of the concentration of drug metabolites in sweat. Surface-enhanced Raman scattering (SERS) can improve the intrinsic low sensitivity of normal Raman scattering. The Raman scattering intensity of molecules can be increased by 104–1,010 times when they are adsorbed on a nanoscale metal surface such as gold or silver. For the broader use of SERS in trace chemical analysis, it has long been an important issue to develop a simple and reproducible method to prepare for SERS substrates.

My thesis research has been focused on assessing the SERS activity of citrate-capped gold nanoparticles (AuNPs) having a sphere shape and the diameter of 70 nm. We chose 70 nm AuNPs, because a deposit layer of the AuNPs formed by drop evaporation showed a broad plasmon band above 700 nm wavelengths, which was close to our laser excitation wavelength. The SERS activities of these AuNPs were tested in a deposit layer and a solution using Rhodamine 6G (R6G). Unlike other reports that used smaller size AuNPs,4 the SERS activity of the 70 nm AuNPs showed an inconsistency in the deposit layer. This suggests that the size of AuNPs may play an important role in the formation of a uniform self-assembled monolayer of AuNPs during evaporation and our AuNP layer formed aggregates of AuNPs. On the other hand, we observed a predicted trend of SERS signals in a mixed solution of AuNPs and R6G. The SERS signals of R6G showed a strong dependency on the AuNP concentration, indicating more adsorption sites for R6G molecules was available as the AuNP concentration increased. Using an optimized AuNP concentration, we could detect R6G at the concentration as low as sub-µM concentration.