The effect of silver oxidation on surface-enhanced Raman scattering (SERS) was investigated using citrate-reduced silver nanoparticles (Ag NPs) (45-50 nm in diameter) immobilized on glass substrate. Oxidation of Ag NPs was performed in controlled ozone environment under UV irradiation. The extent of oxidation was characterized by X-ray photoelectron spectroscopy (XPS). The SERS activity of pristine and oxidized Ag NPs was assessed using trans-1,2-bis(4-pyridyl)ethylene (BPE) and sodium thiocynate as model analytes at the excitation wavelength of 532 nm. The exposure of Ag NPs to ppm-level concentrations of ozone led to the formation of Ag2O and orders of magnitude reduction in SERS enhancement factor (EF) for BPE and NaSCN. Such adverse effect was also notable upon exposure of Ag NPs under ambient condition where ozone exists at ppb-level. The correlated XPS and SERS studies suggest that formation of just a sub-monolayer Ag2O is sufficient to decrease markedly the SERS EF of Ag NPs. UV irradiation and ozone have a synergistic effect on silver oxidation and thus its detrimental effect on SERS enhancement of Ag NPs.
Citation: Journal of Analytical Chemistry
Pub Type: Journals
Raman, surface enhanced, SERS, XPS, nanoparticles, detection