Surface-Enhanced Raman Spectroscopy of Acetil-neuraminic Acid on Silver Nanoparticles: Role of the Passivating Agent on the Adsorption Efficiency and Amplification of the Raman Signal

Abstract

We present a combined experimental and theoretical study dedicated to analyzing the surface-enhanced Raman spectra of solutions of citrate-covered silver nanoparticles (NPs) in the presence of acetil-neuraminic acid (Neu5Ac). The Raman signals from Neu5Ac (particularly the bands located at 1002 and 1237 cm–1) can easily be detected for concentrations as low as 1 mg/dl, providing outstanding molecular sensing properties for our synthesized Ag-NPs. When compared to its solid phase, Neu5Ac adsorption on citrate-covered Ag particles leads to enhanced Raman intensities; many vibrational frequencies are shifted; and relative intensities undergo significant changes. These variations in the spectra complicate molecular identification, especially in mixed overlayers as the ones considered in this work. Consequently, experimental results are discussed on the basis of extensive density functional theory (DFT) calculations on model citrate-covered silver clusters with coadsorbed Neu5Ac species. Several citrate–Neu5Ac...