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Binding of p-mercaptobenzoic acid and adenine to gold-coated electroless etched silicon nanowires studied by surface-enhanced Raman scattering

Modern diagnostic tools ever aim to reduce the amount of analyte and the time needed for obtaining the result. Surface-enhanced Raman spectroscopy is a method that could satisfy both of these requirements, provided that for each analyte an adequate substrate is found. Here we demonstrate the ability of gold- sputtered silicon nanowires (SiNW) to bind p- mercaptobenzoic acid in 10-3, 10-4 and 10-5 M and adenine in 30 and 100 μM concentrations. Based on the normal mode analysis, presented here for the first time, the binding of p- mercaptobenzoic acid is deduced. The intensity enhancement of the 1106 cm-1 band is explained by involvement of the C-S stretching deformation, and the appearance of the broad 300 cm-1 band attributed to S-Au stretching mode. Adenine SERS spectra demonstrate the existence of the 7H tautomer since the strongest band observed is at 736 cm-1. The adenine binding is likely to occur in several ways, because the number of observed bands in the 1200 – 1600 cm-1 interval exceeds the number of observed bands in the normal Raman spectrum of the free molecule.

silicon nanowires ; normal mode analysis ; substrate binding, biosensors ; SERS ; mercaptobenzoic acid ; hot spots mapping

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