Specific behavior of the p-aminothiophenol – Silver sol system in their Ultra-Violet–Visible (UV–Visible) and Surface Enhanced Raman (SERS) spectra

• Aliphatic aminothiol can induce the aggregation of citrate stabilized silver sol.
• The p-aminothiophenol induced aggregation of Ag colloid has electrostatic nature.
• In diluted aqueous solutions, p-aminothiophenol (p-ATP) oxidizes depending on the pH.
• Oxidized form of p-ATP is necessary for “b2-mode enhancement” in the SERS spectrum.
• Azo-bridge formation seems to be responsible for the “b2-mode enhancement.”

The UV–Visible and Surface Enhanced Raman Spectroscopy (SERS) behavior of silver sol (a typical SERS agent) were studied in the presence of different bifunctional thiols such as p-aminothiophenol, p-mercaptobenzoic acid, p-nitrothiophenol, p-aminothiophenol hydrochloride, and 2-mercaptoethylamine hydrochloride in diluted aqueous solution. Our results confirm that the p-aminothiophenol induced aggregation of citrate stabilized silver colloid originates from its electrostatic nature, as well as the azo-bridge formation cannot be the reason of the observed time dependent UV–Visible spectra. Based on our parallel SERS and electrospray ionization mass spectrometry measurements, we have concluded that certain amount of oxidized form of the probe molecule has to be present for the so-called b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Our findings seem to support the idea that the azo-bridge formation is responsible for the b2-mode enhancement in the SERS spectrum of p-aminothiophenol.

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