Surface Enhanced Raman Spectrometry on Silver Hydrosols Studied by Flow Injection Analysis

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Abstract
Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm−1 with an Ar+ laser at 514.5 nm.