Identification of organic dyes by surface-enhanced Raman scattering in nano-composite agar-gel matrices: evaluation of the enhancement factor

The aim of this work is to improve our understanding of the new possibilities offered by a micro-extraction/surface-enhanced Raman scattering (SERS) identification method for organic dyes used in artworks. Recently, we have shown how it is possible to use a tailor-made extraction process of the dyes present on different kind of substrates by using a nanocomposite hydrogel matrix containing silver nanoparticles, without detriment for the original samples. After minor processing, we identified the extracted dyes thanks to the clear bands in their SERS spectrum, and the comparison with data on reference materials. A usual drawback in SERS/Raman experiments is the lack of information on the sensitivity of the method. Sometimes, quantitative information in SERS is obtained, mostly while working in solution, either with samples of known concentration of the analytes or in presence of an internal standard. Here, in order to obtain similar information on our samples, some specific methods are applied to gain information on the SERS enhancement factor for a reference dye molecule. We report new data on the efficiency of the SERS process for the identification of organic dyes extracted by an agar hydrogel matrix containing silver nanoparticles.