SERS detection of red organic dyes in Ag-agar gel

Micro-Raman spectroscopy has been widely employed in the last few years for the study of artworks, allowing for the characterization of a high class of pictorial materials. However, the detection of organic dyes by conventional Raman spectroscopy is quite difficult, due to the high fluorescence provided by these compounds. Recently, remarkable improvements have been achieved by the introduction of the surface enhanced Raman spectroscopy (SERS) technique for the analysis of organic dyes. In the present work, a new method is presented, based on the use of a SERS probe made of agar-agar coupled with silver nanoparticles, for a non-destructive and minimally invasive micro-extraction of dyes from textiles. Ag-agar gel has been tested first on textile mock-ups dyed with alizarin, purpurin and carminic acid. SERS measurements have been performed adopting laser light excitations at 514.5 and 785 nm of a micro-Raman setup. Highly structured SERS band intensities have been obtained. After having verified the safety of the method by colorimetric, X-ray fluorescence and attenuated total reflectance Fourier transform infrared techniques, a real case, a pre-Columbian piece of textile, have been investigated by Ag-agar gel. This cutting-edge method offers new possibilities for a sensitive and non-destructive analysis of fluorescent materials