Historical organic dyes : a surface-enhanced Raman spectra (SERS) database on Ag Lee-Meisel colloids aggregated by NaClO4

In the present study, several natural organic dyes used in antiquity, especially in textile dyeing, were analysed by surfaceenhanced Raman scattering (SERS) spectroscopy, in order to build a wide database that could integrate the data previously published in the literature. In particular,we reported for the first time the SERS spectra of 11 dyes: dragon’s blood, sandalwood, annatto, safflower yellow and red, old fustic, gamboge, catechu, kamala, aloe and sap green. Silver colloids (Ag colloids) prepared according to the Lee–Meisel procedure, i.e. by reduction of a silver nitrate (AgNO3) aqueous solution with trisodium citratedihydrate,were used as substrate. As its efficiency had been tested in a previous work, sodium perchlorate (NaClO4) 1.8 M was again employed as aggregating agent, giving the best results when added to the silver nanoparticles after the analyte.