Historical organic dyes: a surface-enhanced Raman scattering (SERS) spectral 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 surface‐enhanced 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 citrate dihydrate, 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. Copyright © 2011 John Wiley & Sons, Ltd. In the present study, a surface‐enhanced Raman spectral (SERS) database of natural organic dyes used in antiquity in textile dyeing was built, using Ag Lee–Meisel colloids as a substrate and NaClO4 1.8 M as aggregating agent, giving the best results when added to the nanoparticles after the analyte. In particular, we report for the first time the SERS spectra of dragon's blood, sandalwood, annatto, safflower yellow and red, old fustic, gamboge, catechu, kamala, aloe and sap green. The spectral patterns of such colorants are thus discussed in relation to those of other dyes belonging to the same molecular class.