SERS Discrimination of Closely Related Molecules: A Systematic Study of Natural Red Dyes in Binary Mixtures

Abstract

Recent methodological and instrumental advances have afforded surface-enhanced Raman spectroscopy (SERS) wide recognition in the cultural heritage field as a powerful tool for the analysis of organic colorants. The many advantages of SERS are counterbalanced by the fact that it has limited ability to resolve dye mixtures. In this work, a systematic study was conducted to determine the technique’s ability to discriminate closely related molecules in binary mixtures for a selection of natural red dyes widely used in painting and textile dyeing (alizarin, purpurin, carminic and laccaic acids, brazilein). Spectra were recorded on two different metal substrates, i.e., citrate-reduced silver colloids and silver films over nanospheres (AgFONs). After working on reference systems, the study was expanded to include analysis of red lake oil paint reconstructions upon hydrolysis with hydrofluoric acid, aiming to gain a deeper understanding of how varying the experimental conditions may affect dye identification. It ...