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 was found that, in some cases, the spectral contribution of the second colorant in the mixture goes undetected unless it is present in significant concentrations. Results of this work provide an indication of the expected performances of SERS in the analysis of dye mixtures. The findings also highlight the need for further research in the area of combined separation and quantification with SERS detection of organic colorants in artworks and museum objects.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films