Identification of anthocyanins in plant sources and textiles by surface-enhanced Raman spectroscopy (SERS)

Abstract

The aim of the present study was to provide experimental procedures for the identification of anthocyanin‐based dyes used in antiquity. In particular, we assessed the possibility to identify anthocyanins, both in plant extracts and in dyed textiles, by means of surface‐enhanced Raman spectroscopy (SERS), a very chemically specific technique that is moreover sensitive to the changes in structures of molecules, phenomena that occur extensively in the chemistry of anthocyanins. The choice of the plant sources (bilberry, elderberry, sumac, purple corn and hollyhock) was based on their attested use in history as dyeing matters. Suitable extraction and pre‐treatment procedures were optimized both for plant sources (berries, cob glumes and flowers) and textiles dyed with such sources in the laboratory, followed by SERS analyses at different pH values. Finally, special attention was paid to the well‐known instability of anthocyanins: dyed wool samples were exposed to artificial aging in order to verify the possibility to identify such molecules also in faded textiles. The achievement of reliable surface‐enhanced Raman spectra from these samples encourages us to suggest the protocol for the analysis of historical objects. Copyright © 2015 John Wiley & Sons, Ltd.

On the identification of folium by SERS: from crude extracts to illuminated codices

“…Also, it is noteworthy that the SER spectra of both blue and purple extracts differ significantly from those reported by Zaffino et al . in their characterization of anthocyanins from plant sources.…”

“…Also, it is noteworthy that the SER spectra of both blue and purple extracts differ significantly from those reported by Zaffino et al [36] in their characterization of anthocyanins from plant sources. In the past, some authors hypothesized that the main constituents of folium could be anthocyanins, [37] but our results compared with those of Zaffino et al seem to exclude this hypothesis.…”

“…As the dye is not an excellent SER probe, only a few signals are normally detected, although richer spectra can also appear sporadically if many analytical spots are considered. The comparison of the obtained SER spectra here with those obtained from other natural colorants that can produce purple hues such as cochineal, [39] brazilwood, [39] plants bearing anthocyanins, [36] alkanet (unpublished data) and purple dyes from lichens [13] excludes any structural similarity with the dyes from C. tinctoria. The structure of the dyeextracted Chrozophora is therefore still to be clarified, and presently, we cannot rely on an accurate spectroscopic interpretation of the SER signals to guide the assignment.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…This same author and co‐workers reported the use of online coupling of HPLC with SERS for the identification of historical dyes. Examples were presented of some of the colourants most widely used in history, such as morin and luteolin for yellow dyes, alizarin, purpurin, laccaic, kermesic, and carminic acids for red ones, and indigotin for blue tints . Zhou et al reported using Raman and SERS on horns and their correlation with biomechanical properties.…”

“…Examples were presented of some of the colourants most widely used in history, such as morin and luteolin for yellow dyes, alizarin, purpurin, laccaic, kermesic, and carminic acids for red ones, and indigotin for blue tints. [46] Zhou et al reported using Raman and SERS on horns and their correlation with biomechanical properties. SERS measurements verified that the main constituents of the degradation products from both buffalo and sheep horns were amino acids and polypeptides, suggesting that these horns are suitable candidates for biomaterial scaffolds.…”