Surface-enhanced Raman scattering (SERS) study of anthocyanidins

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

“…Common features can be found at ~1190 cm −1 , whose presence can be attributable to a contribution of CYN 3‐glucoside, and at ~1250, 1320–1330 and 1630 cm −1 . While the latter two signals could be related to ring stretching vibrational modes, the bands at 1630 cm −1 present also a contribution from the CO stretching of anthocyanins in their blue quinoidal form, predominant at this pH value with respect to the red one . Moreover, two signals at ~1500 and 1530 cm −1 are present in all the spectra, with the exception of purple corn that exhibits only the signal at 1504 cm −1 .…”

“…In this case, however, the spectral patterns show a better correspondence with the SER spectrum of the aglycone CYN than to that of CYN 3‐glucoside, which is instead recognizable in the spectra obtained from the plant sources (Figs and ). Such hypothesis is formulated mainly looking at the SER spectra obtained at acidic pH, the condition at which the glucoside and its aglycone show remarkably different spectral patterns, as previously demonstrated . In more detail, at this pH value, the extracts from dyed textiles mainly containing CYN show signals at ~1240 and 1330 cm −1 , the strongest signal at ~1530 cm −1 and ultimately a band at ~1590 cm −1 .…”

“…In more detail, at pH 4, they show a characteristic spectral pattern with strongest signals at ~1240, 1330, 1530, 1590 and 1640 cm −1 . All these bands were attributed to ring stretching vibrational modes, with the exception of the signals at ~1240 cm −1 that are related to the stretching of C–OH bond . Their patterns can be related to those of CYN and its 3‐glucoside, even if some differences in the exact wavenumbers of the signals could contribute to the differentiation of the spectra.…”

“…SERS effect is based on the relevant enhancement of the Raman signals of a given molecule, which takes place when the molecule is in the proximity of, or even adsorbed on, a metal surface with nanometric roughness. Recently, the authors characterized the six most common anthocyanidins by means of SERS . In the present work, methods for the identification of anthocyanins from both plant sources and dyed wool are developed.…”

Surface-Enhanced Raman Spectroscopy: Using Nanoparticles to Detect Trace Amounts of Colorants in Works of Art

“…The molecule of interest, alizarin, is adsorbed onto an Ag nanoparticle substrate. The substrate is then irradiated with laser light (green), and the enhanced Raman scattering (red) is detected Geiman et al 2009;Chang et al 2009;Xie et al 2012;Bruni et al 2011a;Mayhew et al 2013;Benedetti et al 2014;Greeneltch et al 2012;Doherty et al 2014;Cañamares and Lombardi 2015;Zaffino et al 2015) can also be found in the literature. In addition to providing valuable reference spectra for identification purposes, these works have explored aspects such as the influence of pH on the resulting spectral patterns, and the binding geometry and relative orientation of the molecules examined with respect to the metal surface.…”