SERS detection of red organic dyes in Ag‐agar gel

Abstract

Micro-Raman spectroscopy has been widely employed in the last few years for the study of artworks, allowing for the characterization of a high class of pictorial materials. However, the detection of organic dyes by conventional Raman spectroscopy is quite difficult, due to the high fluorescence provided by these compounds. Recently, remarkable improvements have been achieved by the introduction of the surface enhanced Raman spectroscopy (SERS) technique for the analysis of organic dyes.In the present work, a new method is presented, based on the use of a SERS probe made of agar-agar coupled with silver nanoparticles, for a non-destructive and minimally invasive micro-extraction of dyes from textiles. Ag-agar gel has been tested first on textile mock-ups dyed with alizarin, purpurin and carminic acid. SERS measurements have been performed adopting laser light excitations at 514.5 and 785 nm of a micro-Raman setup. Highly structured SERS band intensities have been obtained. After having verified the safety of the method by colorimetric, X-ray fluorescence and attenuated total reflectance Fourier transform infrared techniques, a real case, a pre-Columbian piece of textile, have been investigated by Ag-agar gel. This cutting-edge method offers new possibilities for a sensitive and non-destructive analysis of fluorescent materials. Figure 8. Comparison among SERS spectra of alizarin (8a-d), purpurin (8b-e) and carminic acid (8c-f) extracted from textiles by means of Ag-agar gel procedure, collected with diode laser excitation at 785 nm (8a-b-c) and argon ion laser excitation at 514.5 nm (8d-e-f).Detection of red organic dyes in Ag-agar gel

Tailored micro-extraction method for Raman/SERS detection of indigoids in ancient textiles

“…Agar gel was synthesized according to the procedure previously published [10]. In brief, 0.2 g of agar-agar in flakes was mixed in a beaker with 10 mL of water or with silver colloidal water dispersion to obtain the agar gel or the Ag-agar gel, respectively.…”

“…Moreover, degradation processes or bad state of conservation of the art object may further affect the analyses of the blue dye. In the last decade, the successful application of the high sensitive surface enhanced (resonance) Raman spectroscopy [SE(R)RS] for the detection of organic dyes in works of art has strongly improved the possibility of identifying fluorescent organic dyes according to minimal invasive [10][11][12][13][14] and microdestructive approaches [15][16][17]. Up to the present, the majority of the developed SERS procedures dealt mainly with the detection of red and yellow dyes [15][16][17][18][19][20][21][22][23][24][25][26], whereas only a few works have investigated the characterization of indigoids by means of SERS/SERRS.…”

Hyper-Spectral Acquisition on Historically Accurate Reconstructions of Red Organic Lakes

“…Despite promising efforts have been developed [4,5], the non-invasive techniques usually used in the identification of other classes of artists' materials are generally not adequate in this case [3]. UV-Vis-NIR Fiber Optic Reflectance Spectroscopy (FORS) could be in principle used for the identification of the organic colors since it is very sensitive to this class of pigments, and allows collecting information in a non-invasive way [3].…”

Raman Spectroscopy of cultural heritage Materials: Overview of Applications and New Frontiers in Instrumentation, Sampling Modalities, and Data Processing

“…To this end, a small but growing number of papers have been published demonstrating the use of flexible substrates based on acrylic gels [182,183], methylcellulose pastes [119], gelatin [120], or agar-agar gel [187,241], optionally loaded with a mild micro-extractant, often based on ethylenediaminetetraacetic acid (EDTA) [240]. The analytical procedure either involves mixing the gel with nanoparticles, or using the gels to extract a minute and nearly invisible amount of dye for later analysis with SERS after deposition of colloidal silver particles on the face that was previously in contact with the artifact.…”