News from Diagnostic World: identification of organic colorants in fibers, paints, and glazes by Surface Enhanced Raman Spectroscopy

 

Written by Tiziana Pasciuto

Translated by Sarah Fortunée Tabbakh

Italian Version here

I have recently talked about the Raman Spectroscopy, focusing on the advantages and disadvantages of this non-invasive diagnostic technique (click here to refresh your memory). As you may remember, one of the limitations of the technique was the phenomenon of the fluorescence that occurs in organic samples. The analysed substance reemits the received electromagnetic radiations; the Raman signal, rather weak in itself, is easily hidden by the fluorescence, which obstructs the identification of the analysed substance. 

How can we face this problem which often limits the identification of some pigments, binding agents and varnishes? With the SERS, acronym that stands for Surface Enhanced Raman Spectroscopy. 

The Raman Spectroscopy enhanced by surfaces is a technique that, through chemical and electromagnetic mechanisms, reduces the fluorescence characterised by the substances and, at the same time, enhances the Raman signal. This discovery dates back to 1974, when scientist Fleischmann and collaborators observed for the first time the enhanced Raman phenomenon of the pyridine adsorbed on a rugged surface of a silver electrode. The technique therefore consists in the realisation of a substrate, in a solid or colloidal state, inside which can be found nanoparticles of silver that enable the enhancement of the Raman signal. This substrate is then positioned on the sample to analyse and we can then proceed to the usual analysis using the Raman spectroscopy. Many studies have been carried out, but I have selected a 2010 article taken from a journal with a significant Impact Factor (amounting to 22!): “Accounts of Chemical Research”, DOI: 10.1021/ar100019q. 

I chose this article for different reasons. Firstly, I find that the article confers to the curious and untrained reader a general view of the history of SERS, of the different substrates used and of their advantages, as well as future prospects of an ongoing developing technique. Moreover, it stresses on the application and potential of the technique using four case studies in the field of Cultural Heritage. The cases are diverse in material and era and include archaeological artefacts, ancient textiles, paintings and pastels (both analysed as is and in the work of art). 

If you are curious and you have the needed authorization or the membership to the journal “Accounts of Chemical Research”, you will find here the link to the article: https://pubs.acs.org/doi/abs/10.1021/ar100019q.

The technologies applied to cultural heritage are ever-developing: join us to find out what they are! 

- Articolo sulla Spettroscopia Raman, scritto da Tiziana Pasciuto e pubblicato nel blog il 29/05/2017: http://researcheritage.blogspot.it/2017/05/La-Spettroscopia-Raman.html 

- M. Fleischmann, P. J. Hendra, A. J. McQuillan, Raman spectra of pyridine adsorbed at a silver electrode, Chemical Physics Letters, 1974: http://www.omel.ethz.ch/content/dam/ethz/special-interest/mavt/process-engineering/omel-dam/documents/handouts/m-fleischmann.pdf 

- A. Campion, P. Kambhampati, Surface-enhanced Raman scattering, Chemical Society Reviews, 1998: http://pubs.rsc.org/en/content/articlelanding/1998/cs/a827241z#!divAbstract 

- R. Aroca, Surface-enhanced Vibrational Spectroscopy, John Wiley & Sons Ldt, 2006: http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0471607312.html