Lasers, nanoparticles and wine: white wine identification with SERS

By Alois Bonifacio

Wine counterfeiting is a problem. How to make sure that the wine inside a labeled bottle truly is that wine? Is there such a thing as a unique wine “signature” or “fingerprint”? Of course there is, each wine is unique in its complexity. It’s just that this unique signature is not easy to get. In fact, a method to get such signature should be accurate, reproducible, but also easy and quick to use, and possibly relatively inexpensive.
We thought that perhaps, an analytical technique such as Surface-Enhanced Raman Spectroscopy (SERS) could be used for that purpose. SERS is an optical spectroscopy in which a low-power laser is shone on a sample, and silver or gold nanoparticles are added to the sample as tiny “enhancers”, to boost up the intensity of the scattered light.

 

By analyzing this light scattered by the sample, one can get information about the chemical composition of the sample. In particular, the chemical species adsorbed on the surface on the metallic nanoparticles will yield an intense spectroscopic signal. When used on chemically complex samples, the spectra obtained can be though as a sort of unique spectroscopic fingerprints. Moreover, the method is particularly attractive, as it is rapid, relatively inexpensive (if compared with gold standards) and using portable instrumentation.

Having the luck of living and working close to a region, the Colli Orientali in Friuli, renowned for its white wines such as Friulano, Ribolla and Sauvingon, we thought that these wines would have been excellent samples to test this approach. In collaboration with dr. Francesco Zanuttin, a biologist and ideator of the study, Giovanni Bigot, a wine expert, and dr. Antonella Calabretti, a food science expert, we published a study in Talanta (volume 203, 2019, pages 99-105) in which we analyzed with SERS nine different white wines from Colli Orientali. In particular, we selected 1 Friulano, 1 Ribolla and 1 Sauvignon from three different producers, to see if the technique was capable to distinguish between the wines produced by wineries only few hundreds of meters apart. Results were rather surprising: SERS spectra from different wines are different from each other, and can be used to identify each wine with a remarkable accuracy (around 90%). We also realized that SERS spectra mainly depends from specific wine constituents such as purines (e.g. adenine) and glutathione, and that wines can be distinguished on the basis of these two components, when taken together. Although this is still a preliminary study, whose results need to be validated on a larger number of samples, it suggests that indeed SERS could be a method used to get a unique “signature” of a wine. Preliminary, unpublished results suggest that the same method could work with red wines as well, but this is still a work in progress.

Those interested in a longer length report can download the working paper at:
https://www.sciencedirect.com/science/article/pii/S0039914019305089

 

SERS spectra for the 9 different wines: Friulano (F), Sauvignon (S) and Ribolla (R) from producers A,B and C. Reproduced with permission.

PCA scores plot for the first two principal component of the spectra, showing how the samples from the same wine cluster together, and can be distinguished from other wines. Reproduced with permission.

Alois Bonifacio, after getting his Ph.D. in Chemistry at the Vrije Universiteit in Amsterdam (The Netherlands) in 2007, landed as a PostDoc at the University of Trieste (Italy), where he is now Associate Professor of Chemistry. Since his Master, he always worked on bioanalytical applications of Raman and SERS, with interests ranging from basic research on CYP enzymes and other hemoproteins, to the Raman imaging of biological tissues and the analysis of biofluids using SERS. He is also interested in nanotechnology, especially from the perspective of nanostructured metal surfaces as SERS substrates, as well as in multivariate analysis of spectroscopic data.