Discrimination between authentic and counterfeit banknotes using Raman spectroscopy and PLS-DA with uncertainty estimation

In the present work, Raman spectroscopy and chemometric tools were explored as an analytical method to discriminate authentic and counterfeit Real banknotes. The analysis was based on the characterization of inks used to confect the banknotes. Multivariate analysis was required for data analysis, since the colors present in the banknotes are a mixture of pigments and the Raman spectra is complex and not totally resolved. Original and counterfeit R$ 50 banknotes were analyzed by Raman spectroscopy without any sample preparation and three different areas were selected for study: chalcographic, orange and red inks. In this study, only the results for the chalcographic ink will be present. The classification method PLS-DA was employed to discriminate authentic and counterfeit banknotes, as well as the counterfeit type. The reliability of the results was calculated using the re-sampling bootstrap technique. The samples classified as counterfeit banknotes by the PLS-DA model had been apprehended by local authorities and classified as fake by classical forensic approaches, based on sensory tests and optical inspection by a specialist. PLS-DA was used for the development of a procedure, that could be used by non specialist operators and can also analyze new samples of R$ 50 banknotes, classifying them with reliability and estimating uncertainty. In the proposed method all fake and not fake banknotes used to validate the analysis were correctly classified. The procedure could be used as a complementary method to classical forensic inspection, offering fast, non-destructive, robust analyses with the possibility of in situ analysis using a portable instrument. (C) 2012 Elsevier B.V. All rights reserved.