Documentoscopy by atomic force microscopy (AFM) coupled with Raman microspectroscopy: applications in banknote and driver license analyses

Document examination to determine document authenticity is an important field in forensic science. Methods of counterfeiting have become sophisticated, so the development of informative and effective tools for questioned document examination becomes necessary and challenging. Atomic force microscopy (AFM) and Raman microspectroscopy have been shown to be advantageous, allowing the comparison of inks, the sequencing of crossing lines, and providing physicochemical information about the nature of the paper and of the ink deposition mechanism. Herein, AFM and Raman techniques are explored for the analysis of both authentic and counterfeit Brazilian driver licenses, and national and international banknotes. For AFM results, parameters, such as roughness and topographic profiles of the chalcographic region of banknotes and Brazilian driver licenses, are sufficient to visually discriminate between authentic and counterfeit documents. However, statistical analysis using the Student's t-test showed that the asymmetry (SSK) values obtained from series numbers and micro-letter regions identified the counterfeiting. Compared to the topographic profile obtained for homemade banknotes produced by different printers (inkjet and LaserJet), the AFM technique indicated that the paper used to counterfeit the Brazilian driver license and the real banknote was an "office" type with inkjet printing. For Raman spectroscopy results, bands of phthalocyanine, and diarylide (diazo) pigments, and carbon black were identified in authentic documents, whereas for counterfeit documents, only a high fluorescence was observed. The obtained data were reproducible via the video spectral comparison (VSC) technique, typically used by forensic police laboratories.