Detection of latent fingerprints on counterfeit currency
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The unambiguous identification of a counterfeiter by fingerprint evidence hinges on the determination whether the fingerprint was placed on the counterfeit note before (FB) or after inking (FA). Three counterfeiting methods, including color copying , offset printing and Inkjet printing have been investigated. A number of techniques, including 5-methoxyninhydrin/ZnCl2, DFO, DMAC, physical developer, colloidal gold, membrane transfer, vapor development, and finally, Eu-DTPA/OP have been explored in an attempt to distinguish between fingerprints on counterfeit currency before and after the inking. Most methods fail to show a difference between FB and FA fingerprints because of the permeability problem of the inks. However, the lipid-sensitive Eu-DTPA/OP procedure partially overcomes the permeability problem and shows substantial difference between FB and FA fingerprints for color copying. There are subtle differences between before and after fingerprint fluorescence spectra (both 5-methoxyninhydrin/ZnCl2 and Eu-DTPA/OP). Given that one has to contend with finger contamination, the spectroscopy at present may not be practically useful, but it shows potential if proper rare-earth-based strategies are used.