APPLICATION OF SURFACE-ENHANCED RAMAN SCATTERING BASED ON COLLOIDAL SILVER NANOPARTICLES FOR PEN INKS CLASSIFICATION IN FORENSIC DOCUMENT EXAMINATION
Questioned documents are documents from suspicious source or authenticity, that may involve not only in forgery cases but also in homicides, burglaries, robberies and other crimes. In 2015, the Court of Justice in Thailand reported that 95% of counterfeited offences were document cases, especially written document, that trend to increase in number of cases every year. Therefore, an alternative scientific method to characterize ballpoint pen ink on written document employing colloidal surface-enhanced Raman scattering (SERS) effect was developed in this work. The colloidal silver nanoparticles (AgNPs) were synthesized using green method and effects of several parameters on colloidal formation and SERS effectiveness were investigated. The results showed that the AgNPs with an average diameter of 37 ± 1 nm can be used as SERS material for in situ analysis of ballpoint pen inks on document. The strongest Raman fingerprints of pen inks were achieved by characterization using Raman spectrometer with a laser wavelength of 532 nm. The results showed that reported AgNPs colloid could be a powerful SERS nano-amplifier for water-gel based inks analysis. Furthermore, it is a convenient, rapid, and non-destructive method for forensic analysis of written pens on questioned document.
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