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A new material that produces less background noise and higher contrast is being developed as a new fingerprinting powder for forensics. The highly fluorescent dye was synthesised using oleylamine combined with a perylene dianhydride compound and characterised by UV, NMR, and fluorescence spectroscopies before being loaded on to titania nanoparticles. Writing in the December issue of Forensic Science International, Andrew McDonagh and colleagues at the University of Technology, Sydney and the Australian Federal Police, in Canberra, explain how fingerprints remain one of the most commonly admitted pieces of evidence in any crime investigation. Fingerprints, or marks, can be visible to the naked eye or latent. If a forensics expert has lifted a latent mark, then chemical or other enhancement is required to reveal the print adequately. McDonagh and his colleagues have now investigated the potential of a new approach to developing finger marks on typical non-porous surfaces such as glass, plastic, metal, and gloss-painted surfaces. The researchers explain that for fingerprints on non-porous surfaces, powdering remains the technique of choice for revealing a finger mark at a crime scene. It is the nature of the powder that can be the difference between a successful prosecution and an acquittal. Using a powder that adheres to the oily or moist residue left by a suspect and forms a visible and stable print for photographing is critical. The team has turned to nanocrystalline titania (TiO2). This material has been widely studied because of its many and varied optical, electrical, and photocatalytic properties. Previous researchers have demonstrated that suspended in methanol titania particles can enhance bloody prints on non-porous and semi-porous surfaces while others have shown titania can be used to develop prints on wet surfaces. It is possible to apply it as a paste with a brush, spray from solution, or even to submerge a piece of evidence in the reagent itself. Others have shown that it can develop prints on both the outer and sticky surface of dark coloured electrical tapes and duct tapes. However, it is its behaviour in adsorbing other compounds and to act as an optical brightener that could be of interest to the forensic scientist. McDonagh and colleagues have investigated the possibilities of using titania in conjunction with the highly stable dye stuffs, perylene and perylene diamide. These common synthetic dyes come in a range of colours from red to violet and even black. More pertinent, they are highly fluorescent and photostable. "We anticipated that combining titania particles with a robust fluorescent dye bearing lipophilic substituents may increase the utility of titania in latent finger mark detection," the researchers explain. To this end, the team has synthesised and characterised a new perylene diimide derivative from oleylamine and 3,4,9,10-perylenetetracarboxylic dianhydride. They then coated titania particles with this new dye. They have found this composite material to exhibit strong fluorescence at 650-700 nm (red) under excitation at 505 nm (greeny-blue). In tests to reveal prints on glass surfaces, they found that their new powder produce finger mark images with so-called tertiary-level detail. The images showed very little background staining that would otherwise distort the print, something that was apparent with commercially available powders. Compared with current magnetic fluorescent powders, the new powder was slightly weaker in fluorescence intensity but produced significantly less background development, resulting in good contrast between the finger mark and the substrate. The only surface from which fingerprints could not be obtained with any clarity was a painted wood surface. The team is currently investigating other metal oxide particles for use with these and other surfaces. Related links: The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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