摘要
Abstract
Objective To explore a new approach for developing latent fingerprints by using fluorescent titanium dioxide nano-particles. Methods Titanium dioxide nano-particle was coated with fluorochrome and the morphological feature was observed by scanning electron microscope (SEM). Five kinds of non-porous surfaces, including glass, transparent plastic, colored plastic, tile, and can were used in this experiment. Fingermarks were deposited after wiping fingers over the forehead in succession and then pressing them onto substrates. The fluorescent powder was applied to fingermarks deposited on the surfaces. The fingermarks were stored for 1, 4, 7 and 15d or heated at 100℃ for 1~72h before treated. The samples were then observed in the luminescence mode using a Polilight alternative light source with the emission set at excitation wavelength of 515nm. Results Observation of the prepared powders using SEM shows that the dye-coated particles’ size varies from 100 to 200nm in diameter. The fluorescent dye/TiO2 powder was light pink particles under white light. Illuminated at 515nm, TiO2 particles coated with fluorescent dye exhibited strong fluorescence. When latent fingerprints detected with this fluorescent powder, particles could be selectively adhered to the latent fingerprint deposit. Fingerprints developed with fluorescent dye/TiO2 showed strong orange-red luminescence and clear details of ridge. On several nonporous substrates, the new powder gave a lower background and thus better contrast in developed fingerprints. Colored surfaces were also tested and the results demonstrated the advantages of the fluorescent powder with better contrast. Storage time of fingerprints did not make significant difference in the quality of developed fingerprints on glass. The fluorescent dye/TiO2 powder gave satisfactory results when applied to 15-day fingerprints retained on substrates of glass, transparent plastic and cans. The enhancement for detail was slightly less than that with fresh prints, but the powder still revealed clear images. While for colored plastic, the image of older marks (>7d) developed by fluorescent dye/TiO2 powder showed less ridge details. Fingerprints on tile developed by fluorescent dye/TiO2 powder showed strong fluorescence, but the image of older marks became indistinct over time. When the fingerprints heated for 1~72h were developed with the fluorescent dye/TiO2 powder, the quality of developed fingerprints was as for fresh fingerprints. However, a slight reduction in fluorescence intensity was observed towards the 72h setting as fingerprint deposit dried out and lost its stickiness. Conclusions Fluorescent nano-dye/TiO2 powder is a new developing method that can be applied to develop fresh as well as aged latent fingerprints on nonporous substrates without background color requirements. This method is very sensitive and selective; the fluorescence can be excited at 515nm and observed through an orange-red long-pass filtering barrier. This fluorescent powder is easy to use, low-cost and non-toxic, it can be used for developing latent fingerprints.关键词
手印/荧光粉末/二氧化钛Key words
fingerprints/fluorescent powder/titanium dioxide分类
社会科学
