纳米二氧化钛荧光粉末显现潜在手印研究

Detection of Latent Fingerprint Using Fluorescent Nano-dye/TiO2 Powder

目的使用荧光染料包覆纳米二氧化钛颗粒,制备具有荧光效果的纳米二氧化钛粉末材料,并探索应用纳米二氧化钛荧光粉末显现潜在手印的方法。方法使用实验室合成的二酰亚胺染料与纳米二氧化钛微粒按照一定质量比混合制备形成荧光粉末,通过扫描电子显微镜对其进行表征,观察颗粒结构特征。在玻璃、瓷砖、透明塑料片、彩色塑料包装、易拉罐5类非渗透性客体上捺印手印,观察纳米二氧化钛荧光粉末对不同非渗透性客体上新鲜潜手印的显现效果。分别在5种客体上制作遗留时间为1、4、7、15d的手印样本,考察遗留时间对纳米二氧化钛荧光粉末显现自然陈旧手印效果的影响。将新鲜手印置于标准大气压100℃条件下分别加热1~72h,使用纳米二氧化钛荧光粉末显现,考察其对高温老化手印的显现效果。结果纳米二氧化钛荧光粉末为粒径100~200nm的圆形颗粒;在蓝绿光激发下可发出较强的荧光,能显现多种非渗透性客体上的新鲜手印,与背景反差明显并且能显著降低复杂背景对手印纹线的影响;显出新鲜手印中80%以上具有鉴定条件。纳米二氧化钛荧光粉末对遗留15d以内的陈旧手印仍具有较好的显现效果。100℃高温环境对手印显现效果没有明显影响。结论纳米二氧化钛荧光粉末经济、环保,显现操作简单,易于推广。

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 15 d 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 515 nm.Results Observation of the prepared powders using SEM shows that the dye-coated particles＇ size varies from 100 to 200 nm in diameter.The fluorescent dye/TiO2 powder was light pink particles under white light.Illuminated at 515 nm,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 72 h 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 515 nm 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.