蔬菜粉末荧光光谱测定及其在手印显现中的应用

对遗留在客体表面的手印进行提取和鉴定是侦破案件的重要依据。对在犯罪现场发现的手印进行固定提取时，首先应该使用没有破坏性的光学无损检验技术。实践表明光学无损检验技术对于绝大部分光滑客体上的手印都能取得很大的反差和较好的纹线细节，而对于光滑度较差的客体上的手印则需要使用有损的物理法和化学法对指印进行固定提取。其中粉末法和熏显法在手印显现中得到了广泛的应用，但是常用的绝大部分粉末和熏显物质对长期从事手印显现的工作人员身体有较大的毒副作用。而且绝大部分常用的荧光粉末需要在紫外线的激发下产生荧光，紫外线激发手印产生荧光的同时也常会激发承痕客体产生很强的背景荧光，进而降低了手印与背景的反差。因此寻找一种成本低廉、无毒无害、操作简单和应用性广泛的手印显现方法是当务之急。研究了三种无毒无害、成本低廉的蔬菜粉末的荧光性能，并且将其应用于手印显现中。首先通过荧光分光光度计测定西蓝花粉末、菠菜粉末和紫菜粉末的荧光激发光谱和荧光发射光谱。通过荧光测定发现，西蓝花粉末的荧光比菠菜粉末和紫菜粉末的荧光强很多，所以选择西蓝花粉末显现犯罪现场常见的疑难客体表面汗潜手印。实验结果表明：（1）西蓝花粉末、菠菜粉末和紫菜粉末都能发出荧光，荧光激发光谱峰值都在417 nm，荧光发射光谱峰值都在678 nm，其中西蓝花粉末发出的荧光最强。（2）将西蓝花粉末用于多色图案干扰的非渗透性和渗透性客体上的汗潜手印的显现中，在415 nm的紫光的照射下能够发出明亮的红色荧光。拍照荧光指印时在镜头前加上透过中心波长为680 nm左右的窄带通干涉滤光镜，结果显示手印纹线与背景反差强烈，纹线清晰连贯，消除背景的干扰。（3）与传统的荧光粉末显现法相比，该显现方法具有较高的显现灵敏度。（4）有些客体背景图案在415 nm的紫光的照射下也有发光，但与西蓝花粉末的非常强的荧光相比，背景的荧光弱得多，所以使得手印与背景之间形成了较大的反差并且纹线的细节特征清晰。（5）粗糙客体上手印的显现也获得了很大的反差，粗糙的背景没有对纹线形成干扰而形成了清晰连贯的纹线。（6）实验中使用的市售的西蓝花粉末具有颗粒细小、吸附能力强等特点，能够促进手印物质与西蓝花粉末之间的选择性吸附，进而进一步提高手印显现的灵敏度。

Study on the Fluorescence Spectral Characteristics of Vegetable Powders and Their Application in Development of Latent Fingerprints

It is an important basis for detecting cases to develop the latent fingerprints left on the substrates and make individual identification.Optical examination techniques which are nondestructive should be applied first when developing the latent fingerprints found at crime scenes.The practice shows that high contrast and fine ridge detailcan beobtained when applying optical examination techniques to develop the fingerprints on the most smooth substrates,while the physical and chemical methods are needed to develop the fingerprints on substrates of poor smoothness.Among them,the methods of powder dusting and fuming have been widely applied in the development of latent fingerprints.However,the long-term health of forensic technicians has been damaged seriously by most fluorescent powders and fuming materials.In addition,the most commonly employed fingerprint luminescent powders can fluoresce when excited with ultraviolet light.At the same time,the backgrounds can also fluoresce under the excitation of ultraviolet light,which results in low contrast between fingerprint and background.Therefore,it is an urgent task to find a low-cost,non-toxic,easy-to-operate,and widely used method for developing fingerprints.In this paper,the fluorescence characteristics of three non-toxic and inexpensive vegetable powders were studied to apply them to the development of fingerprints.Firstly,the fluorescence excitation spectrum and emission spectrum of three kinds of vegetable powders(broccoli powder,spinach powder and nori powder)were measured through fluorescence spectroscopy(FS).It was found that the fluorescence of broccoli powder was much stronger than that of spinach and nori powder by fluorescence measurement.Therefore,the broccoli powder was chosen to develop the latent fingerprints on trouble some substrates commonly encountered at crime scenes.The experiment results showed that:(1)All the three kinds of powders could fluoresce,and their peak fluorescence excitation wavelengths were all 417 nm,and the peak fluorescence emission wavelengths wereall 678 nm.Among the three kinds of powders,the emission intensity of broccoli powder was the highest.(2)In developing latent fingerprints on a range of highly patterned,colored non-porous and porous substrates,the broccoli powders could emit bright red fluorescence under violet 415 nm illumination.A narrow bandpass interference filter with a central wavelength of around 680 nm was used in front of the lens when photographing the fluorescent prints,and the results showed a high contrast between the fingerprint and the background with fine ridge detail and less interference.(3)Compared with the conventional luminescent powders,broccoli powder had higher development sensitivity.(4)Some backgrounds under violet 415 nm illumination could also fluoresce,but the background fluorescence was weak compared with the strong fluorescence of broccoli powders,revealing high contrast fingerprints with excellent ridge detail.(5)The fluorescence of the fingerprints on rough backgrounds created a sharp contrast,and the rough backgrounds did not interfere with fingerprint ridge,which was clear and coherent.(6)The commercially available broccoli powders used in the experiment had the characteristics of fine particles and strong adsorption ability,which could invoke favoured adhesion characteristics upon contact with fingerprint ridge residues,improving the sensitivity of fingerprint development.