Dequenching of infrared luminescence

“Dequenching” has been observed in infrared luminescence as well as ultraviolet fluorescence (Gupta et al., Forensic Sci. Int., 12 (1978) 61 – 64). Thin-layer chromatographic separations of non-luminescing inks can reveal luminescent bands. This dequenched luminescence can also be observed by spot tests with solvents and under transparent adhesive tape.     

签字笔水、圆珠笔油红外发光特性的研究

目的记录不同激发光、接收滤光镜下,各种油墨红外发光强弱的程度,为文字检验提供基础性的研究。方法用多波段光源中510~650nm单色光激发各种油墨样本,全波段物证检验CCD系统记录样本在530~950nm接收滤光镜下出现的红外发光图像。结果多数油墨在接收滤光镜到达800~850nm时,呈现出强烈的红外发光状态,并随接收波段的上升而开始衰减。结论可利用某些油墨的发光与否,发光强与弱的特性,检验案件中涂改和涂抹字迹。     

On the detection of fingerprints by laser excited luminescence

Two surveys were carried out to determine the percentage of latent fingerprints detectable by their inherent luminescence under laser illumination. Less than one-fifth of 240 samples each containing four prints on paper gave luminescent prints. The luminescence from these was weak and only detectable under close scrutiny. Similar results were obtained for 120 samples each containing one print on glass. Forty-one of the samples showing no luminescence were sprayed, approximately one month after deposition, with a solution containing the fluorescent tagging agent 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD chloride). After treatment with NBD chloride, 37 of these samples gave luminescent prints, many of which were intensely luminescent and contained good ridge detail.     

Forensic applications of chemical imaging: latent fingerprint detection using visible absorption and luminescence

Chemical imaging technology is a rapid examination technique that combines molecular spectroscopy and digital imaging, providing information on morphology, composition, structure, and concentration of a material. Among many other applications, chemical imaging offers an array of novel analytical testing methods, which limits sample preparation and provides high-quality imaging data essential in the detection of latent fingerprints. Luminescence chemical imaging and visible absorbance chemical imaging have been successfully applied to ninhydrin, DFO, cyanoacrylate, and luminescent dye-treated latent fingerprints, demonstrating the potential of this technology to aid forensic investigations. In addition, visible absorption chemical imaging has been applied successfully to visualize untreated latent fingerprints.     

A further study to investigate the detection and enhancement of latent fingerprints using visible absorption and luminescence chemical imaging

This study investigated the application of chemical imaging to the detection of latent fingerprints using the Condor macroscopic chemical imaging system (ChemImage Corp., Pittsburgh, USA). Methods were developed and optimised for the visualisation of untreated latent fingerprints and fingerprints processed with DFO, ninhydrin, cyanoacrylate, and cyanoacrylate plus rhodamine 6G stain. The results obtained with chemical imaging were compared to the detection achieved using conventional imaging techniques. The Condor significantly improved the detection of many prints, especially those that might be considered poor quality or borderline prints. Prints on newspaper treated with ninhydrin and DFO, and prints on white and yellow paper treated with ninhydrin, benefited the most from chemical imaging detection. In many cases, fingerprints undetectable using conventional imaging techniques could be visualised with chemical imaging. Ridge detail from untreated prints on yellow paper was also detected using the Condor. When prints of high quality were examined, both detection techniques produced quality results. The results of this project demonstrate that chemical imaging offers advantages over conventional visualisation techniques when examining latent fingerprints, especially those that would be considered difficult, such as weak prints or prints on surfaces that produce highly luminescent backgrounds. Standard testing procedures for the detection and enhancement of fingerprints by chemical imaging are presented and discussed.     

Use of styryl 11 and STaR 11 for the luminescence enhancement of cyanoacrylate-developed fingermarks in the visible and near-infrared regions

In current casework, most post-cyanoacrylate stains rely on luminescence emission in the visible region (400-700 nm). While traditional stains such as rhodamine 6G work well under most circumstances, some surfaces may generate background luminescence under the same conditions. Detection in the near-infrared region (NIR > 700 nm) has shown to be effective in minimizing the interferences from such surfaces. The laser dye styryl 11 generated strongly luminescent fingermarks when applied after cyanoacrylate fuming on all surfaces tested. When compared to rhodamine 6G, the dye was superior only when viewed in the NIR. Styryl 11 was subsequently combined with rhodamine 6G, and the mixed stain formulation (named StaR 11 by the authors) induced stronger luminescence compared with styryl 11 alone with an ability to visualize in both the visible and NIR regions. Reliable and consistent results were obtained when using either styryl 11 alone or the STaR 11 mixture. The enhancement achieved did not otherwise vary depending on the source of the fingermark secretions. With visualization possible in both the visible and NIR regions, the styryl 11/rhodamine 6G mixture showed significant potential as a post-cyanoacrylate stain.     

Differentiation between inks of the same brand by infrared luminescence photography of their thin-layer chromatograms

A case is reported involving a U.S. Treasury check with an altered amount payable. The ink in the alteration and the ink in the endorsement signature were compared with ink from three Skilcraft ball pens all having Skilcraft black ink ball pen refills. Infrared luminescence photography of their thin-layer chromatograms revealed differences between the inks in the three pens.     

In situ luminescence spectroscopy with multivariate analysis for the discrimination of black ballpoint pen ink-lines on paper

A novel approach to the non-destructive discrimination of black, ball-point pen ink-lines on paper, has been developed which uses a standard luminescence spectrometer coupled with multivariate statistical analysis. The application of Principal Component Analysis (PCA) to these data-sets, followed by linear regression of the loadings, not only facilitates separation of the ink luminescence from that of the paper, but also allows a direct comparison between two ink lines on documents. This data reduction means that such a comparison can be done on an effectively univariate basis whereby a straightforward statistical comparison is made between two numbers, each characteristic of an ink. Thus the question, in the forensic context, of whether two ink-lines are indistinguishable may be answered with a particular statistical confidence and the method shows significantly better discrimination, for the pens studied, than conventional forensic investigative techniques involving the luminescence imaging of writing using filtered light.     

Effect of "Fit" dishwashing detergent from former Eastern Germany (GDR) on luminol luminescence

The forensic luminol test is used to screen large areas for the presence of blood. The heme-induced reduction of hydrogen peroxide is coupled to the oxidation of luminol resulting in luminescence. However, photographic documentation of the relatively weak and short-lived luminescence is difficult and luminol is now often replaced by other chemicals. In this study, we investigated reports from the Rostock police department that the addition of "Fit", a dishwashing detergent from former Eastern Germany, could both intensify and prolong the luminescence of luminol on blood stains. Even though this effect was reported only for the original composition of Fit but not the currently sold version, we found that both the old and the new version of Fit increase the brightness of the luminescence while decreasing its duration. This may be due to detergents in the dishwashing liquid, which permeabilize the plasma membrane of the erythrocytes, exposing the Fe3+ inside the cell and speeding up the entire reaction. We did not find any evidence of special ingredients in the old version of Fit that would cause both the increased brightness and prolonged duration of luminescence as reported by the Rostock PD.     

对"牛吃麦"案例的另一维度的解释——英、美土地制度和财产制度的变迁

科斯定理是从经济效益的角度来分配权利的,它的"拍卖式"法律价值取向贯穿于美国土地制度与财产制度的发展历程.在与科斯定理相关的"牛吃麦"案例上,美国初始选择了"圈出"规则,后又转向"圈入"规则,其规则的变动始终遵循着"经济效益最大化"原则;而英国自始至终选择了"圈入"规则,早期是为了维护公共财产利益,之后是为了维护私有财产利益,在这过程中,"权利保护原则"是其不变的宗旨.科斯定理纯粹从经济效益的角度来解释有着相同法治渊源与传统的英、美两国在"牛吃麦"案例上所适用规则的差异性,欠缺历史维度的法律分析.