Utilizing Crime-lites for the Visualization of Fluorescence from STK Sperm Tracker


October 20, 2021 — The identification of a body fluid detected on a piece of forensic evidence can be critical to an investigation. Identification of the location of a body fluid not only allows forensic scientists to perform crime scene reconstructions, but also provides further support in identifying the most appropriate samples for DNA analysis.

STK Sperm Tracker™ was developed in a collaboration between AXO Science and the French National Institute of Scientific Police (INPS). Spermtracker technology is commercially available in multiple formats: a lab-based paper or a spray which can be utilized directly at a crime scene or directly on skin. If a semen stain is present on the substrate, a UV-A forensic light source can be applied to visualize the fluorescent emission from the STK paper. A positive result for semen is indicated by a clear and bright-blue fluorescent result on the STK paper.

A collaborative study has been conducted alongside L’Institut de Recherche Criminelle de la Gendarmerie Nationale, with the aim to determine whether Foster + Freeman UV Crime-lite® light sources are suitable for promoting visualization of fluorescence from STK paper. The manufacturer specification recommends that a UV light source with a peak wavelength of 365-366nm should be used to promote fluorescence emission from their STK products. All Crime-lite light sources featured within this study utilize UV with a peak wavelength of 365nm (bandwidth 350-380nm). Samples were initially visually checked throughout the study with the Crime-lite 82S UV light source and then illuminated and imaged with both the Crime-lite Auto and the Crime-lite ML-Pro.

Crime scene illumination and imaging
The Crime-lite Auto is the most integrated, comprehensive, and compact forensics digital camera solution in existence. Combining the latest forensic imaging technology with high-intensity, multi-spectral illumination, the Crime-lite Auto is a complete solution for the search, detection, and capture of evidence.

Crime Scene Illumination
The Crime-lite 82S UV offers levels of illumination and ease of use that will almost certainly increase the quantity and value of evidence detected. Every Crime-lite 82S UV features 16 LEDs hand-picked for brightness and wavelength accuracy, ensuring consistent performance and a non-destructive method for detecting evidence.

Laboratory Illumination and Imaging
The Crime-lite ML Pro is part of a new generation of evidence screening tools, built to meet the demands of high-throughput forensic laboratories tasked with processing large quantities of evidence. With fully integrated UV-Vis-IR illumination and an "intelligent optics" imaging system, the ML Pro can be used to mark up evidence, detect the presence of bodily fluids, and can create an integrated examination report ready for court.

Test Conditions
The study was conducted at Foster + Freeman Headquarters in Evesham, UK. Ten samples were provided by L’Institut de Recherche Criminelle de la Gendarmerie Nationale for the collaborative study: five single-source samples containing semen on fabric and five mixed-source samples containing semen and blood on fabric. Foster + Freeman provided a single-source control sample of semen on fabric.

The STK paper was cut to twice the dimensions of the fabric to be analyzed. The unplasticised surface of the paper was then wetted uniformly with distilled water using a spray bottle with the paper briefly suspended to remove any excess water. The fabric material was placed onto the wetted side of the paper, before the STK paper was then folded in half ensuring the fabric was sandwiched between it. Pressured was applied to the STK paper utilizing a weighted object of 5 kg and the sample was then left for a period of three minute within the pressurized environment. After the period of three minutes, the weight was removed from the sample and the fabric material was imaged.

The Crime-lite 82S UV light source was utilized first to illuminate the fluorescence emission from the STK paper so a visual assessment could be made as to whether a positive result had been achieved. The samples were then illuminated and imaged with both the Crime-lite Auto and the Crime-lite ML-Pro. The Visible Pass filter (GG420 Long pass) was utilized on the Crime-lite Auto and the GG420 Long pass filter was applied on the Crime-lite ML-Pro to visualize the UV fluorescence being emitted by the STK paper in the images.

All ten samples provided by L’Institut de Recherche Criminelle de la Gendarmerie Nationale produced a fluorescence signal emitted from the semen staining which could be observed when viewed visually with the Crime-lite 82S UV light source and when imaged with the Crime-lite Auto and the Crime-lite ML-Pro. The Foster + Freeman control sample also provided an observable fluorescence reaction from semen staining when viewed under the same three light sources. Some dark staining was observed upon illumination on some of the semen and blood mixtures, although this did not appear to interfere with the positive results attained from these samples.

When illuminated with a Foster + Freeman Crime-lite light UV sources (365nm), the fluorescence emission from STK can be visualized either with the naked eye or by utilizing a GG420 Longpass filter either in goggle or camera filter format (in the Crime-lite Auto, the GG420 Longpass is labelled as ‘VIS’).

This small collaborative study provides supporting evidence that the Crime-lite 82S UV, the Crime-lite Auto and the Crime-lite ML-Pro all provide a suitable UV light source (365nm) which can be utilized in conjunction with Spermtracker technology.

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