Seminal stain fluorescence using three alternate light source-barrier filter combinations on six different colors of cotton fabrics
Su, Joey Young
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Detecting and locating semen stains is crucial when creating a linkage between the offender and items of evidence. Currently, the two most common methods of semen stain detection used in crime scenes and items recovered from crime scenes are fluorescence and chemical examinations. An alternate light source (ALS), which causes semen to fluoresce under different wavelengths, is an established technique that utilizes converted light for the detection of latent stains. The other method relies on chemically identifying the presence of acid phosphatase activity in semen. Previous studies have concluded that semen optimally fluoresces at 450 nm wavelength with an orange barrier filter. In this paper, the fluorescence of seminal stains under different laboratory conditions is compared in order to investigate the significant factors that may affect semen detection. The variables investigated in this paper include six colors of plain cotton fabrics, three excitation spectra, three semen donors, five semen concentrations and six fabric textures. The intensity of the fluorescence was calculated using the image processing program ImageJ. ImageJ contains a color channel split function that allows photographs to split into 8-bit grayscale images containing the red, green and blue components of the original photographs. Each color channel was individually compared to each other and to the original RGB photographs to determine whether color channel splitting has an effect on the detectability of seminal stain fluorescence. This study suggests that the most significant factor that affects the detectability of a semen stain, aside from the concentration of the stain, is the color of the substrate. The texture of the substrate had no significant effect on the fluorescence and no significant variation in the semen stain fluorescence was observed from the three donors tested; however, future studies are necessary to confirm these findings. Forensic analysts should consider the background color when selecting the excitation light wavelength, and may need to utilize an alternate approach such as a chemical mapping examination, particularly for locating diluted semen stains on a dark background.