Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source

ABSTRACT

A possible method to detect body fluids in forensic cases of sexual assault or abuse is by using forensic light sources, which emit certain wavelengths and excite body fluids to fluoresce. However, the success of the visualization of the fluorescence signal can be significantly reduced when unfavorable conditions - especially daylight - are present or used.

We studied the detection of fresh semen (human, boar) and saliva (human) on different and colored types of fabric. The stained samples were stored for 3 and 5 weeks, respectively, and some were additionally washed with detergent at 30°C (86°F). The portable forensic light source Lumatec Superlight 400 which emits wavelengths from 320 nm (UV) to 700 nm (visible light, VIS) and colored goggles and filters were used.

The very high intensity light source detected semen and saliva in darkness and daylight. No difference were found in samples stored 3 and 5 weeks, respectively. Best results for semen and saliva were obtained using wavelengths between 415-490 nm. For general search for body fluids, excitation of 350-500 nm is preferable. With appropriate goggles (orange (>500 nm) or red (>590)) semen could be detected in 100% and saliva in 60% of the cases. Washing the samples with detergent removed the biological stains in 75% of the cases. The darker the color, the more the fluorescence signal was absorbed. The type of the fabric had however no significant effect on detection of semen and saliva. The recognition rate of saliva was much better than reported for other light sources.

An unexpected observation on the side was that the fluorescence signal of boar semen was clearly weaker than that of human semen, although the amount of sperm cells per ml is 50-150 million for humans and 25-300 million for boar.