Confirmatory Semen Detection by Combination of Prostate Specific Antigen Detection and Micro-Raman Spectroscopy

Ilan Feine, DIFS, Israel Police, Jerusalem, Israel
Ron Gafny, DIFS, Israel Police, Jerusalem, Israel
Iddo Pinkas, Department Of Chemical Research Support, Weizmann Institute Of Science, Rehovot, Israel

In sexual assault cases, the confirmative forensic identification of semen as the source of male DNA found on the victim’s body or clothing, is crucial for investigators as well as for the court. The most acceptable and reliable means for semen identification is the microscopic detection of sperm cells, since they are not found in other body fluids or secretions. However, technical or physiological obstacles may cause the demonstration of morphologically intact spermatozoa extremely challenging. Detecting prostate specific antigen (PSA) in a questioned body fluid stain or other sexual assault casework items strongly indicates the presence of semen and is particularly useful when no sperm cells are observed. Yet, it has several false-positives which may prevent confirmative semen classification. Namely, the presence of PSA and nucleated cells in male urine could lead a forensic examiner to an incorrect body fluid conclusion. Micro Raman spectroscopy is a molecular spectroscopy based on the inelastic light scattering of monochromatic light and its potential to detect a wide range of body fluids has been demonstrated in recent years. In the present study, we show how the combination of PSA tests and micro Raman spectroscopy offers a simple, non-destructive and quick method for confirmatory semen detection. After positive PSA tests, micro Raman spectroscopy can easily corroborate semen presence and exclude the possibility of urine false positive detection. The sensitivity of this practice was demonstrated by measuring micro Raman spectra of diluted urine and semen (up to 1%), as well as their spectra after extraction from cloth and swabs. These results show the advantages of combining micro Raman spectroscopy and PSA tests when examining sexual assault casework items.