Raman spectroscopic signature of semen and its potential application to forensic body fluid identification.

A great potential of Raman spectroscopy for non-destructive, confirmatory identification of body fluids at the crime scene has been reported recently (Virkler and Lednev, Forensic Sci. Int. 2008). However, that analysis was carried out on only one sample of each body fluid and did not take into account any variations that might occur between different donors of the same fluid. This paper reports on the role of heterogeneity within a sample as well as among multiple donors for human semen. Near-infrared (NIR) Raman spectroscopy was used to measure spectra of pure dried human semen samples from multiple donors in a controlled laboratory environment. The major chemical components that contributed to the Raman spectrum of semen were determined and used to tentatively identify the principal spectral components. The issue of potential spectral variations that could arise between different donors of semen was also addressed. Advanced statistical analysis of spectra obtained from multiple spots on dry samples showed that dry semen is heterogeneous and its Raman spectra could be presented as a linear combination of a fluorescent background and three spectral components. The relative contribution of each of the three components varies with donor, so no single spectrum could effectively represent an experimental Raman spectrum of dry semen in a quantitative way. The combination of the three spectral components could be considered to be a spectroscopic signature for semen. This proof-of-concept approach shows the potential for Raman spectroscopy to identify an unknown substance to be semen during forensic analysis.