Source determination of human and animal oral fluid stains on porous substrates by chemometrics-assisted ATR FTIR spectroscopy: A preliminary study

Oral fluids are common evidence that can be found as stains on a variety of substrates at crime scenes. The porosity of the substrate may influence their collection and analysis. Moreover, companion animals, such as dogs, may appear in many scenarios or even be involved in a crime. Determining the source (identification and classification) of human and canine oral fluid stains on different substrates found at crime scene is important prior to DNA extraction to diminish laboratory cost and time efforts. In the present work, the potential of attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) was explored to study how several types of porous substrates influence in the source determination of human and animal (canine) oral fluid stains. Results showed that the main bands of human or canine oral fluid stains were visible among the characteristic infrared bands of the porous substrates. This allowed the identification of human or animal (canine) oral fluid stains origin in the three types of papers and six fabrics porous substrates studied. Then, the application of Orthogonal Partial Least Square-Discriminant Analysis (OPLS-DA) models to the obtained infrared spectra, allowed the classification of human and canine oral fluid stains independently of the substrate they were deposited on. This approach could be developed for real forensic investigations to distinguish the source (identification and classification) of oral fluid stains as human or animal.