Phenotype profiling for forensic purposes: Nondestructive potentially on scene attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy of bloodstains

Phenotype profiling is one of the most important analyses during a forensic investigation. Current methods of phenotype profiling based on the analysis of body fluid traces are destructive to the sample and need to be performed in a lab. In this study, attenuated total reflection Fourier transform-infrared (ATR FT-IR) spectroscopy was evaluated as a potentially nondestructive, rapid, and in situ method for phenotype profiling based on the analysis of biological stains. Specifically, ATR FT-IR spectroscopy was used for discriminating sex and race based on the analysis of bloodstains. It is known from the literature that the biochemical composition of blood changes with donor sex and race. ATR FT-IR spectra were acquired from dry bloodstains. Partial least squares discriminant analysis (PLSDA) was used to enhance the capability of our method by creating models to classify Caucasian, African American, and Hispanic donors according to their sex and race. This approach was evaluated by subject-wise leave-one-out cross-validation, resulting in over 90% correct classification. In addition, the main models were validated externally with four hold-out samples, which were not used for the training data set. The validation with hold-out samples resulted in 92% accuracy for both sex and race predictions based on individual spectra. Most importantly, 100% accuracy for both sex and race predictions was found at the donor level since more than 50% spectra were correctly classified for each individual donor. Overall, this proof-of-concept study demonstrated the great potential of ATR FT-IR spectroscopy for phenotype profiling for forensic purposes based on dry bloodstains.