Using ATR-FTIR spectroscopy and machine learning for forensic hair identification

The purpose of this experiment is to utilize attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy for the discrimination of different types of hair, as numerous studies have substantiated its efficacy in substance classification. In this study, ATR-FTIR spectroscopy was employed to analyze scalp hair, pubic hair, and armpit hair from human subjects. Additionally, a machine learning model was integrated to differentiate between hairs originating from distinct body regions. Because of the limited sampling conditions, we only chose samples from Chinese people who have been living in Shanghai and the surrounding areas for a long time to conduct the experiment. We developed partial least squares discriminant analysis (PLS-DA), random forest (RF), and support vector machine (SVM) classification models and compared their performance in identification. The results show that the SVM model has the best identification results with 90.37% accuracy, 90.37% recall, and 90.38% precision. This preliminary study suggests that ATR-FTIR spectroscopy combined with SVM may be an effective and promising aid in assisting the identification of hair in different parts of the human body. This method is non-destructive, fast, and accurate, and does not require a sample preparation process, which makes it promising in the field of forensic science. Also, we found that the main substance differences that contributed to the good distinction between hairs were expressed in amide I, followed by amide III and C-H deformation.