Non-destructive identification of forensically relevant body fluid stains using a portable electronic nose: A pilot study

Abstract

Identification of bodily fluid stains is crucial for forensic investigations. While current molecular detection methods provide high accuracy, their destructive sampling nature imposes significant limitations on trace samples by compromising sample integrity and subsequent short tandem repeat (STR) profiling. To date, no non-destructive method for fluid identification has been reported. This study introduces a novel portable electronic nose (e-nose) technology that facilitates non-invasive differentiation through the detection of volatile organic compounds (VOCs) in bodily fluids. Requiring only 3–4 min per test while preserving DNA integrity, this approach effectively distinguishes morphologically similar fluids such as blood and menstrual blood, offering an innovative solution for the non-destructive analysis of forensic body fluid. In this study, VOCs from 200 body fluid samples—including blood, saliva, semen, vaginal secretions (VS), and menstrual blood (MB)—were analyzed using electronic nose technology. Samples were collected via sterile swabs (n = 100) and toilet paper (n = 75). Radar plots indicated that sensor S7 (W1W) exhibited peak responses across both carriers. Linear discriminant analysis of the 175 samples revealed distinct clustering patterns (ANOSIM R = 0.088, p < 0.001). The random forest-based predictive models demonstrated that the general model—non-carrier-specific with n = 175—achieved accuracies of 100.00 % for VS, 90.91 % for blood, 81.82 % for semen, 72.73 % for MB, and 63.64 % for saliva; resulting in an overall accuracy of 81.82 %. Notably, when specifically utilizing toilet paper as a carrier, accuracy improved to 92.00 %, with saliva, MB, and VS achieving perfect scores at 100.00 %, while blood and semen reached accuracies of 80.00 %. An external validation set comprising n = 25 was employed to assess accuracy using sterile swab carriers; results indicated an overall accuracy rate of 84.00 %. Specifically: both blood and saliva achieved perfect scores at 100.00 %, whereas semen and MB recorded accuracies of 80.00 %. Conversely, the lowest accuracy was observed for VS at 60.00 %. This study marks the first use of a portable e-nose to differentiate common body fluids, offering a promising, low-cost, non-destructive and user-friendly approach for forensic analysis.