Feasibility of a handheld near infrared device for the qualitative analysis of bloodstains

Abstract

One of the most common tasks in criminal investigation is to determine from which tissue source a biological fluid stain originates. As a result, there are many tests that are frequently used to determine if a stain is blood, semen or saliva by exploiting the properties of certain molecules present within the fluids themselves. These include chemical reagents such as the Kastle-Meyer or Acid Phosphatase tests, as well as other techniques like the use of alternative light sources. However, most of the tests currently available have some major drawbacks. In this study, a handheld near-infrared spectrometer is investigated for the specific identification of deposited bloodstains. First, a calibration was carried out by scanning over 500 positive (blood present) and negative (blood absent) samples to train several predictive models based on machine learning principles. These models were then tested on over 100 new positive and negative samples to evaluate their performance. All models tested were able to correctly classify deposited stains as blood in at least 81% of tested samples, with some models allowing for even higher classification accuracy at over 94%. This suggests that handheld near infrared devices could offer great opportunity for the rapid, low cost and non-destructive screening of body fluids at scenes of crime.

Principles and Applications of Miniaturized Near‐Infrared (NIR) Spectrometers

“…Interestingly, it was shown recently that miniaturized NIR spectroscopy was capable of analyzing blood stains, [97, 98] and that the sensitivity of the method did not seem to present a major issue. This shows the potential for NIR spectroscopy to compete with IR or Raman techniques, which are already in use for such purposes [99–102] …”

Vibrational Spectroscopy and Chemometrics in Forensic Chemistry: Critical Review, Current Trends and Challenges

“…Two studies 213,214 have used portable NIR spectrometers and supervised pattern recognition methods for discrimination and confirmatory identification of bloodstains in different substrates. In the first, Pereira et al 213 analyzed dried human and animal bloodstains and several red-colored products that could be commonly perceived as blood, such as red lipstick, pepper sauce, soy sauce, red wine and balsamic vinegar.…”

“…PLS-DA correctly classified human blood and other stains in all substrates. Morillas et al 214 analyzed bloodstains and eight other substances that resembled fresh or dry blood, such as red wine, red ink, tomato sauce, fake blood, coffee, red food coloring, red paint and beet root juice. The substrates used were glass slides, tile, wood, 100% leather, 100% acrylic and 100% cotton.…”

Hyperspectral Imaging for Bloodstain Identification

“…Morillas et al used a portable NIR spectrometer for bloodstain identification. The authors observed good results with 81–94% accuracy with different classification models [ 22 ].…”