Chemical Imaging for Compound Identification
Spectroscopy for rapid, contact-free, and non-destructive in situ investigation
Infrared imaging
Infrared imaging has been an emerging technique for a few years now in the field of forensic science. The infrared spectrum presents useful features for detecting and identifying numerous organic and inorganic compounds such as polymers, or for measuring hydrocarbon concentration and moisture content. Moreover, the technique is rapid, contact-free, and non-destructive. This is highly beneficial in applications like the estimation of time of death or the detection of bloodstains on dark backgrounds. Using specific filters, it becomes a powerful tool to detect blood, drugs, fingerprints, and even explosives. It is quite an appealing technology at crime scenes as the investigator can use it in situ and scan the area without coming into contact with any samples, better preserving them, and without having to send the images to a lab for analysis.
Spectral imaging
Nonetheless, infrared imaging represents a serious breakthrough when combined with spectroscopy, commonly known as hyperspectral imaging (HSI). Infrared spectroscopy analyzes the chemical bond within molecules. Searching for characteristic spectral signatures of these bonds allows for the identification of the material under study. HSI does spectroscopy pixel by pixel, identifying compounds in every pixel of an image. It is applicable to any targets that fluoresce or reflect characteristic radiation in this spectral range. It also matches the same advantages of infrared imaging as it works in any kind of environment, requires no sample preparation, and delivers immediate, on-the-spot analysis results.
A new eye at the crime scene
HSI offers significant potential for the detection, visualization, identification, and age estimation of forensic traces. It gives deep insights into what a piece or trace of evidence is made of. For example, it could be used to determine, non-destructively, the nature of a single strand of fibre sampled by a tape-lift. It can also be used to analyze the traces of the chemical binders in dried paint or ink, linking them back to a specific brand or manufacturer. Spectroscopy is a truly versatile tool. Hyperspectral imaging is convenient for use both in a forensic lab or directly at the crime scene.