Save your luminol – new CSI camera detects bloodstains
By Ben Coxworth
November 14, 2010
Watch even one episode of the various CSI shows or any of its imitators, and you’re likely to see a crime scene investigator whip out their bottle of luminol. The chemical product is commonly used for detecting invisible residual blood, as it glows when combined with an oxidizing agent and exposed to the iron in hemoglobin. It does, however, have some drawbacks – luminol is potentially toxic, it sometimes dilutes blood evidence to the point that DNA can’t be detected, it can smear blood spatter patterns, and it sometimes provides false positives. Now, researchers from the University of South Carolina have developed a blood-detecting camera that reportedly does none of those things.
The University of South Carolina camera takes hundreds of pictures of the same area in just a few seconds, using pulses of infrared light.
Various filters are used for some of the photos, blocking out specific reflected wavelengths and allowing selected chemical compounds to stand out from the background. Blood is one of the substances which can be made visible, even in concentrations down to one part in 100 parts water.
In less than two minutes, data from one location can be collected and analyzed.
Other substances which can be detected, and told apart, include household bleach, rust, soda pop, and coffee – these are sometimes mistaken for blood when using luminol. In tests, the camera has been able to detect such substances in four different types of fabric.
Full details of the research are published in the ACS journal Analytical Chemistry.