Science

Forensic scientists gather steam in creating an alternative to luminol

Forensic scientists gather ste...
A hand steamer and an infrared camera are used to reveal blood markings on a black background
A hand steamer and an infrared camera are used to reveal blood markings on a black background
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A hand steamer and an infrared camera are used to reveal blood markings on a black background
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A hand steamer and an infrared camera are used to reveal blood markings on a black background

If you've watched any of the various CSI TV shows, then you'll already be familiar with luminol. It's a chemical that, when sprayed onto trace amounts of blood that aren't visible to the naked eye, causes that blood to glow a pale blue. Unfortunately, however, the application of luminol and its reagent chemically compromises the crime scene, plus the glow can't be seen outdoors in sunlight. That's why scientists at the University of South Carolina are exploring the use of an innocuous alternative substance … steam.

Developed by a team led by chemistry professors Michael Myrick and Stephen Morgan, the "steam thermography" technique involves first using a hand-held steamer to heat up surfaces being investigated. Forensic investigators then view that surface through what is essentially a pair of night-vision goggles.

Ordinarily, such infrared goggles work by highlighting differences in the amount of heat radiation given off by objects – both animate and inanimate. In this case, however, the goggles are also able to highlight differences in the chemical composition of surfaces, based on the fashion in which their molecules emit heat.

As a result, droplets of blood diluted as low as 1/1,000 still "pop out" in real time when viewed through the eyewear, even outdoors in bright sunlight.

The heating process has been found not to affect DNA testing of the blood, plus the steam thermography process isn't fooled by bleach, rust or coffee stains – all of which can be misread as blood by luminol.

A paper on the project was recently published in the journal Analyst. The project builds on research that began several years ago.

Source: University of South Carolina

2 comments
esar
I wonder why it has to be steam, wouldn't a hair dryer do the same thing?
Sleepychemist
Infrared cameras see one thing: the summary of wavelengths in their detectable region. Heat (or mid infrared region) is observed through this type of infrared camera. Simply blowing air on the fabric yields no selectivity. The heat capacity of the fabric(with and without dilute blood) heats the area. When steam is applied, a hydrophobic/hydrophilic interaction happens. Any coating on a surface will interact with the water vapor differently than the fabric or a different coating: remember oil and water, this is practicing the same idea but in the gas phase. Blood is filled with proteins which are much more hydrophilic than the fabric. The adsorption of water onto the surface heats the fabric: more water, more heat of adsorption. Hot air has the same RH as the room (maybe a little more).