Sweat inspiration

Sweat could provide police with clues to a criminal’s identity, claim researchers at California’s Lawrence Berkeley National Laboratory.

When a person touches an object, salts, proteins and fatty acids from the surface of their skin are left behind, even if the touch is not sufficient to leave a clearfingerprint.

According to the Berkeley team, infrared light can be used to analyse what it believes are the unique traces left by an individual when his or her skin comes into contact with any surface. The technology could eventually be developed to help investigators and forensic scientists solve crimes.

Researchers conducted experiments using the centre’s Advanced Light Source, an electron synchrotron that produces intense beams of photons in the IR spectrum. By applying the IR beam to surfaces, it was found that even minute traces of the chemical residues could be identified for analysis.

‘The combination of IR spectroscopy and microscopy is an extremely powerful analytical technique,’ said Dale Perry, a Berkeley Laboratory chemist working with the IR team. ‘In the light of what we have already demonstrated, usingsynchrotron-based IR spectromicroscopy as a forensic tool has a bright outlook.’

All molecules absorb and emit characteristic frequencies within the infrared spectrum. These can then be used to give precise identification of the type of molecule present.The Berkeley team believes the ratio of chemicals found on the skin may differ between individuals, meaning sweat signatures could be as distinctive as fingerprints.During laboratory trials researchers correctly identified three different subjects by the signatures left in residues of their sweat.

The team is now attempting to discover whether the skin chemicals’ spectra can be singled out when mixed with certain other compounds.

If the chemicals can be observed, further experiments and analysis could potentially reveal information about the age and sex of the person to whom the print belongs, and even when the substance was deposited.

The technique could help with investigations where only smudged or incomplete fingerprints are found at a crime scene, providing insufficient evidence for use in court.

Using the IR system samples less than 10 microns across can be successfully analysed. This allowed the team to work with a sweat print measuring less than the size of a single ridge in a fingerprint.

The technique is also non-destructive and does not change the properties of the print or the material it sits on. This means that once a profile has been acquired through IR analysis the undamaged sweat print can be subjected to further forensic testing.

The team say IR spectromicroscopy could also be used to trace biological fluids on cloth, identify the manufacturers or suppliers of chemicals, poisons and drugs by the chemical signature of their constituents, and even identify the geographical origins of dust particles.