You’d normally think of fingerprints as just a means of identifying criminals. Important as that is, the marks also contain a wealth of chemical residues which could give access to the sort of clues that would make Inspector Lestrade salivate.

Sherlock Holmes famously used his microscope to find traces of glue in the rim of a hat found at a crime, then used the information to deduce that a a picture-maker he already suspected was probably the culprit. Fast forward to forensics in 2011, and scientists are using the same principles, but now it’s possible to measure chemical residues in substantially smaller items than hats.

MALDI mass spectrometry is a key analytical tool for identiying chemical traces, but using an instrument like a MALDI-MS in the field is difficult. Creating the right matrix material to hold the sample is usually the most difficult part of conducting a MALDI experiment, and making the matrix outside of a laboratory environment is especially tricky. But Simona Francese and her coworkers at Sheffield Hallam University have recently published a paper which details a new type of matrix. The great thing about it is its simplicity – to visualise and prepare a fingermark for MALDI analysis, powdered α-cyano-4-hydroxycinnamic acid (α-CHCA) is dusted onto the mark. This powder can be directly substituted for the innocuous powders usually used for dusting, so when a fingerprint is identified, the first step of preparation for MALDI analysis is already done.

a-cyano-4-hydroxycinnamic acid

α-cyano-4-hydroxy cinnamic acid

At this stage the print is visible, so it can be optically photographed and used to identify the owner. All that’s then required is a spray of dilute acid solution and a bit of time for the matrix to dry. The print-shaped matrix can then be lifted off with double-sided carbon tape and transferred to a MALDI plate for analysis.

α-CHCA is the first MALDI matrix material that can be legitimately used as dusting medium on a range of surfaces; other  matrices (mainly silica and carbon based media) have been shown to work only on aluminium surfaces. If the fingerprint is on a plastic cup, say, or a piece of varnished wood, only α-CHCA has been shown to work.  α-CHCA is also fluorescent, so it can also be viewed under a powerful fluorescence microscope, providing extremely high magnification images of the details of the print. Some matrices ‘hold on’ to certain types of chemical species – amino acids, notably – better than others, but the researchers have shown that this matrix doesn’t have those problems.

The MALDI analysis will then be able to identify chemicals which the fingermark owner has been in contact with and should help solve crimes.  The technique is so simple and easy to use that the UK Home Office announced a few days ago that it was awarding £80,000 to Sheffield Hallam’s Biomedical Research Centre (BMRC) so that they can further develop this work.

Josh Howgego

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