To catch a thief...use MALDI-MSI

Caren B. Les, caren.les@photonics.com

Fingerprints can be highly incriminating, and they will become even more so, thanks to a technique that could help crime-scene investigators glean extra clues about suspects – from information about recently ingested foods or medications to what time the prints were left.

The new process could help turn matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) into a recognized investigative tool, especially in cases where a suspect’s prints do not positively match prints on file in law enforcement databases.

In MALDI-MSI, a matrix solution is applied to a sample – for example, the gland secretions and skin-surface material that make up fingerprints – then a laser triggers desorption just on the surface of the sample, recording the mass spectrum. The images generated provide information about the amount of material present and its spatial distribution.

A fingerprint is fired with a MALDI-MSI laser with the resulting desorption of the molecules that produce various fingerprint images according to molecular distribution. Courtesy of Biomedical Research Centre, Sheffield Hallam University.

One significant challenge has been that scarcely visible latent fingerprints must be enhanced before MALDI-MSI analysis can be used. The solution has been to use a “dry” matrix, deposited as a powder, or a “wet” matrix, deposited as a droplet spray. The application method directly affects the resolution of the resulting image, and neither has been ideal in the eyes of the scientific community.

A “dry wet” matrix deposition method, in which the matrix is dusted onto a sample and then followed by a solvent spray using a robotic device, enabled scientists at Sheffield Hallam University in the UK to overcome this problem. The method enhances latent prints so that the evidence can be photographed and exposed to UV light and fluorescence radiation, enabling clearer images.

The scientists found that, with this technique, MALDI-MSI can detect fingerprint components originating both within the suspect’s body and outside of it – things the suspect either consumed or touched – while still enhancing the familiar fingerprint ridge patterns for visual analysis. The technique can be used for fingerprints found on a variety of surfaces, including glass, plastic, wood and metal.

The work was published online in Analytical Chemistry on June 13. The researchers say there is reason to believe it will become a standard tool in police investigations within a few years. “Our goal is to get the technology included in police manuals on how to detect fingermarks at crime scenes,” said Dr. Rosalind Wolstenholme, co-developer of the technique.

The UK’s Home Office Centre for Applied Science and Technology recently co-funded an £80,000 (about $130,000) doctoral fellowship with the center for further testing.