A mass spectrometry technique developed two decades ago has shown promise in addressing a common forensic issue—analyzing overlapping fingerprints.

Crime scenes are often chaotic, leading to the collection of overlapping and weak fingerprints rather than perfectly distinct patterns. Traditional photography methods fall short when it comes to separating these overlapping prints, rendering them almost useless as evidence. However, a recent study from Aarhus University demonstrates that desorption electrospray ionization mass spectrometry (DESI-MS) can successfully analyze overlapping and weak fingerprints lifted with gelatin lifters, offering a potential breakthrough in cases where current methods are ineffective.

“We are presenting a method that has the potential to be integrated into the police’s traditional workflow. If this happens, more fingerprints from crime scenes could be used and evaluated both visually and chemically,” says Kim Frisch, postdoctoral researcher and lead author of the study.

Gelatin Lifters and DESI-MS

Gelatin lifters, commonly used to collect fingerprints from delicate surfaces and irregular objects, are ideal for lifting prints from materials such as peeling paint and door handles. DESI-MS analyzes the chemical compounds in these fingerprints based on their mass by spraying a fine mist of solvent, consisting of electrically charged methanol droplets, onto the surface of the gelatin lifter. This process ionizes substances present in the fingerprint, which are then measured by their mass.

DESI-MS was initially developed for surface analysis in 2004 and was shown in 2008 to be effective in chemically imaging fingerprints on glass and tape. Now, researchers have demonstrated that this method can also analyze fingerprints collected on gelatin lifters, which are widely used by law enforcement agencies. According to Frisch, this is an example of analytical chemistry being adapted for forensic applications with great potential.

Frisch and her team tested the method on laboratory fingerprints before moving on to real crime scene prints provided by the National Special Crime Unit of the Danish Police, with those efforts still ongoing.

More Than a Pattern

The study also aims to utilize chemical imaging for profiling purposes. Fingerprints can reveal much more than just a unique pattern, including clues about drug use, nicotine, caffeine consumption, and even traces of substances like lubricant from condoms. Researchers worldwide are developing ways to use fingerprints to gather additional information, such as gender, age, and lifestyle of individuals.

Frisch’s team at Aarhus University is continuing their 2.5-year study, supported by the Danish Victims Fund, to maximize the data that can be extracted from fingerprints.

While the new method shows significant potential, its practicality may be limited to specific situations due to the time-consuming nature of the scanning process. “We would not be able to analyze samples in the hundreds, as we do with blood samples. We expect that the method will be used in the future as a special analysis in more serious cases, such as murder and rape,” said Frisch.