A new proof-of-concept study that uses a highly sensitive mass spectrometry method to date fingerprints has its authors thinking they can test the promising methods in real criminal cases within the next few years.
In a preliminary new study published in Analytical Chemistry, researchers Paige Hinners, Madison Thomas and Young-Jin Lee from Iowa State University report they can link compounds contained in fingerprints with their age. While crime lab scientists have relied on fingerprints for over a century, pinning down the time the fingerprint was left has proven difficult. Knowing the age of a fingerprint can help investigators establish a better timeline, including ruling out a suspect or contradicting a suspect’s story.
Using prints collected from three donors, the researchers tracked shifting levels of triacylglycerols using matrix-assisted laser/desorption ionization mass spectrometry (MALDI-MS).
“Most compounds in fingerprint can be measured with this technique but we focused on triacylglycerols (body oil) as they are highly abundant and much more reliably measured than others,” Lee told Forensic.
The MALDI-MS results indicated the researchers could reliably determine the triacylglycerol degradation rate for each person over the course of seven days. But the rate differed among individuals, with one person's triacylglycerols declining more gradually than the others. The researchers attribute this difference to higher levels of lipids in that individual's fingerprints. The method also worked on residues that had been dusted with forensic powder.
“Ambient ozonolysis of fingerprint triacylglycerols has been recently shown by others, but it is the first time to show that it can be used to reliably measure the relative change of fingerprint composition over the first few days of deposition,” Lee said.
The MALDI-MS technique is a substantial, practical leap forward as it is sensitive enough to leave the evidence intact. Previous work that relied on gas chromatography-mass spectrometry (GC-MS) of other compounds could only distinguish whether the fingerprint was older than 8 days and was destructive—fingerprints could not be kept as evidence afterward, opening a legal black hole.
In addition to being non-destructive, Lee said MALDI-MS can simultaneously detect other compounds, such as explosives or drugs that the suspect come into contact with. It can also chemically distinguish overlapped fingerprints.
The researchers say that although a large-scale study is needed to better understand how lipid levels affect triacylglycerol degradation, this analysis is a first step toward developing a better fingerprint aging test.
“This publication is still a proof-of-concept experiment, although very promising,” Lee said. “We just got new funding from the forensic program of the National Institute of Justice. We will continue to thoroughly study the fingerprint aging for multiple variables, such as environmental effect, individual differences, and experimental conditions.”
Photo: Levels of an unsaturated triacylglycerol decline in fingerprints from an individual from day 0 (top) to day 1 (middle) and day 3 (bottom). Credit: Adapted from Analytical Chemistry 2020, DOI: 10.1021/acs.analchem.9b04765