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Analytical Chemistry

Determining The Age Of Fingerprints

Forensic Science: New technique could help investigators validate and prioritize evidence

by Andrea Widener
August 31, 2015 | A version of this story appeared in Volume 93, Issue 34

Credit: Muramoto/NIST
Palmitic acid (green) migrates over three days from a fingerprint’s peaks to its valleys.
Chemical imaging of a fingerprint shows the relative distribution of palmitic acid (green) and the more immobile waxy residue (red) when freshly deposited (left) and after 72 hours (right), showing the migration of palmitic acid.
Credit: Muramoto/NIST
Palmitic acid (green) migrates over three days from a fingerprint’s peaks to its valleys.

A fingerprint’s distinct ridges and swirls gradually erode and become fuzzy as its chemical constituents migrate from peaks to valleys. Now, chemists at the National Institute of Standards & Technology say that how quickly those ridges fade could be used to determine how long a fingerprint has been on a surface.

That information is important for forensic scientists seeking to know which fingerprint was left near the time of a crime. “You’re trying to sort out the fingerprint that matters,” explains Suzanne Bell, a chemist who studies forensic techniques at West Virginia University and was not involved in the NIST work.

A person depositing a fingerprint leaves behind thousands of chemicals on a surface. Forensic scientists have been hoping to mine them for information as varied as the donor’s age or sex or what substances that person might have touched, such as explosives or drugs.

The NIST researchers, Shin Muramoto and Edward Sisco, were originally searching for trace amounts of drugs in fingerprints when they noticed that some of the deposited chemicals were moving from the fingerprints’ peaks to the fingerprints’ valleys over time. That observation prompted them to turn their research technique—time-of-flight secondary ion mass spectrometry (TOF-SIMS)—toward the question of the age of fingerprints, Muramoto says (Anal. Chem. 2015, DOI: 10.1021/acs.analchem.5b02018).

The researchers narrowed their focus to the migration over time of fatty acids, such as palmitic acid. These substances are small enough to ionize with TOF-SIMS, Muramoto explains, and they are easy to identify.

By examining the migration of palmitic acid, the NIST scientists were able to predict the age of a fingerprint. The paper focuses on the first four days after a fingerprint was left. Muramoto says researchers have since been able to predict the age over several months.

The test is not fit for the field yet—the 3- by 3-foot instrument is firmly ensconced in the lab—but Bell thinks it is a good first step toward finding a way to determine the age of fingerprints perhaps when used with other techniques. “I certainly think it could become a tool in the toolbox,” she says.



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