Children’s fingerprints disappear faster than those of adults — a little-known fact that can hamper investigations of kidnapping cases. To investigate this phenomenon, a team of researchers used beams of infrared light at NSLS as a powerful detective’s microscope, finding that fingerprint staying power is based on the amount and types of oil in your skin.
Forensic scientists often use techniques like magnetic filings dusting, iodine, and cyanoacrylate fuming to see otherwise invisible, or latent, fingerprints. Although efficient, inexpensive, and relatively fast, these methods make it difficult to preserve trace evidence found in a fingerprint.
Previous research has linked the difference in the longevity of fingerprints to the type of oil found in a person’s skin. This oil, known as sebum, is just one of the components of a fingerprint, which also can contain small pieces of skin and sweat residue. The NSLS researchers wanted to determine how these fingerprint components change over time in adults and children.
Using a collection of latent fingerprints given by father and son pairs, the researchers watched for chemical changes over the course of four weeks. Twice a week, one fingerprint from each participant was dusted, lifted, and analyzed based on the number of features, or minutiae, visible. At the same time, a non-invasive synchrotron technique called Fourier transform infrared microspectroscopy (FTIRM) mapped the location and makeup of the skin and sebum in the prints.
At all points in time, the fathers’ prints dusted darker than those from their sons, remaining virtually unchanged during the study, while the fine minutiae of their children became increasingly more difficult to see.
As predicted by previous studies, FTIRM showed that adults produce more sebum than children, which leads to darker prints. Researchers also found that the composition of the lipids, or fats, in sebum differ significantly between adults and children.
Adult sebum has higher concentrations of stable lipids such as squalene and wax esters, which are less likely to vaporize over time. Conversely, the sebum of children contains higher levels of cholesterol and branched chain free fatty acids — unstable lipids that break down more quickly.
The results could pave the path toward more advanced fingerprint detection techniques.
K.M. Antoine, S. Mortazavi, A.D. Miller, L.M. Miller, “Chemical Differences are Observed in Children’s Versus Adults’ Latent Fingerprints as a Function of Time,” J. Forensic Sci., 55(2), 513 (2010).
Top: FTIRM images generated from a child’s fingerprint, showing the a) protein
in the fingerprint, and b) the oil (sebum) in the print.
Bottom: Lead author Kimone Antoine