Aging analysis of latent fingerprint residues by tracking carotenoid and lipid degradation by Raman spectroscopy

Fingermarks have been crucial in forensic investigations for centuries, aiding in both individual identification and crime scene reconstruction. However, a reliable method for dating fingerprints found at crime scenes remains elusive. This study explores the use of Raman spectroscopy to analyze the chemical composition of latent fingermarks residues and track changes over time, specifically within 90 days of deposition. Fingermarks from three male donors were collected and aged under controlled conditions. Raman spectra revealed several chemical markers, with carotenoids showing a significantly faster degradation rate than lipids, following first-order kinetics and varying among donors. Both carotenoids and lipids underwent molecular changes, with carotenoids shifting from trans to cis-isomers, and lipids from cis to trans. These transformations led to oxidation processes and the generation of by-products. Lipid degradation showed a gradual decrease in unsaturated bonds during the first 40 days, followed by a more rapid decline. Raman data also indicated continuous lipid hydrolysis over time. The study provides insights into the chemical aging of fingermarks and suggests that Raman spectroscopy could become a useful non-destructive method for estimating the age of fingermarks in forensic applications.