Surface characterization of curcumin-visualized latent fingerprints on metal surfaces.

Visualization of latent fingerprints (LFPs) on metal surfaces using curcumin (CUR) remains a largely underexplored approach. Here, CUR was applied for LFP visualization on brass, steel, Al, and Cu plates and on real-life metal objects (keys, coins, and knives). Fingerprint quality was assessed by stereomicroscopy and characterized in detail using profilometry, SEM/EDS, and vibrational spectroscopy (IR and Raman). Profilometry and SEM/EDS revealed substrate-dependent differences in CUR layer morphology, roughness, and aggregation, indicating that papillary ridge contrast is governed by interactions between fingerprint residues and the underlying surface. Vibrational spectroscopy confirmed the preferential interaction of CUR with lipid-rich LFP components rather than non-specific adsorption on metal substrates and revealed compositional differences in fingerprints deposited on brass and stainless steel. The practical applicability of CUR on real-life metal objects demonstrated that fingerprint persistence and visibility met the legal requirement for forensic usability in the Czech Republic (> 10 minutiae). Overall, these results demonstrate that, under appropriate surface conditions, CUR provides a reliable and environmentally sustainable strategy for targeted LFP visualization on metal substrates.