Latent fingerprint enhancement by Ag nanoparticle electrodeposition on metal surfaces

Fingerprints are central to criminal investigations as the most common physical evidence for identification of an individual. However, visualising latent (non-visible) fingerprints is a challenge, particularly on metallic surfaces. In this work, silver nanoparticles (AgNPs) were electrodeposited on fingermarked metal surfaces (stainless steel, copper, brass) by reduction of silver ions in aqueous AgNO3/KNO3 under potentiostatic control. The effectiveness of this methodology and the quality of the developed fingermark images were assessed by scanning electron microscopy, the UK Home Office grading system, automated forensic analysis software and a novel quantitative contrast evaluation methodology. The images clearly permit identification of the ridge patterns and minutiae of the fingermark, even for aged samples and metallic substrates with complex background colour and/or texture, typified by keys and coins. On the basis of the data presented, we propose that this methodology is useful for latent fingermark development on diverse metals, producing high fidelity images of quantifiable contrast.