Non-destructive enhancement of latent fingerprints on stainless steel surfaces by electrochemiluminescence

Visualization and detection of latent fingerprints (LFPs) on metal surfaces are of highly practical importance, e.g., in identifying gun cartridges. We report herein the visualization of LFPs on stainless steel surfaces by electrochemiluminescence (ECL). Since organic residues, such as fatty acids, in the fingerprint deposit make the underlying surface electrochemically inert or less active, an ECL reaction occurs only on the metal portions untouched by the fingertip, hence generating a negative image of the fingerprint. The popular ECL reaction solution, consisting of ruthenium(II) tris(2,2'-bipyridyl) and tri-n-propylamine, was used for this imaging purpose. Factors, including the applied potential and the concentration of ECL luminophore, as well as the stability of ECL negative images, were investigated to achieve a satisfactory visualization enhancement. This imaging approach is simple, rapid, non-invasive, and no pre-treatment either on the background or on the fingerprint itself is needed. It constitutes a powerful tool for visualizing LFPs on metal surfaces. This method was also demonstrated to be suitable for enhancing LFPs collected from various surfaces.