Enhancing the visualization of latent fingerprints by electrochemiluminescence of rubrene

We report how electrochemiluminescence (ECL) of rubrene can be utilized for enhancing the visualization of latent fingerprints in two different modes. The enhancement arises from the spatially selective ECL generation either from the substrate surface uncovered by the fingerprint or the fingerprint itself, designated negative or positive imaging mode, respectively. The negative mode is performed directly in an electrolyte solution containing rubrene and co-reactant. Given that organic residues in the fingerprint deposit make the underlying surface electrochemically inert or less active, ECL reaction occurs only on the surface untouched by the fingertip, generating a negative impression with a dark ridge pattern against the illuminated background. The positive imaging mode is based on the preferential adsorption of rubrene aggregates to the ridge materials via physical attraction; then the fingerprint can glow via ECL reaction in a solution containing co-reactant under an appropriate applied potential.