Label -free physical and electrochemical imaging of latent fingerprints by water and SECM

A label-free method that can doubly image both the physical patterns and the electrochemical information of latent fingerprints (LFPs) on nitrocellulose (NC) membrane has been achieved here by water and scanning electrochemical microscopy (SECM). In this approach, the NC membrane with LFP (LFP/NC) sample was first placed in water, where the different absorption of water onto relatively hydrophobic ridge residues of LFP versus NC membrane background resulted in a high-resolution physical ridge pattern of the fingerprint to naked eyes within just 1–3 s and could further be photographed by a digital camera. Thereafter, the LFP/NC sample was electrochemically imaged by recording the current variations of SECM tip scanning over the label-free fingerprint in the surface-interrogation (SI) mode. The methyl viologen (MV2+) was chosen as the redox mediator to react selectively with the electroactive species in the fingerprint ridge residues rather than furrow regions, which could cause the sharp contrast of the SECM tip current for imaging. Both the collected physical and electrochemical images of LFPs can provide high resolution up to level 2 and level 3 features required for personal identification. In addition, for the first time commercial NC membrane instead of adhesive forensic tape was discovered here for lifting the LFPs from various surfaces, which can then be imaged by this electrochemical approach. Taken together, this method demonstrates a powerful strategy for directly imaging the electrochemical information in LFPs without damaging the fingerprint physical ridge pattern on various substrates, so it has great potentiality in individual identity related applications. © 2020 Elsevier Ltd