Electrochromic Detection of Latent Fingermarks on Metal Surface Using 1,1′‐Dibenzyl‐4,4′‐bipyridinium Dichloride

The electrochromic detection of latent fingermarks on polished or unpolished, flat or curved metal surfaces is described using electrochromic material, 1,1’‐dibenzyl‐4,4’‐bipyridinium dichloride. The surface area covered by fingermarks acts as an insulating mask, causing 1,1’‐dibenzyl‐4,4’‐bipyridinium dichloride to change color and produce inversed images of the fingermark. By changing the applied potential, the optical properties of 1,1’‐dibenzyl‐4,4’‐bipyridinium dichloride can be continuously and reversibly adjusted to optimize the visual contrast of fingermarks, so as to realize the detection of latent fingermarks on stainless steel surface. It is demonstrated that the fabricated electrochromic devices can detect the fingermarks on these types of surfaces within twenty seconds at −1.0∼−2.0 V. This work can qualify as a tangible improvement in fingermark detection of the natural fingermarks on the never‐cleaned (more than 3 years) and curved surfaces of daily‐used container, e. g. cup, and the handle of cleaning tool, mop.