Latent fingermarks on copperplate paper: facile visualization via electrochromism of 1,1′-bis(3-sulfonatopropyl) viologen

Visualization of latent fingermarks has ever been realized through electrochromism (EC) on stainless steel used as an electrode of electrochromic device (ECD). However, enhancement of fingermarks on paper using EC remains unresolved. Considering the hydrophobicity differences between the protruding and the concave parts of sebum-containing fingermarks, we attempt to devise ECDs capable of visualizing latent fingermarks on copperplate paper. It is demonstrated that the sulfonated viologen, 1,1′-bis(3-sulfonatopropyl) viologen can be used as an excellent chromophore for latent fingermarks enhancement on copperplate paper using EC, with either 1,1′-ferrocenedimethanol, or vitamin C or potassium ferrocyanide/potassium ferricyanide as the electron mediator. The as-fabricated ECDs can display the characteristic second level details of latent fingermarks left on copperplate paper under a voltage of -1.2 V. This work opens a new avenue for visualizing latent fingermarks on copperplate paper, which is a frequently-used potential physical evidence in office and daily life that may be useful for forensics.