Inovação em biometria forense: polímeros condutores aplicados na revelação de impressões digitais latentes

Abstract

Fingerprints have a key role in criminal investigations as one of the most used physical traces in identifying criminals. To face the challenge of developing latent fingerprints on metal surfaces, this work brings a new proposal for a methodology based on the electrodeposition of conducting polymers. Poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (2,2':5',2'' - terthiophene) (PTT) polymers were used for developing latent fingerprints on stainless steel and brass cartridge cases. The technique exploits the sebaceous deposit of the fingerprint as an isolation mask, so that the electrochemical deposition processes can only act in fat-free areas on the metallic surface, that is, between the ridges of the fingerprint residue. PEDOT was electrodeposited by oxidation of the monomer in LiClO4/H2O solution using potentiodynamic, potentiostatic and galvanostatic deposition methods. The results indicate that the amount of PEDOT in the range of 1.2 ≤ Г ≤ 4.1 μmol cm-2 electrodeposited in the studied samples is an efficient methodology to reveal latent fingerprints, even after 30 days in which the sebaceous residues were left on the surface. PTT was electrochemically deposited by chronoamperometry using a 2.2':5',2"-terthiophene (TT) (C4H9)4NBF4 / CH3CN solution on the PEDOT film, in stainless steel, producing a bilayer. The fluorescent properties of bilayer can be applied in Forensic Papilloscopy to develop fingerprints on metal surfaces under UV light. An oxidation process of the metal surface occurs simultaneously with the electrodeposition of the polymer, further improving the contrast between the fingerprint and the cartridge case. The quality of the development of fingerprints was evaluated by the Griaule Forensic Fingerprint® software and confirmed using the Bandey scale, with 87% and 14% fingerprints with grade 4 (very strong development) in stainless steel and cartridge cases, respectively, and 84% and 57% with grade 3 (strong development) in stainless steel (PEDOT+PTT) and cartridge cases (PEDOT), respectively.