Revelação de impressão digital latente em superfície metálica a partir da eletrodeposição do polipirrol dopado com alaranjado de metila e índigo carmim

Abstract

Forensic experts seek through representations of fingerprints (palm and sole) found at a crime scene to help justice in the elucidation of cases. This study presents a new approach to deal with the challenge of detecting latent fingerprints on metallic surfaces. The proposal consists of using the technique of electrodeposition of conjugated polymers as a central methodology. Polypyrrole doped with methyl orange and indigo carmine dyes was used to reveal fingerprints on a stainless steel surface. In this method, the natural sebaceous deposit of fingerprints is used, which acts as an isolation mask. This allows the electrochemical deposition processes to be directed only to the grease-free areas on the metallic surface, that is, in the regions between the ridges of the fingerprint residue. Polypyrrole was electrodeposited by oxidizing the monomer in a dye/H2O solution using potentiodynamic, galvanostatic and potentiostatic methods. The results show that AM and IC doped polypyrrole films, which were developed via chronoamperometry, showed excellent contrast between the fingerprint and the steel plate. However, during the fingerprint aging analysis, it was observed that there were failures in the polymer deposition in a large part of the fingerprint. The chronopotentiometric method demonstrated superior efficiency. The developed fingerprints did not show flaws in the polymer deposition, even after 30 days of aging. This method was classified as efficient and reproducible. The quality of the developed fingerprint was evaluated using scale uk home office, with 74% and 90% of impressions graded 3 and 4 (strong and very strong) using the chronoamperometry and chronopotentiometry methods, respectively.