Electrodeposition of redox materials with potential for enhanced visualisation of latent finger-marks on brass substrates and ammunition casings.
TL;DR
Scientists developed a new way to reveal fingerprints on brass bullet casings using electricity and special chemicals. This method can show incredibly detailed fingerprints - even tiny pores in the skin ridges - and works even after the brass has been heated to 700°C or aged for over 15 months, which could help solve crimes where traditional fingerprint methods fail.
Electrochemical methods can play a key role in the analysis of impression evidence, specifically, latent finger-marks on brass substrates and ammunition casings, the latter being commonly encountered at crime scenes in forensic casework. In adopting such techniques, forensic investigators can potentially overcome some of the challenges associated with traditional visualisation methods, the use of aggressive reagents, preservation of evidence integrity and the need for extensive sample preparation. The spatially selective deposition of conducting/redox active polymers for visualising latent finger-marks on typically low-yield brass ammunition casings is examined here, exploiting the electrodeposition of 3,4-ethylenedioxythiophene (EDOT), together with a first-time study of phenozine vs. phenothiazine monomers, and their combinations at sheet and cartridge brass. Fine tuning of electrochemical protocols and conditions together with optimised monomer feedstocks played a key role in the finger-mark visualisation quality achieved with insights into brass electrochemistry. EDOT-thionine emerged consistently as the most effective combination upon electrochemical deposition on brass sheets, revealing latent finger-marks (groomed) at the highest level of detail (level 3), including pores within the papillary ridges, using a low energy, rapid ( t = 120 s) constant potential ( E app = 0.1 V vs Ag|AgCl) approach. Successful visualisation of groomed and natural (donor) latent finger-marks was achieved following exposure of brass to temperatures of 700 °C and > 15-month room temperature aging. Bespoke electrochemical cells designed to facilitate the use of ammunition casings as working electrodes produced excellent results via potential sweeping, resulting in pristine visualised latent finger-marks (groomed) of grade 3 quality with visible level 3 (> 50 %) features. • Potentiostatic and potentiodynamic approaches to visualisation of latent finger-marks in forensic biometrics. • Phenothiazine/PEDOT electrodeposition on brass ammunition casings with inherent sample retention capability. • Pilot study for groomed and natural finger-mark visualisation on brass following thermal and aging processes. • New methodology based on a non-hazardous, green and low energy approach.
- 1The EDOT-thionine chemical combination consistently produced the highest quality fingerprint visualization on brass, revealing level 3 details including individual pores within skin ridges
- 2The electrochemical method successfully revealed fingerprints on brass even after extreme conditions - heating to 700°C and aging for over 15 months at room temperature
- 3Custom-designed electrochemical cells allowed ammunition casings to be used directly as electrodes, producing grade 3 quality fingerprints with over 50% of the finest detail features visible
- 4The process is rapid (120 seconds), low-energy, and uses non-hazardous chemicals, making it safer than traditional aggressive chemical methods
- 5Both artificially placed (groomed) and naturally occurring fingerprints could be successfully visualized using this technique
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