Evaluation of diazonium gold(III) salts in forensic chemistry: Latent fingerprint development on metal surfaces

Abstract

Evaluation of diazonium salts in forensic chemistry will vastly benefit in the design of novel developers for latent fingerprints on metal surfaces used as crime tools. We used the easily reducible aryldiazonium salt stabilized with tetrachloroaurate anion of the formula [NO2-4-C6H4N≡N]AuCl4. Localized elemental analysis, after 2 h of contact with the aryldiazonium salt, using X-ray fluorescence (XRF) and energy dispersive spectroscopy (EDS) showed the deposition of gold on the fingerprints collected on copper, lead and aluminum. Poor development obtained from the non-gold aryldiazonium salt [NO2-4-C6H4N≡N]BF4, in addition the temporal evolution of the deposition over 24 h showed images of poor contrast and scattered minor deposits. It can be noticed from the images collected using scanning electron microscopy (SEM) and stereomicroscope that the grafted film was not filling the grooves but selectively adhered to the eccrine prints on copper and lead however showed indiscriminate deposition on aluminum surface at high concentrations. Obliteration of developed fingerprints was not observed on all surfaces. The degraded contrast on aluminum after the visible overflow of the trenches is a limitation of diazonium on highly reactive metal surfaces according to the electrochemical series. It can be concluded that copper surface is the most successful among the three metals. The gold film aided to visualize the three levels of primary, secondary and tertiary fingermarks at high level of details. Reduced gold on fingerprints can be beneficial in archiving and future analysis.