Updating procedures in forensic chemistry: One step cyanoacrylate method to develop latent fingermarks and subsequent DNA profiling

Fingerprints play a key role in crime scene investigations because their friction ridges pattern can be used for identification purposes. In most cases, fingermarks are invisible and influenced by substrates or environmental factors. Latent fingermarks, on non-porous substrates, developed by traditional cyanoacrylate fuming process, often lack contrast with the substrates; therefore further enhancements are required, such as dye staining or powder dusting. This second step, that is part of the conventional detection, aims at improving contrast and at increasing the legibility of details. To avoid the second step, several commercially available formulations of cyanoacrylate have been recently manufactured and marketed as “one-step” fuming reagents for latent fingerprints visualization. In particular, Lumicyano is found to be very promising, combining the cyanoacrylate fuming and the dyeing procedures into a one-step process offering the potential to save time and effort in the detection of latent fingermarks. In this work, a detailed comparative examination between conventional, two steps process (cyanoacrylate fuming followed by staining with Basic Yellow 40) and Lumicyano is proposed for fingerprints detection, in cooperation with the Scientific Investigation Department (Carabinieri-RIS) of Rome. The study has been conducted on fresh and aged fingermarks (up to 100 days) and applied to non-porous surfaces without changing the fuming chamber settings of forensic laboratories. Fingermarks has been detected with UV Reflection (λ 254 ) using SceneScope RUVIS instrumentation; furthermore, marks have been observed under white light and in fluorescence (λ 415 e λ 515 ) with crimescope system in order to ensure a good compatibility with the forensic light sources available within most police forces. The Lumicyano fluorescence decay was also evaluated up to 20 days. The possibility of further DNA detection after marks visualization, has also been investigated to propose a novel approach able to detect fingermarks and DNA from the same forensic trace. Furthermore, NMR analysis was performed to get some information about the interaction between the ethyl-2-polycyanoacrylate and 3-chloro-6-ethoxy-1,2,4,5-tetrazine (Lumicyano post fumigation) as well as to understand whether the fluorophore binds covalently the polymer formed on the ridges. The results indicate that good ridges clarity and excellent contrast are observed with one-step process, concluding that Lumicyano detects fingermarks with equal or better sensitivity and ridge details than currently used cyanoacrylate, allowing marks’ acquisition ever after 100 days. This study has shown that further enhancement with Basic Yellow 40 (BY40) after Lumicyano can still be carried out if required, allowing the visualization of marks using a different combination of incident/emission longwave, for best performing results. Moreover, Lumicyano was found to be compatible with a subsequent DNA. The results of NMR analysis show that there is no chemical covalent bond between fluorophore and polymer.