Understanding The Polymerization of Ethyl Cyanoacrylate in the Superglue Fuming of Latent Prints To Optimize Print Retrieval

The cyanoacrylate fuming method (CFM) is a widespread process used in forensics to make latent prints visible for detection, acquisition, and analysis. CFM is governed by the reaction of ethyl cyanoacrylate (ECA) with biological components in fingerprints, which serve as initiators for this anionic polymerization. CFM is not a well-controlled polymerization and there are different outcomes that may result from lower temperature, one of which fits the generalization of creating more ion-pair initiators. Another effect could be minimizing termination through suppressing side reactions. Alternatively, when paired with humidity, lower temperatures may cause surface condensation, decreasing the quality of the print. This work encompasses experiments in which fingerprints on glass undergo the CFM while simultaneously controlling surface temperatures and relative humidity to prevent quality degradation. The resulting fingerprints were assessed by direct mass measurements and the molecular weight analysis via gel permeation chromatography (GPC). This provides insight into the coupling effects of temperature and humidity on the cyanoacrylate fuming method at the molecular level in order to design a more effective quantitative and qualitative protocol for forensic scientists for the retrieval of latent prints.

Post-treatment of fingerprints to increase contrast between the fumed print and the surface of deposition has led to the introduction of different ECA formulations. One of interest is Lumicyano which combines ECA with a fluorescent powder before fuming, decreasing the need for additional steps post-fuming which saves overall processing time of evidence. Lumicyano and Sirchie ECA (“unmodified ECA”) were used to perform CFM with different methodologies, altering surface temperature and fuming time in order to assess any variation in polymeric properties based on formulation.

A plethora of surfaces can be encountered at crime scenes. The surface of fingerprint deposition can alter the procession of polymerization through the interactions with components of the deposited print or through the behavior of the surface itself could alter CFM results. Our research investigated the changes in PECA grown on fingerprints deposited on glass, poly(ethylene terephthalate) (PET), and brass to explain how fuming on glass, plastic, and metal affect the resultant polymer and consequently, the ideal parameters for fingerprint visualization.