Validation of PolyCyano UV : A One-Step Luminescent Cyanoacrylate Fuming Process

PolyCyano UV (Foster + Freeman Ltd) is a new one-step process for developing luminescent fingermarks using cyanoacrylate (CA) fuming without the need for further chemical treatment. Once an exhibit is fumed, it can be imaged under a long-wave UV light source. This method is particularly recommended for substrates that are easily destroyed or degraded during solvent-based staining processes. By avoiding the use of hazardous chemicals and solvents, this method also has significant health and safety advantages. In this study, conditions including the amount of PolyCyano UV powder, the humidity level of the fuming chamber, and the time and temperature of the fuming process were optimised. A variety of different surfaces were tested and aged fingermark samples were also examined. The PolyCyano UV developed fingermarks were compared to conventional CA-developed fingermarks and subsequently stained with rhodamine 6G. PolyCyano UV was able to develop high quality fingermarks on the surfaces tested, however, when examined under UV light, the luminescence of PolyCyano UV developed fingermarks was found to be weaker than conventional CA-developed fingermarks that were stained with rhodamine 6G. When used in sequence with rhodamine 6G, PolyCyano UV was found to give significantly improved contrast compared to conventional CA-developed fingermarks stained with rhodamine 6G. Cyanoacrylate Enhancement Techniques Although cyanoacrylate (CA) fuming is a widely used and reliable fingermark detection and enhancement technique the developed marks often lack contrast and can be difficult to visualise, particularly on light coloured surfaces. Techniques to increase contrast include optical methods such as episcopic coaxial illumination [1], fingerprint powder and most commonly applying a coloured or luminescent stain. The advantage of using a stain is that the dyes will be trapped in the cyanoacrylate polymer, significantly enhancing contrast. Different stains can also be used depending on the surface [2]. Commonly used stains include rhodamine 6G, Ardrox® and basic yellow 40, each with different excitation and emission characteristics. There has been a wide range of studies examining the effectiveness of these dyes as well as proposing alternative methods and dye mixtures [3-5]. Recently, several new products have become commercially available (PolyCyano UV, LumicyanoTM, CN-YellowTM) that can develop luminescent fingermarks in a one-stage fuming process, without the need for further chemical enhancement. These techniques have several advantages: the one-step fuming and staining process is more efficient, minimises the use of hazardous chemicals and can be used on surfaces that cannot be treated with a conventional stain solution (e.g., semi-porous surfaces). The concept of a luminescent cyanoacrylate polymer has been investigated since the 1980s; however, there has been limited success. The first reported successful one-step cyanoacrylate fuming process was by Weaver and Clary, who combined methyl cyanoacrylate with dye from the styryl family. This work was published and patented, the resulting product is marketed as CN-YellowTM [6]. A similar method was proposed by Takatsu, who used p-dimethylaminobenzaldehyde (DMAB) crystals as a vapour staining method of enhancing CA-developed fingermarks. DMAB treated marks exhibited strong luminescence under UV radiation; however, they proposed it as a two-step method [7]. The material safety data sheet (MSDS) for PolyCyano UV confirms that DMAB is used in this product [8]. PolyCyano UV was previously evaluated by Hahn and Ramotowski and developed marks were compared to those treated with different luminescent CA stains. This study found that the PolyCyano UV produced luminescent fingermarks of comparable quality to the stained fingermarks on a range of different surfaces. Similar to conventional CA, the effectiveness of PolyCyano UV was found to be highly dependent on the surface itself [9]. A limitation of the study was that it used a modified fuming cabinet to deliver the PolyCyano UV powder into the glue dish and did not use commercially available equipment.