Optimum conditions and application of one-step fluorescent cyanoacrylate fuming method for fingermark development based on PolyCyano UV

Abstract

Cyanoacrylate fluorescent staining has become a common method for developing latent fingermarks on light-coloured or white objects. The method requires two steps and skilled operation, and the handling process has the risk of damaging the ridge details or even biological samples. To take full advantage of the high-sensitivity fluorescence, recent research efforts on fluorescent cyanoacrylate have aimed to avoid rinsing after staining, add fluorescence to the cyanoacrylate, increase the fluorescence intensity and broaden the fluorescence spectral range. PolyCyano UV is a novel product that can be used to overcome the disadvantages associated with progressing to one-step fuming to directly develop fingermarks. To explore the optimal development conditions and application effects of PolyCyano UV, thermogravimetric differential thermal analysis, fluorescence spectroscopy and control variable analysis are used to determine and analyse the best conditions for using the reagent, including temperature, fluorescence excitation band, relative humidity and fuming concentration. The temperature range of the one-step fuming development method is 212.14 °C–275.16 °C, the wavelength range of the excitation light source is 235–580 nm, the relative humidity is 60%–80%, the concentration of the fume is 1–3 g/m3 and the specific value is related to the surface properties of the object and the aged time of the fingermarks. Additionally, fluorescence spectroscopy shows that the excitation wavelength range of the light source is 235–580 nm. Based on the best fuming condition, many common objects were selected to proceed to the application experiments, which allowed for a comparison with the traditional visualisation method, namely the Cyanobloom reagent + dyeing two-step development method. The comparison showed that latent fingermarks on most non-porous smooth surfaces, especially on light-coloured or white objects, were developed successfully. In addition, a comparative study with the conventional cyanoacrylate glue–fluorescent staining experiments showed that the effect of dyeing afterwards with Rhodamine 6 G is better than the one-step method. The effect of dyeing with BBD is basically the same as that of the one-step method. Key points: One-step fluorescent cyanoacrylate fuming can be a promising alternative for fingermarks developing based on PolyCyano UV in forensic science. The optimum application conditions of PolyCyano UV will provide guidance for fingermark examiners. The one-step fuming method based on PolyCyano UV has many advantages over the secondary dyeing method.