Showcasing water-based delivery of an amino acid targeting fingermark developer in a hydrogel.

Most recommended methods for visualising fingermarks on paper rely on chemical developers that target and react with amino acids. Traditionally, these developers are sprayed onto paper substrates in solutions of per- and polyfluoroalkyl substances (PFAS), but now those same PFAS chemicals are undergoing phaseout or phasedown, which threatens to undermine forensic capabilities. This situation provides an opportunity to pivot towards greener approaches to fingermark visualisation. The ideal methodology would be a water-based treatment, as these provide superior safety for practitioners, combined with environmental sustainability. A major hurdle to implementing a water-based fingermark developer targeting amino acids is that water, as a universal solvent, can dissolve the eccrine components in fingermarks, as well as any optical or luminescent dyes that are created, causing the ridge detail to run or dissolve. This work circumvents this problem by delivering the amino acid developer alloxan in a hydrogel, which enables sharp fingermark ridge details to be observed despite it being a water-based treatment. Alloxan dissolved in a viscous hydrogel is shown here to react with the amino acids in fingerprint residues to form the coloured dye murexide, supported by optimisation and characterisation studies.

Preparation of a low-cost fingerprint powder that harnesses white light to emit long-lived phosphorescence.

An inexpensive, commercially available doped strontium aluminate phosphor with long-lived afterglow has been prepared and assessed in the role of a luminescent fingerprint dusting powder. Blue, green, and aqua phosphorescence persisting for ca. 30 s was obtainable from treated fingermarks after charging the powders with the white light (400-700 nm) setting of a forensic light source. Imaging the phosphorescent afterglow enabled the elimination of background emissions encountered during latent fingermark examination. This was demonstrated by visualising fingermarks on substrates that possess inbuilt fluorescent security features and highly patterned substrate backgrounds, without any need for bespoke scientific equipment.

Incorporating hydrogels into fingermark development: indicative viscosities for preserving ridge detail on paper surfaces.

Water-based fingermark development treatments for paper have long been held back by loss of ridge detail due to diffusion. Viscous hydrogels (≥2224 cP) show promise as a green method of delivering chemical developers that inhibits diffusion, thereby preserving fingermark ridge detail. This is demonstrated here with starch and xanthan gum hydrogels applied to iodine-fumed fingermarks.