Effects of ultraviolet exposure on latent fingermark visualization on expanded polystyrene surfaces

It is known that the physical and chemical properties of expanded polystyrene (EPS) surfaces are altered upon exposure to ultraviolet (UV) light; however, the implications for latent fingermark visualization have not been fully explored. In this study, EPS surfaces were exposed to UV light (253.7 nm) either before or after fingermark deposition and subsequently treated with five visualization techniques: Dazzle yellow, cyanoacrylate fuming (CA) followed by fluorescent dye staining, Lumicyano, small particle reagent (SPR), and Nile red. When illuminated with a blue or green forensic light source, photoluminescence was observed exclusively on UV-exposed surfaces, allowing clear differentiation between UV-exposed and unexposed EPS. Experimental results indicated that Nile red produced the highest-quality fingermarks on unexposed EPS surfaces, while Dazzle yellow and Nile red were most effective for UV-exposed surfaces. In contrast, CA followed by rhodamine 6G staining (CA/R6G) and Lumicyano methods exhibited markedly reduced performance on UV-exposed EPS due to photochemically induced surface alterations. These findings highlight the importance of assessing UV exposure prior to fingermark development and suggest appropriate visualization methods based on surface condition.