Styryl dye coated metal oxide powders for the detection of latent fingermarks on non-porous surfaces

Conventional fingermark powders rely on contrast induced by absorption/reflection (e.g. black powder) or luminescence in the visible region (e.g. Blitz Green1). In most cases, these powders provide sufficient contrast; however, in some circumstances surface characteristics can interfere with the visualisation of powdered fingermarks. Visualisation in the near infra-red (NIR) region, however, has been shown to eliminate interferences commonly encountered in the visible region. In this study, a mixture of rhodamine 6G and the NIR laser dye styryl 11 (STaR 11) was coated onto an aluminium oxide nanopowder and then mixed with silver magnetic powder to develop and visualise fingermarks in the NIR. When compared to Blitz Green1, it was determined that the STaR 11 magnetic powder was better suited for marks deposited on textured surfaces and for older marks, whereas Blitz Green1 performed better on smooth glossy surfaces. The ability of the STaR 11 mixed dye formulation to be visualised in both the visible and NIR regions also provides a significant advantage over conventional luminescent fingermark powders.