Angew. Chem. Int. Ed. http://doi.org/fz9b7k (2012)

Angew. Chem. Int. Ed. http://doi.org/fz9c72 (2012)

When a finger, palm or foot comes into contact with a smooth surface, the ridged surface on the skin leaves a mark known in forensic science as the friction ridge pattern or, if it is not visible to the naked eye, a latent fingermark. These fingermarks contain a complex mixture of secretions from pores on the ridges of the skin and can be detected using various optical, physical and chemical techniques. Adding to this toolbox of methods, two independent research teams have now developed two techniques for visualizing latent fingermarks.

Philip Maynard and colleagues at the University of Technology, Sydney and the University of Canberra used DNA aptamers that can recognize lysozymes (a component found in human sweat) to bind to fingermarks and produce marks with well-defined features. Fingermarks imprinted on a polyvinylidene difluoride substrate were aged for 24 h and then treated with a solution of fluorescently labelled DNA aptamers for 1 to 4 h. The marks were then imaged with a 505 nm light source, which revealed fingermarks with strongly fluorescent ridges and dark valleys.

Alternatively, Joseph Almog and colleagues at the Hebrew University of Jerusalem used gold nanoparticles modified with a bifunctional molecule to produce 'negative' fingermarks on cellulose paper. The gold nanoparticles bind to the cellulose paper but not to the fingerprint. On development in a silver solution, dark silver precipitates formed on the gold-coated areas giving rise to uncoloured fingermarks against a dark background. The process requires only 5 min of treatment with the nanoparticles, followed by 40 to 60 s of development.