A Better Way To Finger Criminals

Sherlock Holmes might have appreciated a pair of new techniques that make fingerprints easier to read. Daniel Mandler, Joseph Almog, and colleagues at Hebrew University of Jerusalem, in Israel, report two methods that use nanoparticles to enhance the visibility of latent prints (Chem. Commun. 2007, 1142).

Currently, fingerprints on damp, porous substrates such as paper are revealed by dipping the substrate into a silver colloid solution. But this "silver physical developer" sometimes deposits silver over the entire surface, obscuring any prints. Pretreating the substrate with gold nanoparticles suspended in an aqueous citrate solution helps but is complicated.

As an alternative, the Hebrew University researchers use gold nanoparticles stabilized by alkanethiols in petroleum ether as the pretreatment. The nanoparticles adsorb onto fingerprint ridges and catalyze electroless deposition of the subsequently applied silver. The method yields much clearer prints than the silver treatment alone.

The Israeli team's second method involves treating nonporous substrates with CdSe/ZnS nanoparticles in petroleum ether. The fingerprints then can be viewed via fluorescence under UV light.