"This use of nanotechnology in the fingerprint community can bring novel and practical solutions to develop and enhance latent fingerprints that would otherwise remain undetected," says Claude Roux of the Centre for Forensic Science at the University of Technology in Sydney, Australia.
Today, the standard way of revealing hidden fingerprints on wet, porous surfaces, such as paper and cardboard, involves coating the surfaces with an aqueous suspension of gold nanoparticles and citrate ions. Under acidic conditions, the gold particles adhere to the positively charged particles from fatty residues in the fingerprint. The print is then developed using a reagent called silver physical developer (Ag-PD), which reacts chemically to create a black silver precipitate along the fingermark ridges. This process is based on an electroless deposition reaction, in which Fe2+ ions reduce the Ag+ ions to metallic silver – a reaction that is catalysed by the fatty components of fingermark material.
However, the developing solution used in this technique is unstable and results are difficult to reproduce. Now, Matias Sametband and colleagues of the Hebrew University of Jerusalem have developed a more stable solution by dissolving the gold nanoparticles in petroleum ether, capped with different hydrocarbon chains, known as thiols. The gold nanoparticles adhere to the fingermark residue and then catalyse the precipitation of metallic silver from the Ag-PD solution.
The prints produced by the new solution are very high quality and can be developed after just three minutes (see figure). Moreover, the researchers found a clear relationship between the chain length of the stabilizing thiols and fingerprint quality: the longer the chains, the clearer the fingermarks.
The team has also extended its technique for use on non-porous surfaces, using a petroleum ether suspension of cadmium selenide and zinc sulphide. Here, the chemical reaction makes the prints fluoresce under ultraviolet light, so no extra development stages are required.
Antonio Cantu, a forensic science expert for the US Secret Service in Washington, says the new technique is "revolutionary" and could greatly improve the recovery of latent prints on evidence.
The researchers reported their work in Chemical Communications.