Gold Nanoparticles Enhance Clarity of Latent Fingerprints
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Gold Nanoparticles Enhance Clarity of Latent Fingerprints In the 1941 classic film The Maltese Falcon, detective Sam Spade finds out the hard way just how dangerous gold can be—but he never suspects that one day gold might help him do his job better. In an article published in a recent issue of Chemical Communications (p. 1142; DOI: 10.1039/b618966k), M. Sametband, I. Shweky, U. Banin, D. Mandler, and J. Almog of The Hebrew University in Jerusalem, Israel, demonstrate a method of using nanoparticles of gold to significantly enhance the intensity and clarity of latent (invisible) fingerprints. The standard method for capturing latent fingerprints on wet porous surfaces has not changed in decades. Silver physical developer (Ag-PD) is applied to the surface, and the fatty components of the fingerprint residue (sebum) catalyze the deposition of metallic silver, leaving a black residue along the fingerprint ridges. However, Ag-PD is not very stable, and is not always effective at developing faint prints. Previous work has shown that gold nanoparticles applied to latent fingerprints can enhance Ag-PD deposition through an ionic interaction, in a process known as multi-metal deposition (MMD). Sametband and colleagues, inspired by this earlier work, hypothesized that hydrophobic interactions could lead to the adsorption of gold nanoparticles onto sebum-rich fingerprint ridges, and that these nanoparticles would then catalyze the silver reduction from Ag-PD, enhancing the fingerprint images. To test this idea, the researchers began with a petroleum ether solution of gold nanoparticles (Au-NPs), which were stabilized with alkanethiol chains (i.e., octadecanethiol, tetradecanethiol, or decanethiol) at different concentrations. The spherical nanoparticles were 2–3 nm 526
in diameter, roughly five times smaller than the nanoparticles used in the MMD method. The researchers next produced sebum-rich fingerprint samples on paper strips, and immersed them in the solution for times ranging from 10 s to 5 min, after which they applied Ag-PD. They found that the fingerprint impressions were significantly stronger and clearer than they were for samples without the Au-NP treatment, with optimal results using a 0.04% (w/v) solution and 3 min of immersion time. Samples without the Au-NP treatment took 10–15 min to develop. The method also worked for sebum-rich fingerprints on silicon surfaces, which are not porous. The Au-NPs stabilized with octadecanethiol aggregated better than the Au-NPs stabilized with tetradecanethiol which in turn aggregated better than the Au-NPs stabilized with decanethiol. In a final set of experiments, the researchers examined the effect of CdSe/ZnS nanoparticles on latent fingerprints, and found that aggregates of the nanoparticles adhered to the fingerprint ridges and were clearly visible under ultraviolet illumination, without the need for further chemical enhancement. In light of these results, nanoparticles may someday become a standard part of the forensic toolkit, and the Sam Spades of the future may thi
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