It has long been well established that fingerprints can be used to identify people or help convict them of crimes. Things have gone a lot further now: fingerprints can be used to show that a suspect is a smoker, takes drugs, or has handled explosives, among other things. In the journal Angewandte Chemie, Pompi Hazarika and David Russell describe the noteworthy progress that has recently been made.
When a finger touches a surface, sweat and oil-containing substances like sebum leave behind a print that is invisible to the naked eye. There are several ways to make it visible, like dusting with powder or spraying with reagents or “superglue”. A new technique that improves sensitivity involves the deposition of gold nanoparticles attached to cage-like molecules filled with dyes or other luminescent makers that cause the fingerprint pattern to glow. Gold nanoparticles attached to antibodies against amino acids are better at revealing older, dried fingerprints.
If a person has taken drugs, traces are released in his or her sweat. A team working with Russell at the University of East Anglia (Norwich, UK) has recently developed a method by which magnetic particles are equipped with antibodies that bind specifically to certain drug or nicotine metabolites. In a second step, they apply a fluorescent antibody, which binds to the first antibody and indicates the presence of the corresponding drug by glowing under a fluorescence microscope. By using this method, the researchers were able to simultaneously detect several different narcotics in a single fingerprint.