Reading a Letter from the Envelope it Was In
Paul Kelly and colleagues at Loughborough University found that a disulfur dinitride (S2N2) polymer turned exposed fingerprints brown, as the polymer reaction was initiated from the near-undetectable remaining residues.
Traces of inkjet printer ink can also initiate the polymer. The detection limit is so low that details of a printed letter previously in an envelope could be read off the inside of the envelope after being exposed to S2N2.
“A one-covers-all versatile system like this has obvious potential,” says Kelly.
“This work has demonstrated that it is possible to obtain fingerprints from surfaces that hitherto have been considered extremely difficult, if not impossible, to obtain,” says Colin Lewis, scientific advisor at the UK Ministry of Defence. “The method proposed has shown that this system could well provide capabilities which could significantly enhance the tools available to forensic scientists in the future.”
Roger • November 11, 2008 8:59 AM
A rather dangerous reagent; it explodes if allowed to warm up to 30°C (86°F). It has to be generated in situ, and Kelly observes that the design of the generator “precludes portability.”
This polymer, by the way, is both an electrical conductor (a bit unusual), and also superconductor (but only at very low temperatures, colder than the boiling point of helium.)
One wonders if these properties could be used to detect the polymerisation at concentrations too low to leave a visible mark?
Wow. That is impressive. And not stated here, but described in the original article, the process is so sensitive they can even get an image through two sheets of paper — so folding the letter so the ink faces inwards will not help much (although it will make reading harder, by superimposing more letters.)
One wonders, though, how much the image would be blurred if the letter could move around inside the envelope, instead of being held in place by a paperweight for the whole exposure period?