Go: detect!

''Their idea uses a thin layer of metal drilled with nanoscale holes, laid onto the surface being tested. When the perforated plate is zapped with laser light, the surface plasmons that form emit light with a frequency related to the materials touching the plate. A sensitive light detector is needed to measure the frequency of light given off.
...
The team says devices using this approach can be small and portable, will work on very low power, and could detect everything from explosives to bacteria.''

Source here.