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Cocaine Biosensor
Aaron Rowe writes "The MIT Technology review reports that a lab at UC Santa Barbara has created a biosensor by attaching a special type of DNA called an aptamer to a gold electrode. When cocaine is present, the aptamer tightly hugs a cocaine molecule and leans over so that a metal tag can touch the gold surface. This causes a spike in a plot of current versus voltage when the electrode is attached to a machine called a cyclic voltmeter."
Gold being soft means less force is required to make a good low-resistance electrical contact. So gold is the king of conductors for contact applications. Add to that the fact that it doesn't corrode or oxidize under normal conditions, it beats the two better conductors (at room temperature), silver and copper.
Researchers can obtain a license from the DEA to acquire (from a company possessing a DEA license to manufacture/distribute, which every major chemical company like Mallinkrodt or Sigma Aldrich has) and possess controlled substances. It's not easy to get, they obsessively track what you purchase and you have to file paperwork accouting for every last bit of it, but many such licenses exist. For more information on obtaining such licenses, see: http://www.deadiversion.usdoj.gov/drugreg/index.ht ml
How they get the coke for testing?
It's simple. Somebody whips out a twenty dollar bill out of their pocket, because ten out of eleven bills have cocaine on them.
Take the cheese to sickbay, the doctor should see it as soon as possible - B'Elanna Torres, "Learning Curve"