During the analysis phase, a beam of light is bounced off the sensor. Any nanoparticles bound to the surface will change its refractive index, thereby altering the intensity of the reflected light and indicating the concentration of drugs in the sample. By immobilizing different drug molecules on different portions on the sensor surface, the analyzer is able to identify the drug traces in question. An electronic screen displays instructions and a simple color-coded readout of the results.

The test takes less than 90 seconds and can detect drugs at concentrations measured in parts-per-billion using a single microliter of saliva. The sensor is capable of even greater sensitivity--it has been used to detect cardiac troponin, a commonly used indicator of heart attack, at concentrations 1,000 times lower.

Philips plans ultimately to enter the healthcare market. It is working on a platform capable of testing blood as well as saliva and is seeking partners that can help expand its testing menu by providing it with additional biomarkers.

Other researchers have built experimental devices to magnetically detect a wide range of biomolecules in minuscule samples of blood or saliva at extremely low concentrations. Often this involves using microfluidic or magnetic forces to quickly shepherd the magnetically labeled molecules through scanners--though a group at the University of Utah has even built a prototype in which a sample-laden stick is swiped across a GMR sensor, like a credit-card through a reader.

The combination of high sensitivity, low sample volumes, miniaturization, speed, and ease of use has raised hopes for a handheld biosensor that could perform sophisticated tests with high accuracy.

"Everyone's trying to get there," says Kricka. "The question is who's going to win?" With Philips set to introduce its drug tester in Europe by the end of the year in partnership with the British diagnostics firm Cozart, the consumer electronics maker appears poised to take the prize.