When treating epilepsy, doctors adjust the drug dose almost blindly. Too little, and seizures continue; too much, and side effects appear. Usually, a patient's blood is sent to a lab, and the result comes back a day or two later. Now, the same test can be done on a tiny silicon chip.
The sensor works like a highly sensitive nose. A dried drop of blood is illuminated with an infrared beam, and drug molecules absorb light at their specific wavelength. The more drug present, the stronger the absorption. The scientists tested the chip on phenytoin, a common epilepsy medication. The sensor detected a concentration of 2.2 milligrams per liter, even though the therapeutic range starts at 10 milligrams per liter. This means it can catch a dose that's too low.
The silicon base makes the sensor cheap and compact. Such chips could be mass-produced by the millions, like ordinary electronics. In the future, a doctor could check drug levels right in the office, without waiting for a courier from the lab.
The infrared light used by the sensor is the same kind of heat emitted by the human body, just tuned to a precise wavelength.