A Fast and Simple Cocaine Detector

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Jon Faiz Kayyem, cofounder of Clinical Micro Sensors, a biotech company that was bought by Motorola, says Plaxco's design has strong potential for broad use because it's cheap to make and easy to use. "For years, scientists have been reporting fantastic results, such as detecting a single particle of anthrax in a lung full of air. But you don't find those out there in real use. Most devices don't give attention to the person running the test, paying for the test, or making the test," he says.

The versatility of the design is also important. "There are lots of one-off individual tests for proteins and small molecules that rely on molecular weight or binding tests," says Kayyem. "But there is no good way to do small molecule and protein testing that allows you to take a single sensor and test for lots of different things. It would be a leap forward in efficiency to have a single machine to test for almost any small molecule using the folding DNA approach," he says.

One of the primary uses that Plaxco envisions for the device is to detect the levels of different drugs in a patient's blood. This kind of information could help doctors if they suspect a drug overdose. It could also be used to monitor the levels of prescription drugs that must be kept at a specific concentration in the body.

Scientists still have a few problems to work out before the tests can be used in the clinic. "This work is a clear step forward...However, the reported sensing technique must be further refined to enable clinically useful detection limits," says Aimee Rose, a specialist in organic-based chemical sensors at Nomadics, a security technology company with offices in Cambridge, MA. The device can currently detect cocaine in blood or saliva to a few micromolars. For routine drug testing, though, it would need to be able to detect picomolar concentrations, or a million times more dilute.

Rose speculates it will be challenging to make the device three orders of magnitude more sensitive. However, Kayyem says "there are lots of tricks in the yard for improving sensitivity, so I don't see that being a permanent barrier."

The sensitivity issue will play a role in other applications as well. The team has created DNA sensors to detect viral DNA present in the blood stream. The device has a lower detection limit of approximately 60 million DNA molecules per milliliter, which is about four orders of magnitude poorer than that needed for clinically relevant HIV detection, says Plaxco.

The team is now working on a sensor to detect a protein that appears to be diagnostic for several forms of cancer. Plaxco says proteins may be a better target for diagnostic purposes, because they tend to be detectable at clinically relevant concentrations in the blood.