Portable Cocaine Sensor Developed at UC Santa Barbara

A real-time sensor for detecting cocaine—made with inexpensive, off-the-shelf electronics—has been developed by a team of researchers at the University of California, Santa Barbara. Two local high school students and a Nobel laureate participated in the discovery. Their article was published in the Journal of the American Chemical Society.

To create the sensor, the researchers took a DNA molecule that converts from a floppy and unfolded shape into a structured, folded shape in the presence of cocaine. They then observe the change in the DNA by monitoring how electrons travel through it. There are DNA molecules available that bind to many different targets, so it follows that similar sensors can be easily made for other targets.

Currently the cocaine sensor that is widely used by police is the Scott test. When a chemical is added to the white powder it changes color, but some cocaine manufacturers add a chemical to block the color change. "Our sensor can detect cocaine no matter what they have cut it with: powdered sugar, flour, or the coffee that is sometimes used to mask the smell from dogs," said Kevin Plaxco, associate professor of chemistry and biochemistry.

At this point the new sensor detects cocaine in the blood or saliva to a degree of a few micromolars. This is equivalent to the concentration of cocaine that would result from dropping a kilogram of cocaine into an Olympic-sized swimming pool. That concentration would be the equivalent of detecting 3 parts per million in blood. Still, this is not yet sensitive enough for use in the emergency room, since a person with 0.3 parts per million of cocaine in their blood would be considered "stoned on cocaine," so more work needs to be done to increase the sensitivity of the new test. The sensor can be housed in supporting electronics that are the size of a small hand-held device.

Co-author and Nobel laureate Alan Heeger said: "We have developed a method of detecting small molecules and proteins in a way that is not specific to cocaine—a whole class of biosensors can be based on this concept. It can be applied to the prevention of bioterrorism. It is beautiful work; the sensor is fully portable."

The potential medical implications of the sensor for detection of prescription drugs may be profound. A drug like cyclosporin, an immunosuppressant that has revolutionized the field of organ transplants, must be carefully monitored in a patient's blood to regulate the dosage. The test to check the ratio of a therapeutic dose versus a lethal dose is a process that takes six hours. With the new sensor, the blood level of the drug could be immediately detected and deaths could be prevented. Another drug requiring this type of careful regulation is a family of antibiotics known as aminoglycosides.

Some patients metabolize a certain drug quickly and others slowly. Because of this vast variance, there are drugs that have not been introduced to the market because of the need for an immediate check of the blood level of the drug in order to prevent death. Plaxco explained that new drugs may be made available when this sensor is applied to this medical use.