Coated quartz for detecting toxics.

Coated quartz for detecting toxics

Quartz crystals coated with proteins such as antibodies, enzymes and other biologically active materials may be useful for detecting traces of pesticides and drugs in air. This technique is potentially simpler and cheaper than currently available methods for recognizing and measuring small concentrations of toxic substances.

In the Sept. 3 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, chemist George G. Guilbault of the University of New Orleans and his colleagues report success in using quartz crystals coated with antibodies against the pesticide parathion to measure parathion concentrations down to 36 parts per billion. "The results obtained in this study," the researchers say, "demonstrate that a piezoelectric crystal coated with a specific antibody could be used as an analytical tool in gas-phase analysis."

Each quartz crystal has two surface electrodes, which are coated with a specific agent known to bond with the substance to be measured. For example, parathion antibodies would pick up the antigen parathion. Normally, an electric current drives the crystal to oscillate at a set frequency. When an antigen-carrying gas flows over the crystal, the coated surfaces collect the antigen and as a result grow heavier. This weight increase changes the crystal's frequency, providing a measure of the antigen's concentration in air.

The researchers found that their antibody-coated crystals last for several weeks. Passing pure air over the used sensors reverses the antibody-antigen reaction and restores the crystals to their original state. The same frequency signal is observed before and after repeated exposure to antigen.

Although protein-coated quartz crystals have been used before to detect specific substances, those reactions have all taken place in liquids. The new results, says Guilbault, are the first to show that the analysis can be done directly in the gas phase. Guilbault has a small company that holds a patent on this technique.

Guilbault is now developing antibody-based sensors for detecting cocaine, morphine and heroin in air. These sensors, he says, would be able to detect levels that a dog's nose can sniff out. "But you don't have the upkeep and the mess that you have with dogs," says Guilbault.

However, the researchers say, while a great deal is known about antigen-antibody interactions in solution, much less is known about their behavior in the vapor phase. These aspects will have to be studied further before a practical sensor is ready.