That metal ball that makes your hair stand on end at science museums may have a powerful new use. Scientists have found a way to combine these Van de Graaff generators with a common laboratory instrument to detect drugs, explosives, and other illicit materials on the human body.
The laboratory instrument in question is a mass spectrometer. These machines ionize samples of liquids, solids, or gases, imparting an electrical charge that can be used to identify them. That’s tricky for detecting substances on humans, says Kwan-Ming Ng, a chemist at the University of Hong Kong. “The major obstacle is safely depositing a sufficient amount of energy on the human body to induce ionization of chemicals on their skin.”
Ng had the idea of coupling a Van de Graaff generator, a powerful but safe way to electrostatically charge the skin’s surface, with a mass spectrometer. Touching the Van de Graaff generator for only 2 seconds charges a person’s body to 400,000 volts, which ionizes compounds on the surface of the body. Then, the person would point the part of their body to be tested, such as a finger, toward the inlet of a mass spectrometer, and ions from their body would enter the machine. Also, chemicals in the breath would become ionized as the person exhaled and the chemicals passed through their electrostatically charged lips.
Ng and his co-workers tested the new method, which they call Megavolt Electrostatic Ionization Mass Spectrometry, on a volunteer, who handled different substances such as explosives, flammable solvents, cocaine, and acetaminophen. Then, the person placed one hand on a Van de Graaff generator and moved his other hand in front of the inlet to a mass spectrometer. The mass spectrometer correctly identified each of the tested substances, the team will report in an upcoming issue of the Journal of the American Society for Mass Spectrometry.
The method could also detect compounds in the breath of four healthy volunteers who exhaled through a straw into the mass spectrometer inlet while touching the Van de Graaff generator, Ng says. After a person chewed mint-flavored gum or drank red wine, the mass spectrometer detected chemicals from the gum and wine in their breath. Therefore, the method might help diagnose diseases characterized by certain chemicals in the breath, such as diabetes, or detect drugs or alcohol on the breath of suspects.
The technique is fast, providing a readout within seconds. And according to Ng, the Van de Graaff generator does not produce an electric shock, although people may experience an itchy “ion wind,” and their hair will stand on end during the short period of time that the generator is turned on. He stresses that despite the high voltage generated, the metal ball is safe, as it has been demonstrated in countless science displays at schools and museums.
The new method may be useful for security checkpoints at airports or other public places, where officers could quickly and easily determine whether a person has recently handled explosives or illicit drugs. However, existing mass spectrometers will need to be modified to withstand the high electrostatic charges and other rigors of repetitive on-site testing, Ng says.
For security screening, Ng envisions that the technology will take the form of a chamber connected to a Van de Graaff generator. People would enter the chamber, and ions from all over their bodies would be channeled into a mass spectrometer. This setup would be more sensitive and less invasive than current ways to detect trace explosives or drugs on a person’s body, such as specially trained dogs.
John Yates III, a chemist at the Scripps Research Institute in San Diego, California, is surprised by Ng’s findings. “I never would have thought to try this experiment, nor would I have thought that ions could be produced off someone’s skin or breath using a Van de Graff generator,” he says. Further work must be done to establish the sensitivity and safety of the method, Yates says. For example, touching a Van de Graaff generator is generally not recommended for people with a pacemaker or other electronic medical device.
“This study is cute, clever, and interesting,” says Joseph Loo, a chemist at the University of California, Los Angeles. “It highlights how mass spectrometry could be used in everyday life in the future.”
However, Loo notes that obtaining approval from federal agencies to use Van de Graff generators for human subjects may be difficult, given the hurdles the U.S. Transportation Security Administration had to overcome to implement new scanners in airports after 9/11. “And you can imagine the reaction that some people might have by being told to touch this surface and, ‘No need to worry; it’s only 400,000 volts.’ ”