A class of devices based on LEDs promises to enable the development of cost-effective smart sensors. Researchers at the University of Wisconsin have demonstrated that the chemical sensors, fabricated from standard semiconductor materials, can detect amine gases and sulfur dioxide over a range of concentrations. The devices offer a number of advantages. "They use very little power," said Arthur Ellis, a professor of chemistry and a member of the research team. "They're lightweight. One could imagine using arrays of these." The sensors consist of interdigitated fingers of edge-emitting LEDs. The team has used 670- and 890-nm diodes. Half of the fingers are forward-biased and give off light, and the others are reverse-biased and act as detectors. The two are separated by microns. When exposed to a chemical, the detected light changes according to the concentration of the chemical. The finger design offers a large surface area for increased responsivity. The sensors display a rapid response to a sample, as well as reversibility when the chemical is removed. Expanded sensing Ellis said that the sensors, which the team described in the Jan. 25 issue of Nature, could be modified to detect a wider array of chemicals under a greater range of conditions by coating the sides of the LED fingers with thin films. When exposed to a specific chemical, the thin film would alter the light, creating a chemical-specific sensor. Other coatings might enable the device to function as a sensor for liquid samples, he added.