Researchers at Washington University in St. Louis, United States, have developed a tiny doughnut-shaped laser sensor that detects very small particles, such as viruses, salt and soot. Virus particles can make us sick, salt particles trigger cloud formation, and soot particles can lodge in our lungs and make it harder to breathe. With the new sensor, light traveling around the micro-laser is disturbed by a particle landing on the ring, thus changing the light’s frequency. The sensor is comprised of glass laced with atoms of certain rare earth elements. A particle’s size and refractive index determine the effect of the particle on the lasing mode. As particles enter the “mode volume” of the micro-laser, a discrete upward or downward jump in the beat frequency signals the binding of a particle to the ring, and the number of jumps determines the number of particles. According to Lan Yang, PhD, an assistant professor of electrical and systems engineering who led the team that fabricated the sensor, there is already interest in its commercialization in fields ranging from biology to aerosol science. Near term uses “will be the monitoring of dynamic behaviors of particles in response to environmental and chemical changes at single particle resolution,” said Yang, and the next step will be to see if the microlasers can be engineered to detect DNA and individualized biological molecules. The sensor is described in the online edition of the journal Nature Nanotechnology.