Exploiting an odd behavior of light boosts a biosensor platform’s sensitivity by nearly 70 times, allowing it to detect a single sample of the smallest known viruses. A peculiar behavior of light known as the “whispering gallery” mode was named after the famous circular gallery in St. Paul’s Cathedral in London, where a whisper near the wall can be heard around the gallery. The optical analog is light rays confined inside tiny circular disks or spheres, in this case a small glass bead, resonating at a specific frequency. Even something as small as a virus landing on the sensor is enough to change the resonant frequency of the light. Scientists at the Polytechnic Institute of New York University, Fordham University, and New York City College of Technology detected changes in frequency from viruses about the size of influenza — a relatively large virus — with their initial glass sphere. The system, however, was not sensitive enough to detect smaller viruses such as polio. A rendering of the whispering gallery mode sensor. (Image courtesy of Stephen Holler) By adding gold nanospheres to the glass bead’s surface, they created plasmonic “hot spots” and increased the device’s sensitivity nearly seventyfold. Then the hybrid sensor not only detected the presence of the MS2 virus — the current lightweight in the world of RNA viruses — but it also determined its weight by measuring the precise frequency change of the light. “Having achieved a detection limit below all known virus particle sizes means that medical diagnostic technology may soon be capable of rapidly detecting the presence of a single virion in blood or saliva – including common viruses such as influenza, HIV, Hepatitis and West Nile," said Fordham University assistant physics professor Stephen Holler, PhD, an author of the study. The researchers envision doctors performing diagnostic tests during office visits and “getting results in minutes, not the days necessary for current blood tests,” he said. “In addition, this sensor platform can serve as a sensitive device for monitoring for the presence of other biological and nonbiological targets for medical and security applications,” Holler said. The results appeared in Applied Physics Letters. For more information, visit: www.fordham.edu, www.citytech.cuny.edu or www.poly.edu