An ultrasensitive, whispering-gallery-inspired biosensor has set a record, identifying the smallest known single virus particle. The biosensor derives its name from the peculiar behavior of light that is named after the famous circular gallery in St. Paul’s Cathedral in London, where a whisper near its wall can be clearly heard at any point in the gallery. At the heart of the sensor is a small glass bead, inside which are light waves that resonate at a specific frequency. Something as small as a virus landing on the sensor, however, is enough to change the resonant properties of the light. A rendering of the whispering-gallery-mode sensor created by scientists at the Polytechnic Institute of New York University, Fordham University and New York City College of Technology. The device is sensitive enough to detect the smallest known single virus particle. Courtesy of Stephen Holler. Scientists at 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 bead. The system, however, was not sensitive enough to detect smaller viruses such as polio. By adding gold nanospheres to the glass bead’s surface, the team created plasmonic “hot spots” and enhanced the device’s sensitivity nearly seventyfold. The hybrid sensor not only detected the presence of the MS2 particle – a lightweight RNA virus – but also determined the virus’s weight by precisely measuring the frequency change of light. Inspiration for the technology came to NYU-Poly applied physics professor Stephen Arnold while watching a performance by violinist Itzhak Perlman. “I was watching Perlman play, and, suddenly, I wondered what would happen if a particle of dust landed on one of the strings,” Arnold said in a university release. “The frequency would change slightly, but the shift would be imperceptible. Then I wondered: What if something sticky was on the string that would only respond to certain kinds of dust?” With some tweaking, the sensor should be able to detect single proteins, such as cancer markers that appear in the blood long before outward signs of the disease can be detected. The findings were reported in Applied Physics Letters (doi: http://dx.doi.org/10.1063/1.4739473).