Forget all the nanotechnology devoted to fighting cancer, and just consider that nanoparticles have invaded makeup, anti-odor socks, sunscreen, plastic beer bottles and home pregnancy tests. Now scientists have developed a way to assess the health and environmental impact of such nanoparticles: a tiny microresonator that can detect and measure individual particles smaller than a single virus.

The microresonator is a lab-on-a-chip that harnesses the “whispering gallery” concept that’s displayed by buildings such as St. Paul’s Cathedral in London. The cathedral’s domed gallery can carry whispers easily across to the other side, but normal-volume voices end up garbled after bouncing around the dome multiple times.

Similarly, microresonators can bounce laser light many times around a circular “waveguide,” such as a glass ring. A laser frequency must perfectly fit the circumference of a ring to achieve this whispering-gallery mode.