By affixing nanoscale gold spheres onto a microscopic bead
of glass, researchers have created a super-sensor that can detect even single
samples of the smallest known viruses (see paper in Applied Physics Letters:
"Taking whispering gallery-mode single virus detection and sizing tothe limit"). The sensor uses a peculiar behavior of light known as
"whispering gallery mode," 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.
In a similar way, waves of light are sent whirling around
the inside of a small glass bead, resonating at a specific frequency. Just as a
small object on a vibrating violin string can change its frequency – ever so
slightly – so too can a virus landing on the sensor change the resonant
frequency of the light.