The technology has its roots in a peculiar physical phenomenon known as the "whispering gallery," described by physicist Lord Rayleigh (John William Strutt) in 1878 and named after an acoustic effect inside the dome of St Paul's Cathedral in London.
It happens because sound waves travel along the walls of the dome to the other side, and this effect can be replicated by light in a tiny glass sphere just a hair's breadth wide called a Whispering Gallery Resonator (WGR).
Photons bouncing along the interior of the tiny sphere can end up travelling for long distances, sometimes as far as 100 meters.
Monitoring these color changes allows scientists to use the WGRs as a sensor; previous research groups have used them to detect individual virus particles in solution, for example.
"We heated a small glass tube with a laser and had air blown down it - it's a lot like traditional glass blowing".
Blowing the air down the heated glass tube creates a spherical chamber that can support the sensitive light field.