A plasmonic interferometry technique created by Brown University engineers has the potential to enable compact, ultra-sensitive biosensors. The method combines nanotechnology with plasmonics — the interaction between a metal's electrons and light.

The interferometry process eliminates the need for highly specialized external light sources that deliver coherent light — beams in which light waves are parallel, have the same wavelength, and travel in-phase (meaning the peaks and valleys of the waves are aligned). The plasmonic interferometers contain light emitters.

In the new method, fluorescent light-emitting atoms are integrated directly within the tiny hole in the center of the interferometer. An external light source is still necessary to excite the internal emitters, but it need not be a specialized coherent source.

Incoherent light shown on the interferometer causes the fluorescent atoms inside the center hole to generate surface plasmons. The plasmons propagate outward from the hole, bounce off the groove rings, and then propagate back toward the hole.

Because the surface plasmons travel out from the hole and back again, the plasmons probe the sample on top of the interferometer surface twice, making the device more sensitive.

Additionally, external light can be projected from underneath the metal surface containing the interferometers, eliminating the need for complex illumination architectures.

The Brown University team will next try to eliminate the external light source altogether.