The St. Andrews team accomplished this by coaxing each cell to engulf a tiny plastic bubble (the green dot in the image above) that acts as a resonant cavity. Each bubble is precisely sized and imbued with fluorescent dye. When a laser hits the cell, it excites the dye which bounces around and amplifies inside the bubble, then fluoresces at a different wavelength. Interestingly, the color of the light that the cell emits depends on the size of the bubble. So far, the researchers have gotten cells to produce light at three different wavelengths. And while the team has only been able to get the method to work in petri dishes, they hope to further develop it into a means of tracking specific cells -- say, tumor cells -- for days, even weeks.

[Image Credit: top - Arbi Babakhanians, inline - M. SCHUBERT ET AL., NANOLETT (2015); ACS]