The system was devised by Seok Hyun Yun and Matjaž Humar, two optical physicists from Harvard University, and uses oil or fat droplets to reflect and amplify light, basically generating a laser whenever needed. For these microlasers, the spectrum is more narrow, in the 500-800 nanometre range, making it easier to label cells with light, says Jeffrey Karp, a bioengineer at Brigham and Women’s Hospital in Boston, Massachusetts.

First, they injected cells with tiny oil droplets to form a cavity that could be filled with fluorescent dye. Changes in the shape of the droplet induced by miniscule pressure alterations within the cell altered the spectra of light emitted, and those alterations could be readily measured. While at first it might seem as practical as attaching lasers to sharks’ heads, the technology actually has great potential in biomedical applications for tracking individual cell movements within a living body.

The key to building a laser inside a cell is creating an optical microresonator-a miniature version of this setup that confines light so that it circulates inside a small sphere, where it’s trapped by refraction at the sphere’s surface.

In another, tiny polystyrene beads were ingested by a type of white blood cells called a macrophage and used to perform functions similar to the oil droplets.

Yun and Humar used three different methods to create their intracellular “micro-lasers”.

“The fluorescent dyes now used for research and for medical diagnosis are limited because they emit a very broad spectrum of light”, explains Seok Hyun Yun, PhD, of the Wellman Center for Photomedicine at MGH, corresponding author of the report. “They could eventually provide remote sensing inside the human body without the need for sample collection”. Cells are smart machines, and we are interested in exploiting their awesome capabilities by developing smart-cell lasers that might be able to find diseases and fire light at them on their own. In both instances, pumping our bodies by using a heart beat of light provided a residing laser beam, like the light got rubbed on inside and of course the chamber shone. “Imagine rather than a biopsy for a lump that doctors suspect to be cancer, cell lasers helping determine what it’s made of”.

The new method could also make is much easier to distinguish between different cells.