Researchers at Harvard University have created the first ever biological laser, using embryonic kidney cells engineered to produce green fluorescent protein. Lasers need two things two work: a material that amplifies light from an outside source, and a set of mirrors to align the light into a narrow beam. Until now, the amplifiers have all been made of non-biological materials such as crystals, gases, or semiconductors. But by placing a GFP-engineered cell between two tiny mirrors just microns apart, the team successfully created a bio-laser: when they pulsed blue light on the cell, it produced a visible laser beam about 10 times brighter than natural jellyfish fluorescence, from which GFP is derived. The technique could one day be used to target diseased cells by activating the focused light once the laser-producing cells have penetrated a target tissue, Nature reports. Furthermore, in contrast to amplifying materials in conventional lasers that degrade over time, biological cells can make more GFP continually, so the technique could produce “self healing lasers” which don’t need to be replaced, the researchers say.