Physicists from Harvard Medical School have created the world’s first living laser, using a cell.

Dr. Gather and Dr. Yun genetically programmed cells to produce green fluorescent proteins. They then placed such a cell in a cavity with two tiny, parallel mirrors spaced seven ten-thousandths of an inch apart, large enough to hold exactly one cell. Using a microscope, they exposed the cell to pulses of blue light.
When exposed to the pulses, the fluorescent proteins in the cells started to emit green fluorescent light. The light bounced back and forth between the mirrors, amplifying to generate a bright, unidirectional laser light.