Microlasers inside live cells

Here we show, for the first time to our knowledge, stand-alone cell lasers with both gain medium and cavity inside cells. Cells have natural tendency to engulf micro beads made of polystyrene or glass, and we use these microspheres to generate whispering-galley-mode (WGM) lasing inside cytoplasm. The gain was provided by fluorescent dye molecules embedded in the microspheres or in the cytosol. Upon optical pumping, the output emission from the cells show characteristic WGM resonance. By analyzing the wavelengths of the oscillation modes we can determine the bead size with a precision of 50 pm. Using the mode diameter as a unique identifier, one may distinguish more than thousands of cells. Furthermore, we demonstrate real-time sensing of the intracellular refractive index changes.