Intracellular microlasers

Optical microresonators(1), which confine light within a small cavity, are widely exploited for various applications ranging from the realization of lasers(2) and nonlinear devices(3-5) to biochemical and optomechanical sensing(6-11). Here we use microresonators and suitable optical gain materials inside biological cells to demonstrate various optical functions in vitro including lasing. We explore two distinct types of microresonator-soft and hard-that support whispering-gallery modes. Soft droplets formed by injecting oil or using natural lipid droplets support intracellular laser action. The laser spectra from oil-droplet microlasers can chart cytoplasmic internal stress (similar to 500 pN mu m(-2)) and its dynamic fluctuations at a sensitivity of 20 pN mu m(-2) (20 Pa). In a second form, whispering-gallery modes within phagocytized polystyrene beads of different sizes enable individual tagging of thousands of cells easily and, in principle, a much larger number by multiplexing with different dyes.