Various devices that permit the emission of light are known as luminescent probes and are cornerstones of the cellular biology and medical fields. Light is emitted at various frequencies due to atoms or molecules making a transition from a higher to a lower energy state. These various emissions comprise an emission spectrum. The molecular probes used in these fields typically have a very broad emission spectrum, limiting the number of probes that can be used to accurately obtain information.
Researchers from Harvard University have generated stand-alone cell lasers based on light-confining structures on a micrometer-scale known as microresonators. Their recent paper describes intracellular whispering-gallery mode (WGM) microresonators, which are created due to total internal reflection at an interface when a transparent spherical object traps light. Essentially, these have the ability to trap light within a small cavity.
Image Source: Fernan Federici
Researchers used these microresonators–along with optical gain materials, which transfer part of their energy to emissions in order to increase optical power–within biological cells. In doing so, this paper showed that in vitro cells can demonstrate optical functions such as lasing, or giving off light just as lasers do. First, researchers described WGM cavities; by injecting oil droplets into cells, they created an optical cavity into which fluorescent dye could be injected and light pulses could be used to excite the molecules of dye to emit light, much like a miniature laser. Additionally, they showed that adipocytes, or cells that naturally contain lipid droplets, could be utilized for laser oscillation. Finally, solid microspheres, which took the form of polystyrene beads, were used to form non-deformable, intracellular lasers.
The applications of being able to turn individual cells into tiny lasers are wide-reaching, especially since one of the authors, Matjaž Humar, was quoted as saying the process is “actually super-easy”. Precise labeling and monitoring of individual cells may assist us in following the progression of cancer, for example.
Feature Image Source: Lasers by Douglas Muth
