NewScientist (28 July 2015, paywall) reports on the capabilities of an excited human cell:
[Matjaž] Humar and his colleagues developed three ways to get cells to emit visible light. The first involved injecting each one with a tiny oil droplet, forming an optical cavity which could be filled with fluorescent dye. Shining a light pulse on to the cavity excited the dye atoms into emitting light in a tightly focused beam. …
Tagging cells with fluorescent dyes is a common and relatively easy way for researchers to label cells by getting them to emit light, but this produces a relatively broad range of wavelengths, making it difficult to distinguish between differently tagged cells.
However laser light is characterised by having an extremely narrow range of wavelengths. That means it is theoretically possible, using these new techniques, to give every single cell in the human body a unique, identifiable laser signature, Humar says.
