A new class of bio-lasers using self-healing biological material as the active medium has been introduced with the demonstration of lasing from colonies of GFP-expressing Escherichia coli (E. coli) bacteria as reported by Malte C. Gather and Seok Hyun Yun from Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital. The genetically transformed bacteria E.coli of the BL21 strain are capable of synthesizing fluorescent protein therefore allowing replenishment of the optical gain material in response to photobleaching. Lasing was achieved with placement of a single bacteria colony, covered with drop of glycerol to reduce scattering of light at the cell wall interfaces, between two dielectric mirrors forming a Fabry–Perot-type laser cavity. Both authors previously reported generation of laser light from similar microlasers equipped with fluorescent protein solution or single mammalian cells expressing GFP as an active medium.

In all these experiments, including the current research by Gather and Yun considered here, lasing was achieved by using pulsed excitation light at 465 nm from an optical parametric oscillator. Gather and Yun imply that despite the increased pump energy threshold for lasing in bacteria, this active medium is more promising than those reported previously for future large-scale, self-sustained biological lasers because the genetic engineering is more robust and efficient for bacteria.

Observation of lasing from living microorganisms proves that the inherent scattering and absorption can be fully compensated by stimulated emission at light levels that are not harmful to the host organism. In the future, several possible developments and applications of such bio-lasers can be considered. Engineering of the stand-alone cellular laser with integrated nanocavity is very attractive, as it could find many applications in light-based therapeutics, diagnostics, and imaging. Another possibility includes altering bacteria colonies between random or ordered structures to change the optical gain and therefore the requirements for pumping energy and laser cavity configuration. Generally, the use of fluorescent proteins as a laser medium is very attractive, as these are biocompatible and bioabsorbable and therefore uniquely suited for generating stimulated emission and laser light from and within living organisms.

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