Lasers have three core components. To build a laser, all you need is an initial source of light, a material that amplifies it, and a reflective cavity. The first such “living laser” was built at Harvard University in 2011 using glowing sea-creature proteins and active kidney tissue. Xudong (Sherman) Fan at the University of Michigan, Ann Arbor, and his colleagues used a dye called Indocyanine green (ICG), a fluorescent dye approved by FDA, for their blood laser. It’s fluorescent in near-infrared light and is already injected into the bloodstream for use in medical imaging. The researchers figured that if they could get it to glow, ICG would make a great light source for a new kind of living laser. “Without blood, just ICG, it doesn’t work at all,” Fan told New Scientist. In the initial experiments with ICG, the dye’s light was weak. However, as soon as the researchers mixed ICG into blood and exposed it to a conventional laser, they noticed a good, bright light, created when molecules of dye bound themselves to plasma proteins. In effect, the blood had become the second vital component of a laser. The team is carrying out more trials to zero in on the right reflective cavity before moving to the bloodstream. Fan sees gold nanoparticles as ideal for that job, which might be able to bounce the light beautifully without causing harm. “Eventually, we are trying to do it in the human body,” Fan said. He is confident of fluorescent infrared light working in the bloodstream that may enable a surgeon to precisely pinpoint a tumor during a guided surgery. However, the challenge is to make sure that the intensity of the light generated will be within safe limits, Fan told New Scientist. “You don’t want to burn the tissue.” Blood is not the only bizzare material that’s been used to make lasers. In the 1970s, two scientists made a laser using jelly, while back in 2011, a different group of researchers used a living kidney cell to amplify the light. The team published a report of their progress in the Optical Society of America Technical Digest. Source: University of Michigan