[SeaDragon]

In Prey, Michael Crichton's tale of nanotech gone awry, a swarm of light-sensitive nanoparticles swim through a human body, creating the ultimate medical imaging system.

An excellent read and quite scary when you think about it....

[RightWingAtheist]

Why scary? Already, we've been using chemical and radioactive tracers in medicine for some fifty-sixty years now, and this is no different. I once had to swallow a barium solution so that the doctor could look at my innards through an oscilloscope, and personally, I'd rather have those little robots implanted in me than swallow two large cups of what tasted like salty cake batter again.