Sounds like something out of a Jules Verne story.
A team of researchers at Carnegie Mellon have released word of a micro-sized robot that they anticipate being able to swim through your veins. That sort of device can go where microscopes and needles can’t, giving doctors new opportunities to not only examine the inner workings of the body, but also deliver drugs to infection points with pinpoint precision.
The scientists got the idea for the propulsion system from watching the flagellum of e. coli bacteria. (Interesting use of a harmful organism as inspiration for a bacteria-hunting device, but hey, Michael Crichton wrote a whole novel based on this concept — Prey.)