I wrote this previous post complaining that I had not seen biomedical nanobots in spite of predictions from prominent futurists.

A retraction is in place since I just read that a research group had succeeded in remote controlling  bacteria  to go in any desired direction (via H+ magazine, p 12):

To do this, Martel used bacteria that naturally contain magnetic particles. In nature, these particles help the bacteria navigate toward deeper water, away from oxygen. “Those nanoparticles form a chain a bit like a magnetic compass needle,” says Martel. But by changing the surrounding magnetic field using an extended set-up coupled to an MRI machine, Martel and his colleagues were able to make the bacteria propel themselves in any direction they wanted. -from here

How you control a (magnetizised) bacteria with MRI, is beyond me, but I guess this can count as a proof of principle nevertheless.

The medical-nanobot scenario just became much more likely.