That idea goes back at least to science fiction writers in the 40s: Heinlein's "Waldo" where it scaled down to microsurgery, and another story by someone else t

That idea goes back at least to science fiction writers in the 40s: Heinlein's "Waldo" where it scaled down to microsurgery, and another story by someone else that I read as a kid -- that one had robots building smaller robots, ending in a kind of grey goo emergency that petered out because metal nanobots rusted faster than they replicated, or something vaguely along those lines.