This still has massive hurdles. If you're going to have nanobots running around in your bloodstream, you need to protect them from the immune system. Worst case

This still has massive hurdles. If you're going to have nanobots running around in your bloodstream, you need to protect them from the immune system. Worst case, you might have a massive immune response against the nanobots that causes a person to go into anaphylaxis. Somehow, you have to make them biologically inert without affecting our ability to control them or have them work. There is some success using antibodies to deliver targeted therapies to certain organs, but in general, this drug delivery is a very hard problem. If we were able to solve it, then we would easily cure cancer. There are tons of chemicals that are toxic to the body as a whole, but would work great if you could narrowly target to the tissue or cells of interest.