We basically have nanobot's. The problem is unlike science fiction working at the atomic scale things don't react the same way. For example you can build a motor, but ATP or something close it it's going to be the fuel as heat engines don't really work. Which is why we end up using Bactria/viruses/plants/animals and simply overwrite their DNA. Granted we can get a lot better but don't expect anything to be both small and intelligent even the simplest chip is huge we compared to a virus.