Using nanomachines for a lot of the purposes that people come up with is ridiculous. It's like trying to make a tractor wrap a present....without a driver. How do you give a machine intelligence that a fully blown unit can't match, and make it agile and able to understand it's surroundings?
It's not possible. While we're at it why not make them out of the collapsed singularity from a black hole so we don't have to worry about the granularity of atoms.
Cleaning floors: Babies are excellent for that. Just give them a nice fluffy romper.
Killing pests: Babies again. They stomp on them and/or eat them. Or hammers, or pesticides.
A cool idea, but it's pure fantasy!
Sure, I've seen the little gears etc, but what use is a couple of tiny gears? Put them together and you get a larger machine.
Biotech is probably better. the hard work has already been done billions of years ago. Ie Making cells work etc.
I do like the tiny little gold toyota with the working electric motor though. That is seriously cool.
