Mutating phagocytes for use outside the body could create an entirely new threat.
Evans syndrome is a condition where white blood cells indiscriminately attack other cells, At present, it's a rare autoimmune disorder but making white blood cells more aggressive presents the possibility of them finding a way to survive in living organisms and a means of transfer too since we've opened up the possibility of them no longer needing a host. Murphy's law.
It would be a real redundancy in expense to fund this type of research when you can use the already existing means of disinfectant. We have mild disinfectant weak enough to wash your hands with and strong enough disinfectant to pickle even metal and everything in between that range
such finances could be instead chanelled to causes geared toward finding solutions to autoimune disorders and finding how they really operate
I do see merit however in this idea and found another way to achieve the same result without the drawbacks. An article by the International Journal of Biosensors and Bioelectronics could prove useful. It details the progress in the field of nanotechnology including bionanomotors. It's a very fascinating read.