Biotechnology is advancing so that we can map the molecular structure of viruses and modify them, e.g., to make vaccines. However, this same technology will give us the ability to change these viruses, in manmade, technological ways. This gives us the technical power to make a virus which would kill every human on Earth, e.g., a variation of the AIDS or Ebola virus which spreads as easily as the common cold, reproduces much faster, and is more effective in killing its host. There are many species that have come into existence on this planet and which are suspected of having become extinct due to a natural virus outbreak within the species. A manmade virus could be far worse than a naturally occuring one.
Nanotechnology is the ability to manipulate matter at the molecular level.
Biotechnology is a kind of nanotechnology. There are other kinds of nanotechnology. There are also concepts for molecular machines in manufacturing whereby they convert material in the environment without being consumed themself, like a regular factory, but these machines are microscopic. We would see our biosphere, ourselves, and those we love die. Perhaps in 20 years.