Here in Michigan, researchers are looking at "how certain kinds of nanoparticles damage cell membranes — enough to cause cell death in some cases — and how the damage can be prevented." The answer is you don't just pump the stuff blindly into the body. You engineer them, or make the little beasts do what you want them to do. One researcher says, "Not only does engineering make them less harmful, but it also makes them better at what we want them to do. You don't lose anything; it's all a gain."
This is another example of the kinds of "mixed" nanotech messages being presented to the public. Like any new science, there will be a "breakthrough of the week" that may or may not conform to a particular political agenda. One day dendrimers can cure cancer, the next day they'll kill you and the next day they'll save your life again.
The answer, of course, is this is why it's called nano "technology," and not just nanoscale stuff. Size, alone, does not necessarily matter. In fact, size alone could be more dangerous -- just as anti-nanotech groups like the ETC Group have claimed. However, when you add the "technology," when you engineer them for a specific function, that's when you really see the benefit. This is especially true in nanobiotech.
In many cases, the mainstream media have picked up on studies in which researchers pump rats' lungs or fish's brains full of dumb nanomaterials, and bad things begin to happen. Receiving less attention are the followups in which these nanomaterials, when engineered for a specific purpose, could possibly not only fail to kill the poor rodents or other creatures, but actually help them get better and learn to play the piano.
OK. I'm kidding about the piano.
Nano Hazards: Exposure to minute particles harms lungs, circulatory system (Science News)