Navigating the Nano Era: Challenges and Mysteries of Man-made Nanoparticles
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The use of man-made nanoparticles has spread into almost every area of our lives: food, clothing, medicine, shampoo, toothpaste, sunscreen, and thousands of other products. Regulatory structures, both here and abroad, are completely unprepared for this onslaught of nanoproducts, because nanoparticles don’t fit into traditional regulatory categories. Additionally, companies often shield details about them by labelling them “proprietary”; they’re difficult to detect; we don’t have protocols for judging their effects; and we haven’t even developed the right tools for tracking them.
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As with many things that are invisible and difficult to understand—think subatomic particles such as the Higgs boson, muons, gluons, or quarks—any discussion of nanoparticles quickly shifts into the realm of metaphor and analogy. People working in nanoscience seem to try to outdo each other with folksy explanations: Looking for a nanoparticle is like looking for a needle in the Grand Canyon when the canyon is filled with straw. If a nanoparticle were the size of a football, an actual football would be the size of New Zealand. A million nanoparticles could squeeze onto the period at the end of this sentence.
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Nanoparticles exist in nature, but they can also be manufactured. One way is top-down: grinding up things that are big until they are really, really small, an approach used in nanolithography for electronics. Or you can make them from the bottom up, following instructions that read like a chemistry textbook: mixing one chemical with another by pyrolysis (heating a material in a partial vacuum), or with electrolysis (running a current through a liquid), or by other means. But what do they look like? Like many dots of light that I’m reminded of staring up at the Milky Way on a trip across the Tibetan Plateau years ago. Yet the silver dots throb and undulate as if alive. Here and there, giant spheres of dust, as large as Goodyear blimps, porpoise through the nanoparticles. This world is so close—it’s even inside me—yet it looks so other, so mysterious.
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Scientists don’t really have a full theoretical foundation to explain reality at this scale. But all agree that one of the most important aspects of nanoparticles is that they are all surface. Consider a conventional chemical process: When one element is reacting with another, it’s really just the surface molecules that are involved in the lock-and-key dance of classical chemistry. The vast majority of the molecules remain interior, and stable. But there are many fewer molecules in a nanoparticle, so most of the molecules are on the outside, thus rendering nanoparticles more reactive. Myriad surface imperfections cause randomness to dominate the nano world. If you hit a billiard ball with a clean shot at the macro level, you can have a good idea where it will go. But at the nano level, a billiard ball might shoot straight up, or even reverse direction. These bits of matter are hot to trot: ready to react, to bond, and to do so in unpredictable ways. While man made nanoparticles have entered every area of our lives scientists are still to understand them, and regulatory authorities are unprepared to meet the challenge.
