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Thursday, Nov 26, 2009
These issues used to be of interest only to theoretical physicists and Zen Buddhists with a scientific streak. No longer. Nanotechnology will integrate quantum mechanics directly into industrial processes.
For example, check out the carbon nanotube, possibly the most famous nanostructure. There are numerous ways to build nanotubes. The one shown here looks like a cylinder, one of the standard three-dimensional structures we learned about in geometry, right? Wrong! Because it is only one atom thick, this nanotube is considered to have properties, distinct quantum features, that are one-dimensional! For example, this single-walled carbon nanotube (SWNT) can behave as an electrical conductor, a semiconductor or a nonconductor (insulator), depending on which way individual atoms are oriented relative to the axis of the tube. In the physical realm, that would be like saying we could change a cylinder of coiled copper wire from an electrical conductor to an insulator by wrapping it in the opposite direction. Because of this and many other unusual properties, SWNTs are expected to revolutionize the most important devices in our lives -- from nanoscale transistors for our computers to neuroelectronic splices to repair (or enhance) synaptic signaling in our nervous system.
Quantum dots (Q-dots) are another hot product in the nanotech pipeline that create value by dipping below the atomic surface. Small bits of matter, often only 10 to 50 atoms, Q-dots behave as the "supersized" equivalent of a single atom. Basically, they work by "confining" electrons so that they can no longer move and propagate as waves and particles (see above). They become pure waves, and their positions and velocities take on an uncertain, probabilistic nature. This quantum confinement causes the electrons to "freak out" and emit much more energy than they would if they could use both their wave and particle properties. This is quantum behavior conveniently packaged as a piece of primal material that we can handle and work with in the physical world.
Q-dots do a lot of cool things, but one of them truly defies everyday experience. When a dot is energetically excited, the fewer number of atoms in the dot, the higher the energy and intensity of its emitted light -- smaller is brighter. In this nanoworld Tiffany's, the 1/10-carat diamond is much brighter, and worth much more, than a 10-carat stone of equal cut and clarity.
One of the high-value medical applications of Q-dots is medical imaging. Because of their ability to produce very bright light while taking up almost no space, quantum dots are already being linked to antibodies and other "magic bullets" used to hunt metastasized cancer cells. Q-dot diagnostics may even be sensitive enough to decode the mutated DNA sequence of each cancer cell, a key goal of personalized medicine. The combination of nanoscale and extreme brightness means that, theoretically, no cell could hide from Q-dot therapy and, once tagged, the dot could act as a target for laser destruction of the cancerous renegade. Only a device that spans the quantum and Newtonian worlds could create these possibilities.
And that is exactly the point. By building with individual atoms, nanoengineers will incorporate quantum behavior into their devices. Just saying you work with stuff 100 nanometers or smaller doesn't begin to get that message across. Many protein molecules, and even a few viruses, break this size barrier. By defining nanotechnology as the set of tools necessary to design and build molecular devices with atomic precision, we explicitly recognize that nanoengineering will span both the physical and quantum worlds. Once we understand this, we understand why nanotechnology will ultimately change the way everything is made, including, as the White House said, "objects not yet imagined."
All this sounds wonderful. But unknown, perhaps catastrophic, dangers may lurk in this emerging future. There is already concern about the fate of nanoscale particles inside the body, both those placed there intentionally and others arriving through the environment. Will Q-dots or other nanoparticles introduced via medical procedures have unexpected side effects? Will they, for instance, cross the blood-brain barrier more readily than normal chemotherapy agents? And what about airborne particles? Given the upper size limit of 100 nanometers, our atmosphere is already full of naturally occurring and synthetic nanoparticles (so-called ultrafines). But industrial production of SWNTs will mean that we must safely handle tons of particles with exotic chemistries and physical properties never seen before on earth.
Then there are nanotechnology's vast military applications. The key area is biodefense, which is the top R&D priority of the federal government across all agencies, far exceeding research for all diseases combined.
Violating all signed biodefense treaties, the United States has built six new "biosafety level four" (BSL4) facilities with a combined square footage far beyond our wildest needs for anything that could possibly qualify as "defense" research. The reason is that "countermeasures" cannot be built without the "measures" to test them. We are threatening to ignite the next global arms race -- not to mention creating a stockpile of substances so horrific they can scarcely be imagined -- by planning to manufacture fourth-generation recombinant DNA bioweapons, nano-enable them, and test them. As per Bush's usual M.O., there has been no consultation with anybody.
Finally, and most disturbingly of all, are the ethical issues involving subatomic manipulation of the human body. How does one draw the line between a justifiable intervention to save lives and a hubristic disruption of what it means to be human? Are we humans even capable of wielding that much power wisely? Are we in danger of engineering ourselves into a whole new species?
If nanotechnology offers to bring quantum benefits to our lives, then we must assume there will also be risks beyond the realm of our experience and imagination. Some of the deep things in science are not found; rather they are unleashed by the search itself. And they may not be our friends.
