Read Present at the Future Online
Authors: Ira Flatow
One of the most important areas of nanotech research is “self-assembly”—finding ways to prompt atoms and molecules to put themselves together in useful ways, just the way living cells in your body do. Some researchers are working on ways to grow back broken bones or damaged nerve cells. Others are making tiny machines.
For medicine, one of nanotech’s biggest dreams is a real-life version of Fantastic Voyage, the classic science-fiction film in which a team of doctors shrinks themselves and travel in an equally tiny submarine through a patient’s bloodstream to remove a blood clot from his brain. Some researchers are working on tiny devices that could travel to a particular organ inside a patient’s body and perform repairs or deliver drugs directly to a cancerous tumor, sparing a patient from the painful side effects of chemotherapy. How is that tiny machine going to move?
LOCOMOTION, THE NANO WAY
“There’s an interesting controversy in nanotechnology as to what the best strategy is,” says George Whitesides, professor in the Department of Chemistry and Chemical Biology at Harvard and executive director of the National Space Society. “At the beginning, there was an idea that the way to think about nanotechnology was to look around at things like submarines or automobiles or motors, devices that work in a scale we’re familiar with, and then make them very, very small, changing their size by a factor of a million or maybe more. But the idea of actually building very small mechanical motors has a lot of problems. For example, it’s not clear how you power
them. Friction gets to be much more important at small scales. Things just don’t scale from large to small very well.”
So Whitesides turned to the ultimate nanotechnologist: nature itself. “Nature’s been at it for a while and has some pretty clever solutions, much, much cleverer than the ones that we can come up with right now. So why not use them? Biology is full of rotary motors, linear motors, pumps. Every time I look into the strategies that simple organisms use to sense their environment, I’m just amazed at their sophistication.”
To test the concept, he used a tiny, one-celled algae as a nanoscale tugboat. He and his team used chemistry to attach plastic beads to the outside of algae, which swim by beating their flagella in a movement that resembles the breaststroke. They’re also sensitive to light, so by shining light on the swimming algae, the researchers can guide them back and forth to where they want them to go.
Whitesides is also very interested in self-assembly, “the process by which some complex system puts itself together. The pieces come together of their own volition. You don’t have to reach in and cause them to do it. Every crystal does that. You and I are examples of something that no robot put together; we put ourselves together. Biology is the master of self-assembly.”
Nanotechnologists have succeeded in making some amazing, incredibly tiny working robots that combine artificial and living parts. One researcher uses DNA itself to make a mini-robot “walk.” Since even a tiny portion of heart muscle beats, another nanotechnologist has attached a heart muscle to a nanoparticle to power a tiny working machine. But so far, these wonderful living machines remain demonstrations that work in the laboratory, not in a physician’s office or a hospital—yet.
The day when medicine mimics science fiction is still quite a way off. Some predictions for nanotechnology are very unlikely to come true. For example, Smalley always pooh-poohed the notion of “molecular manufacturing”—a day some futurists foresee when all the
products we need will be made inexpensively by nanobots. Nanotechnology is very difficult because researchers can’t specialize—to be successful, they often have to be very well versed in several disciplines, such as engineering plus biology plus chemistry. How many people can be experts in all those fields at once?
THE DNA TRANSISTOR
Professor Uri Sivan, chief of nanotechnolgy at the Technion Israel Institute of Technology, has coaxed DNA into building transistors, the basic building blocks of all computers. “We use DNA molecules as a template to complete the assembly of this electronic device. It turns out that DNA and its related proteins can indeed build remarkable structures.” The DNA is not electrically active itself; it does not carry electric current or do any of the work. “Our strategy is to use the DNA and those related proteins and engineer them in such a way that they will assemble nonbiological materials for us, and those nonbiological materials are the materials that have the electronic functionality. So we were using [the DNA] to pick up a carbon nanotube that can serve as a transistor and localize it on a DNA template. And then in the second step, we used that template to grow conductive wires connecting the nanotubes.” The DNA assembles the carbon nanotubes into transistors. And then the wires are assembled, literally, on the backbone of the DNA. “We developed a number of years ago a metallization process by which we can coat DNA specifically, so metal grows only on DNA. Metal grows along the DNA template and contacts the nanotube.”
Sivan compares it to taking the blueprint, the DNA instructions for making a transistor, putting it into a test tube along with all the necessary electronic ingredients to build the transistors, shaking it up, and watching the finished product come out. The transistors assemble themselves. “The last step is [that] we just dip a silicon wafer in solution. We pull it out and we have billions of those transistors on the silicon wafer.” They act just as conventional transistors do.
“Our challenge is to go on to more and more complex structures. The crux of the matter is whether we’ll be able to invent ways to self-assemble large amounts of objects into something functional.”
VIRUSES TOO
While Sivan is working with DNA, Dr. Angela Belcher, professor of materials science and engineering and biological engineering at MIT, believes that she might be able to force nature to work with materials not normally found in the wild and convince organisms, such as viruses, to build devices that are foreign to them. She is working to manipulate “three different parts of a virus simultaneously to start building” the basic parts of a transistor. “What we’re doing is mimicking nature, like how an abalone grows calcium carbonate to grow a shell. We’re using viruses to grow any kind of material we’re interested in, and one kind of material [is] semiconductor materials.”
It’s a tedious process that starts with sifting through countless numbers of viruses, weeding out only those that have the right talent for the job of, say, building a wire. “We take a billion viruses and allow them to interact with the semiconductor material, and then only keep a couple of them that interact very well, and we throw the rest of them away. And any one that does interact, we keep evolving it to have better and better interaction. Then we can make billions and billions of viruses that can now grow that particular semiconductor wire. We breed them to make a wire that we’re interested in.”
So to create a wire, the virus would bridge two different metals. “We can actually manipulate many different proteins and many different genes on a single virus, so we can have one end of a virus grow one kind of material and another end of a virus grow or attach to another kind of material, all through this genetic selection and amplification. We pour in precursors and grow wire—it can be a metal wire or a semiconductor wire or a magnetic wire—just by throwing in precursor salts.
What happens to the virus once the wire is completed? “We can either burn off the virus at that point, just by increasing the temperature, or we can keep the virus around and recycle it and use it again.”
Why use viruses? Belcher says she can use many different organ
isms—she also uses yeast to grow materials—but she focuses on viruses because they “have this nice shape. They’re very long and thin.”
Letting nature self-assemble devices results in electronic devices with fewer errors, since the wires can form only in the right places. It also allows you to customize the exact dimensions of what you are trying to make, by manipulating the genetic code of the virus. You want it this long? This thick? This wide? How about this strong? Just jiggle the genetic code. As Belcher told OpenDOOR, the MIT alumni magazine, “My dream is to have a material that’s genetically controllable and genetically tunable. I’d like to have a DNA sequence that codes for the production of any kind of material you want. You want a solar cell, here’s the DNA sequence for it. You want a battery, here’s the DNA sequence for it.”
NOT TO FORGET BACTERIA
Not only can viruses be coaxed into building microscopic electrical parts; so can bacteria. The press release said it all: “A microbiologist discovers our planet is hardwired with electricity-producing bacteria.” In other words, scientists have found that under certain conditions, some common bacteria can sprout nanowires that conduct electricity. And with the Earth populated with more microbes than any other form of life, that’s a lot of nanonetworking.
“Earth appears to be hardwired,” is how Yuri Gorby, staff scientist at the U.S. Department of Energy’s Pacific Northwest National Laboratory put it. Gorby and his colleagues discovered that they could coax some microbes to transform toxic metals into sprouting microwires, called pilli, as small as 10 nanometers in diameter. These wires could be formed into bundles as wide as 150 nanometers. And many other bacteria, not in the toxic metals business, can also form these wires, such as microbes involved in photosynthesis and fermentation. But what they all have in common is the ability to reach out and touch other bacteria by growing these wires from their cell
membranes that find the other microbes and “form an electrically integrated community,” says Gorby.
Being electrically conductive means that the bacteria hold the potential (pun intended) to be the power sources for fuel cells and bacteria-powered batteries.
Why would nature make such bacteria that can produce and conduct electricity and have the power to clean up toxic metals? Gorby can only speculate.
“The effect is suggestive of a highly organized form of energy distribution among members of the oldest and most sustainable life forms on the planet.”
SAFETY
One question often asked is “How safe is nanotechnology?” What if all those tiny nanoparticles spill into our water supply? Or what if we were to breathe them in as they came out of an aerosol spray can or sprayer in the workplace? Right now, we don’t know, although we’re sure that self-replicating nanobots will never take over the Earth and reduce every living thing to “gray goo,” as computer scientist-entrepreneur Bill Joy has warned. Nor will we ever be stalked by intelligent, predatory nanobots, as hapless scientists were in Michael Crichton’s scary thriller, Prey. But many people, including some in the federal government, are concerned about the potential health hazards posed by these tiny particles that can easily get into the blood and be captured by the lungs.
“Major efforts are underway in both industry and government to realize the amazing promise of this technology. However, very little attention is devoted to assessment of health risks to humans or to the ecosystem,” says the National Institute of Environmental Health Sciences, part of the National Institutes of Health, in a 2003 report. “The toxicology of nanoparticles is poorly understood, as there is no regulatory requirement to test nanoparticles for health, safety, and environmental impacts. More research is urgently needed, as there are many indications that ultrafine particles could pose a human
health hazard. Research is now showing that when harmless bulk materials are made into ultrafine particles, they tend to become toxic. Generally, the smaller the particles, the more reactive and toxic are their effects.”
An animal study, reported in 2004 by the Society of Toxicology, compared the effects of different, common pollutants on the lungs of lab rats. It found that “if carbon nanotubes reach the lungs, they are much more toxic than carbon black and can be more toxic than quartz, which is considered a serious occupational health hazard in chronic inhalation exposures.” (Scientists were from NASA’s Johnson Space Center, Wyle Laboratories in Houston, and the University of Texas Medical School at Houston.)
“I don’t know that we can say that nanoparticles are inherently risky,” says Dr. Kristen Kulinowski, executive director of education and public policy at the Center for Biological and Environmental Nanotechnology and director of the International Council on Nanotechnology at Rice University in Houston, Texas. “What I would say is that the size and surface chemistry of nanoparticles raises concerns that they might have unique toxicological profiles that we don’t see in particles that are larger of the same chemical composition.”
In April 2006, the RAND Corporation released a report exploring health risks associated with the use of nanomaterials in the workplace. The report said that the U.S. government is providing insufficient funding to understand and manage risks that nanomaterials pose to the health of workers in the rapidly growing nanotechnology industry. The RAND report said that the government has directed more than a billion dollars annually to the development of nanotechnology, but just 1 percent of that, $10 million, to studying research understanding and managing the risks involved. Basically, that says there’s not enough money going into researching the health effects of nanotechnology. This is an issue that bears close watching.
THERE’S NO BUSINESS LIKE SPACE BUSINESS
Our goal is to solve, or help solve, what I consider to be, by far and away, the great problem of space, which is the cost of getting there.
—ELON MUSK
In 2004, President George W. Bush announced a new goal for the U.S. space program: return to the moon, and after that, aim for Mars. NASA administrator Michael Griffin said that the current space
shuttle program and International Space Station (ISS) were “not the right path” for the space agency after the highly successful Apollo moon missions of the ’70s.