17 January 2008
It Really Is A Small, Small World
By Domenick DiPasquale
The amazing potential of nanotechnology, the scientific process of creating materials and products that are molecular or even atomic in size, promises to revolutionize life in the future. Working at this infinitesimally small scale — where the basic unit of measurement, the nanometer, is one-billionth of a meter in size — requires innovative techniques to create, manipulate, and manufacture substances visible only through instruments such as the electron microscope. The thickness of a human hair or a sheet of paper according to the nanoscale, for example, is 100,000 nanometers. Nanotechnology already has practical applications in everything from clothing to sports equipment, and U.S. scientists and researchers are working to harness the technology for additional breakthroughs.
Space Flight
Since the dawn of the Space Age a half-century ago, the weight of rocket fuel needed to lift a payload into or beyond Earth orbit has been a major limitation on space flight. Research in two revolutionary techniques employing nanotechnology offers the promise of overcoming this barrier, although their practical application is still far in the future.
At first glance, a “space elevator” — a device that literally could lift a payload some 35,000 kilometers into space via a tether extending from the Earth’s surface to a satellite in geostationary orbit — sounds more like the stuff of science fiction than science. The technical hurdles in constructing such a space elevator would be immense, not least of all the need to manufacture a super-strong cable of such great length and strength.
Nanotechnology may hold the key for turning this concept into reality. Researchers are investigating the possibility of using carbon nanotubes — structures only a few nanometers in diameter but several thousand nanometers in length — to build this cable. Because the carbon atoms that form the nanotube exert extremely strong bonds on each other, a nanotube is 100 times stronger than steel. Naturally, immense engineering and scientific challenges remain in constructing any such cable out of nanotubes, but progress continues. A research team at Rice University in Houston, Texas, for example, has found that combining carbon nanotubes with sulfuric acid aligns the nanotubes in the same direction, thus giving additional strength. While a functioning space elevator based on nanotechnology is decades in the future, it holds the promise of dramatically reducing today’s extremely high cost of putting a payload into orbit — estimated by the National Aeronautics and Space Administration to be $22,000 per kilo — to perhaps just a few dollars per kilo.
The payload-to-fuel ratio likewise comes into play during interplanetary flights, given the immense distances a spacecraft traveling within the solar system must cover. Brian Gilchrist, an electrical engineer at the University of Michigan, has suggested using nanotechnology to create a spacecraft powered by an array of nanoscale engines, each firing a steady stream of electrically charged nanoparticles through microscopic thrusters to propel the spacecraft forward. Millions of these engines would be clustered together on a silicon wafer just a few square centimeters in size; several such wafers would be combined to create the spacecraft’s propulsion system. Although this system would not have enough thrust to power the spacecraft’s liftoff from Earth, once in the vacuum of space the nanoscale engines could gradually and efficiently accelerate the spacecraft across the solar system to its final destination.
Medicine
Biomedical applications of nanotechnology currently under development may herald a radical new approach to diagnosing and fighting disease. The key lies in the incredibly small size of nanoparticles — small enough to infiltrate bacteria or even viruses and attack these organisms from within.
At the Lawrence Livermore National Laboratory near San Francisco, scientists are studying how to construct nanoscale-sized molecules called “shals” (synthetic high-affinity ligands) that are custom designed to adhere to a specific site on the surface of a human cell. Although shals were first envisioned as a bioterrorism defense tool that would detect and neutralize such pathogens as anthrax, biochemists at Lawrence Livermore and the University of California-Davis Cancer Center soon conceived a much broader medical use for them. By constructing shals specifically designed to adhere to the unique receptor sites on the surface of a cancer cell’s proteins, scientists hope to employ a new weapon in the fight against cancer. When combined with a radioactive isotope or anticancer drug, shals would not only seek out but also destroy the target cancer cells by releasing these disease fighters directly into the tumor. Experimental work is already under way to investigate shals as a treatment for prostate cancer and non-Hodgkins lymphoma.
While such a nanotechnology-based approach against cancer is still in the development stage, some medical applications of nanotechnology are already here. A U.S. drug firm, Nucryst Pharmaceuticals, is producing medical coatings infused with nano-sized crystals of silver, an element that possesses antimicrobial properties. Medical dressings coated with these silver nanocrystals, which range in size from 1 to 100 nanometers, deliver a fast-acting and sustained release of silver ions into wounds to speed healing. The technology is already in use in burn centers throughout the United States. Nucryst believes that this nanocrystal-based technology also will be useful in treating other types of infection and inflammation.
Environmental Science
The utility of nanotechnology often lies in the fact that, at the nanoscale level, material can exhibit markedly different physical and/or chemical properties compared to the characteristics the same material possesses in larger size. Nanotechnology’s atom-sized dimension in and of itself also offers unique possibilities. Scientists are studying whether these nanoscale advantages can be employed to create a healthier environment.
Drinking water in many parts of the world is contaminated with toxic substances, including metals such as arsenic. Removing these contaminants requires not only sophisticated equipment but also a steady source of energy to power this equipment — both of which may be in short supply in much of the developing world. Researchers at Rice University are investigating a low-tech approach to this problem using nanocrystals of magnetite, a compound of iron and oxygen that can absorb arsenic. When these magnetite nanocrystals are added to a solution of arsenic-contaminated water, they combine with the arsenic. A simple magnet then pulls the arsenic-coated nanocrystals to the bottom of the solution, where they subsequently can be removed. The particular benefit of this technique is that it works with common, everyday magnets, whereas using larger particles of magnetite would require much more powerful magnets. This research offers a simple new approach to providing clean drinking water to populations living in remote areas.
Nanotechnology’s very size by itself opens up possibilities. At Lehigh University in Pennsylvania, environmental scientist Wei-xian Zhang has been studying the use of nanoscale iron particles to clean up soil and groundwater polluted by heavy metals, pesticides, and organic solvents. When these iron nanoparticles are injected via a slurry mix directly into a contaminated site, their size allows them to slip in between soil particles. As the iron nanoparticles oxidize, they break down chemical contaminants such as dioxins or PCBs into less toxic carbon compounds. Heavy metals such as lead and mercury are likewise rendered less harmful as the oxidation process reduces them to an insoluble form less likely to leach into groundwater. Tests have shown that contamination levels begin to drop dramatically around the injection site within 48 hours, and that the toxic pollution is all but eliminated within several weeks.
Energy
The convergence of several factors — the pressure that continuous growth in the world’s population and economy is exerting on traditional fossil fuels supplies, concern over global warming, and the sharp increase in the price of oil — is making the development of alternate energy sources ever more critical. Current U.S. research in nanotechnology offers intriguing leads that may revolutionize the extraction of energy from clean, renewable sources, in particular solar.
Scientists at Harvard University, for example, have developed solar cells from “nanowires” that are just 300 nanometers in diameter. As described by the periodical MIT Technology Review, such a solar cell has a core of crystalline silicon and several concentric layers of silicon with different electronic properties. Each layer performs the same function that the semiconductor layers in traditional solar cells do of absorbing light and capturing electrons to generate electricity. While these microscopic solar cells may first be used to power other nanodevices, eventually it may be possible to bundle them together in large numbers to replace conventional solar panels in use today. Obstacles to commercializing this technology remain, however; researchers will need to develop ways to produce these solar nanowires in a denser array than at present and to improve their present low level of efficiency (less than one-fifth that of conventional solar panels) at converting sunlight into electricity.
Some 35 kilometers away from Harvard in the old textile town of Lowell, Massachusetts, a private high-tech company named Konarka is taking a different approach to using nanotechnology for solar power. The company has invented a process to apply nanoscale-sized particles of the semiconducting chemical titanium dioxide to a plastic film that is then coated with a light-sensitive dye. When sunlight or even artificial indoor light strikes the dye, the titanium dioxide particles produce electricity. Although this technology is still in the developmental stage, Konarka envisions a multitude of practical applications for this flexible plastic solar cell strip where traditional, rigid photovoltaic panels are impractical. These power-generating strips could, for example, be wrapped around devices such as cell phones or laptop computers to recharge them, placed on structures of any kind (even tents) as stand-alone power generators, or even woven directly into clothing to provide the ultimate power on the go for personal consumer electronics.
Domenick DiPasquale is a freelance writer. He previously worked for 27 years as a foreign service officer with the U.S. Information Agency and the U.S. Department of State in Ghana, Kenya, Brazil, Bosnia, Singapore, and Slovenia.
The opinions expressed in this article do not necessarily reflect the views or policies of the U.S. government.
