Buckyballs, Nanotubes, DNA, and Micromachines: Building Blocks of Nanotech
Nanotechnology is a field that’s just being established, and although there are big plans for the smallest of technologies, right now, most of what nanotechnologists have accomplished falls into three categories: new materials—usually chemicals—made by assembling atoms in new ways; new tools to make those materials; and the beginnings of tiny molecular machines.
A buckyball. Source: Office of Basic Energy Science/U.S Dept. of Energy.
Some of the primary building blocks in nanotechnology are buckminsterfullerenes (almost always known as buckyballs or fullerenes), which are clumps of molecules that look like soccer balls. In 1984 Richard Smalley, Robert Curl, and Harold Kroto were investigating an amazing molecule consisting of 60 linked atoms of carbon. Smalley worked these atoms into shapes he called “fullerenes,” a name based on architect Buckminster Fuller’s “geodesic” domes of the 1930s and first suggested by Japan’s Eiji Osawa. Sumio Iijima, Smalley, and others found similar structures in the form of tubes, and found that fullerenes had unique chemical and electrical properties. Fullerenes became nanotech’s first major new material. But what to do with them? Engineers turned their attention to finding some practical use for these interesting molecules.
The letters “IBM” spelled in xenon atoms, as imaged by the atomic force microscope. Courtesy: IBM.
While engineers thought about practical uses for fullerenes another discovery in search of an application was being made. In 1981 Gerd Karl Binnig and Heinrich Rohrer invented the scanning tunneling microscope or STM, which has a tiny tip so sensitive that it can in effect “feel” the surface of a single atom. It then sends information about the surface to a computer that reconstructs an image of the atomic surface on a display screen. If that weren’t amazing enough, a little later, researchers discovered that the tip of the STM could actually move atoms around, and Donald Eigler and a team at IBM staged a dramatic demonstration of this new ability, spelling out "IBM". Researchers believed they had a tool, the atomic force microscope (AFM), that could build things atom-by-atom. But, like the discovery of fullerenes, it remained to be seen if anything useful could actually be built this way.
The development of tools such as AFMs coincided with the introduction of very powerful new computers and software that scientists could use to simulate and visualize chemical reactions or “build” virtual atoms and molecules. This was especially useful for scientists working with complex chemical molecules, particularly DNA. Researchers recognized that the actions of DNA resembled some of the things nanotechnologists were now calling for—the use of molecules to construct other molecules, the self-replication of molecules, and the use of molecule-size mechanical devices. Perhaps DNA (or its cousin, RNA) could be modified to create the first nanomachines?
Ned Seeman has succeeded in manipulating strands of DNA into customized molecules with multiple interconnections. He believes this is the first step in doing more complex things with DNA, such as using it to create molecular machinery. Source: NYU.
Geneticists had already found ways to use DNA taken from bacteria to make a nano-scale replicator used for scientific research. By modifying some of the chemical reactions that take place in natural DNA, genetic engineers had figured out a way to make copies of nearly any DNA molecule they wanted to study. But with the computers and tools available to them by the 1990s, they began using DNA or DNA-like molecules to do other things—like construct new chemicals or tiny machines. Many researchers began investigating ways to make proteins—the components from which DNA is made—that would perform useful tasks, such as interacting with other materials or living cells to create new materials or perhaps attack diseases. One of the first breakthroughs was Professor Nadrian Seeman’s demonstration of a tiny “robot arm” made from modified DNA. While the arm could not yet really do anything useful, it did demonstrate the concept.
An experimental MEMS micro-gyroscope developed at the Georgia Institute of Technology.
Meanwhile, electronics researchers approached nanotechnology from another direction. Since 1959, engineers had etched and coated silicon chips using a variety of processes to make integrated circuits (ICs). The transistors and other chip elements reached nano-scale in the late 1990s. They also used these same techniques to develop the first micromachines—microscopic devices with actual moving parts. Some of the early versions of these were simply intended to demonstrate the process without doing anything particularly useful, such as a tiny guitar with a string that could be plucked using an atomic force microscope. But in the late 1980s these began to be commercialized as machines-on-a-chip, or micro-electrco-mechanical systems (MEMs), which combine ICs and tiny mechanical elements. However useful MEMs are, most engineers feel that the techniques used to make ordinary ICs will never be refined enough to make true nanotechnologies. For that reason, engineers are now concentrating on discovering entirely new ways to make ICs, building them from the ground up rather than cutting and etching “bulk” silicon slices.
With the appearance of protein-based chemistry and other techniques in the 1990s, researchers began looking both for practical uses for nanotechnology and new ways to make nano-molecules or micromachines. A different but related problem was that of making nanomolecules in large numbers. A single nanomachine or nanocircuit for example, would not be able to do enough work to make a difference in the real world—thousands or millions might be needed. Engineers needed ways to turn out their nanomachines in huge numbers, and so they began looking for a way to make a nano-scale machine or molecule that would assemble other nano-scale machines or molecules. K. Eric Drexler called it a “self assembler,” and scientists believe that it will be one of the keys to making certain kinds of nanotechnology useful and practical. To date, very few practical nanotechnologies and no self-assemblers have been used outside the laboratory.