But not all nanotechnologies are alike; the range of innovations encompassed under the umbrella of "nanotechnology" is even greater than the difference between "micro-scale" technologies such as antibiotics and printed circuits. Although some nanotechnology specialists may quibble, I tend to split the concept of nanotechnology into three general categories. There are differences in complexity between the categories, but more important are the differences in use.

Read on for a discussion of the various types of nanotechnologies, including examples pulled from research announcements made over the last day or two, along with examinations of both their possible benefits and their potential risks.

Nanomaterials are materials produced at a molecular scale, and generally integrated into macro-scale products. Typically, these materials have unusual properties due to their nano-structure, allowing them to perform functions that coarser, more traditional materials can't do as well -- or, sometimes, can't do at all. Carbon nanotubes are the best-known type of nanomaterial, and as a quick scan through the WorldChanging archives suggests, they have a staggering array of possible uses.

Another type of nanomaterial is known as a "quantum dot;" Quantum dots are tiny semiconducting crystals, with the potential to improve the capabilities and efficiency of a variety of light-related technologies, including solar power. Today brought the announcement that researchers at Rice University have figured out a way to make quantum dots that can cut their cost by 80 percent, from about $2,000 per gram to around $400 per gram. This, in turn, should greatly reduce the price of materials taking advantage of quantum dot integration.

Not all nanomaterials need to be integrated into macro-scale products to be useful. We've reported before about research projects using nanoparticles injected into tumors then illuminated with a laser, causing them to heat up and destroy the cancer cells. Nature reports from the EuroNanoForum 2005 conference that one of these projects, using iron nanoparticles and magnets, is entering human trials.

Nanomaterials have some potential drawbacks, largely in the realm of toxicity. Some research suggests that certain types of carbon nanotubes can cause health problems if inhaled; although the actual likelihood of environmental exposure to such particles is questionable, this remains an issue requiring additional study. As the Center for Responsible Nanotechnology's Mike Treder noted in a recent editorial, "candor about the risks plus openness about purposes and processes is the best way to avoid a backlash." To this end, the establishment of the Nano Risk and Benefit Database at Rice University is a very useful tool.

Nanomachines are quite a bit different from simple nanomaterials. These would be molecular-scale devices that can perform physical processes through the application of energy, often (but not always) in service of a macro-scale goal. Note the use of "would be" -- for the most part, nanomachines are part of the "real soon now" future. Researchers working on the construction of nanomachines remain focused on getting component parts working; putting the parts together to make functioning devices is still to come, at least for serious applications.

Today's announcement of a molecular construct able to move larger-than-atom-sized objects brings the "real soon now" future of nanomachines a great deal closer. From the press release:

...chemists at Edinburgh University have used light to stimulate man-made molecules to propel small droplets of liquid across flat surfaces and even up 12° slopes against the force of gravity. This is equivalent to tiny movements in a conventional machine raising objects to over twice the height of the world's tallest building.

This significant step could eventually lead to the development of artificial muscles that use molecular 'nano'-machines of this kind to help perform physical tasks. Nano-machines could also be used in 'smart' materials that change their properties (e.g. volume, viscosity, conductivity) in response to a stimulus. They could even control the movement of drugs around the body to the exact point where they are needed.

The BBC, as usual, has more details:

The tiny machines that coat the surface [of the liquid moved] are essentially rod-like structures with rings that, in their normal state, furiously jump up and down because of Brownian motion (the random movement of molecules caused by collisions with molecules around them).

But when these structures are stimulated by ultra-violet light, a chemical reaction takes place and the rings all go to one end, changing the nature of the surface under the blob from a repulsive one to an attractive one.

This dramatically alters the surface tension of the liquid droplet above and it begins to move - even up a slight incline.

Despite being largely still on the drawing board (or, more appropriately, CAD screen), nanomachines have been the dominant image of nanotechnology since the publication of Eric Drexler's The Engines of Creation back in 1986. Engines foresaw a day of nanomachines everywhere, building things, tearing things apart for recycling, cleaning our ovens and our blood vessels... and making more of themselves. This became the basis of a scary scenario where "replicating assemblers" go out of control, disassembling everything (people, plants, rocks -- everything) in order to make more nanomachines. The scenario had a name that bordered on the silly -- "Grey Goo" -- and it scared a lot of people. Fortunately, not only is Grey Goo essentially impossible, Drexler himself has more recently made it clear that free-floating assemblers are neither necessary nor efficient ways of bringing about the nano-future.

So what would be better?

Nanofactories, the third type of nanotechnology, are the current model for the application of advanced nanoengineering. Comprising trillions of specialized nanomachines locked down and working in concert, nanofactories (sometimes called "molecular fabricators") would be desktop appliances not unlike an ink-jet printer. Plug one into your computer, fire up your favorite molecular design application (Adobe Nanoshop, perhaps, or Microsoft Nano -- "you appear to be constructing a molecule, would you like help with that?"), and the tiny machines in the fabricator convert raw materials (the "ink") into perfectly-formed objects.

Molecular fabricators are even farther out than nanomachines, but that still means they could show up within the next ten to fifteen years. WorldChanging ally the Center for Responsible Nanotechnology has focused its attention on the requirements and implications of desktop assembly, and CRN make a compelling case that (a) it's a lot closer than most might expect, and (b) the impact will be a lot bigger than most might imagine.

Of the three types of nanotechnology (nanomaterials, nanomachines and nanofactories) it's this last that has by far the most disruptive potential, for both good and bad. For the most part, the possible dangers arising from nanomaterials and nanomachines are quite similar to environmental hazards with which we're already acquainted, such as toxic industrial particles and pathogens, and the remediation efforts that might be needed are likely to be familiar as well. The rise of molecular fabricators, conversely, would be much more disruptive because the changes nanofactories would enable wouldn't necessarily affect our health, but would radically affect our economy and society.

Consider what might happen as desktop nanofactories, able to build just about anything that can fit within them, become cheaper and more sophisticated (remember: nanotechnology has much more in common with electronics than with traditional production techniques, and is likely to be subject to an acceleration similar to Moore's Law). Economies dependent upon material production (of shoes, of utensils, eventually of electronic devices) find that they have fewer markets as more people are able to "print out" their own customized objects. Economies specializing in raw materials might see a boost at first, but would decline as well as designers figure out ways to use less-expensive, more-commonplace materials as feedstock, eventually even disassembling old objects, becoming the ultimate recycling system.

Consider what might happen if we start to apply the same kinds of intellectual property regimes to our products that we do to our music and movies.

Consider what might happen if advanced weapons were as easy to build with nanofactories as running shoes and cell phones.

Consider what might happen if everything we built with nanofactories consisted of materials with high-efficiency photovoltaic properties.

These and myriad other possibilities arise from a fabrication future. Fortunately, we are considering what might happen. Last month, the Center for Responsible Nanotechnology announced the formation of a Task Force to study societal implications of molecular fabrication. Members of the task force include technology specialists, futurists, environmental scientists, philosophers, and more, from around the world. I have the privilege of serving on this Task Force, and look forward to our ongoing discussions and investigations of the possibilities inherent to this form of nanotechnology.

The possible impact of molecular fabrication helps to make the next two decades highly uncertain, but also ranks as one of the chief reasons why a bright green future could remain possible even despite major setbacks. This is why we continue to watch closely for developments in nanotechnology. Nanoscale technologies, from nanomaterials to molecular factories, are very likely going to change the way we create, work and live. We all should be paying attention.