NANOTECH INNOVATIONS

On the distant horizon is molecular nanotechnology, literally the organization of matter at molecular scales. Imagine, for example, “smart” clothing, in which the molecules comprising the fabric can change in response to weather. The idea, as sketched by the late Richard Feynman at a meeting of the American Physical Society at Caltech in 1959 and elaborated on later by many others, is to enable the manipulation of individual atoms and molecules, using proportionally smaller tools to build and operate even smaller tools.

Biological systems are the perfect models for molecular nanotechnology, inspiring future nanotechnology. The capabilities of biological systems put present technology to shame.

Although nanotechnology is often relegated to the field of materials science, by taking a closer look at biological systems, it could one day have a profound effect on the earth sciences. In particular, millennia-old notions of what a “resource” is, and the collection and use of energy, are both likely to change beyond recognition.

Fuel laws

Current technology squanders energy because most of it is used as heat. Indeed, we could speak of the “heat” crisis rather than the “energy” crisis. Fuels, after all, are burned! Two-thirds of gas in an automobile’s tank, for example, goes right out the radiator. Due to the Carnot limit, a law that stems directly from fundamental constraints imposed by thermodynamics, even the most efficient heat engines waste at least half the applied energy.

Because electric batteries and motors are not heat engines, they are not subject to the Carnot limit, making them much more efficient. Conventional batteries, however, have other engineering issues such as low energy density and slow recharge times. Instead, fuel cells are a promising alternative.

While similar to a battery, fuel cells allow for continuous replenishment of the reactants consumed — producing electricity from an external supply of fuel and oxygen as opposed to relying on the limited energy storage capacity of a battery. And contrary to popular belief, fuel cells do not necessarily require hydrogen.

Practical fuel cells using, say, hydrocarbons or alcohols lie beyond present technological capabilities, as converting the chemical energy of fuels directly into electricity requires a highly controlled molecular-scale reaction. This process requires catalysts that are both extremely specific and robust, and hence well structured at the nanoscale. Better catalysts in general are an obvious application of near-term nanotechnology, and will have further profound and ramifying effects on energy efficiency.

Another near-term nanotechnology solution involves solar energy. It is often claimed that the high energy density of conventional fuels is not reproducible by any conceivable alternatives, at least at the scale required for modern civilization. But the high energy density of conventional fuels is merely a brute-force solution that is compensating for the inefficiency of burning them. Thus, it is simply not true that solar power is incapable of powering a technological culture.

A high-tech culture is the only sort that can be run on solar power. After all, life itself, with its extraordinary capabilities of self-organization, synthesis and element separation, runs on solar power. That’s why it is amusing to consider, for example, the oft-proposed use of biomass for fuel: Burning material originally assembled, atom by atom, from diffuse sources of both energy and materials.

Artificial photosynthesis

Why is solar power usually thought to involve converting sunlight into electricity? Biology doesn’t do it that way. Natural photosynthesis stores the energy of sunlight in chemical bonds. That makes a lot more sense biologically, as well as technologically.

The conventional disadvantages of solar power are that it is intermittent, and difficult to transport and store. The last two disadvantages are true of electricity, no matter how it is created. Using sunlight to make fuels, however, would solve the intermittency problem: Fuel can accumulate whenever the sun is shining and then be used later when needed.

Acidic drainage from mines is a pollution problem that could one day be a potential resource, by using nanotechnology to separate valuable minerals and dispose of contaminants. Photo is courtesy of Stephen L. Gillett.

Artificial photosynthesis is now receiving much attention by industry and research groups. The most promising approaches are based on semiconductors — materials for controlling conductivity that make possible most of modern-day electronics, including computer chips and lasers.

As in a conventional photovoltaic (solar) cell, semiconducting materials, such as silicon, absorb solar radiation. That radiation knocks electrons loose to create a flow of current, and each excited electron leaves behind a vacancy, or “hole,” that acts like a single positive charge. Conventionally, the electrons and holes are forced to drive an electric circuit before they recombine. Instead of driving an external circuit, however, technical alterations can make the hole and electron drive chemical reactions that store energy.

Most research has focused on “water splitting,” the production of hydrogen gas from water, but alternative fuel generation is possible. Familiar semiconductors, such as silicon, are too vulnerable to oxidation reactions to be used in such photochemical applications. Work instead has focused on oxide semiconductors, such as titanium dioxide, which remain stable indefinitely in an oxygen-water environment. Reaction takes place at the wetted interface between the water and semiconductor.

To be practical, however, such semiconductor surfaces will require near-molecular-scale structuring. Because the electrons and holes can combine to form heat, nanostructuring of the surface is necessary to ensure reasonable charge separation. At present, “decorating” the surface with nanoparticles of a precious metal, such as platinum, is the favored method of ensuring charge separation, but obviously this increases both expense and complexity.

An ironic result of such technologies is that desert areas, with their year-round sunlight, could become major fuel production centers. In particular, the nations of the Middle East could continue exporting fuel indefinitely, albeit in competition with other deserts throughout the world.

Pollutant v. Resource

A fundamental technical problem involves separating one kind of atom or molecule from a background of others: pollutants from wastewater, metals from ores, salt from seawater. Separation is basic to purification, pollution control and resource extraction. Defining the process is a question of context: If we want what we separated, it is a resource; otherwise it is a pollutant.

Traditionally, however, separation has been viewed as the source of a host of different problems. In particular, researchers have seen resource extraction not only as distinct from pollution control, but also as intrinsically energy-intensive. In turn, its profligate energy usage is typically justified by vague appeals to the laws of thermodynamics.

Yet, quantitatively, element separation is not intrinsically expensive. Do not merely believe thermodynamic calculations: Bio-logical systems underscore how woefully inefficient conventional separation processes are, as they perform feats that put conventional resource extraction to shame.

Organisms do not carry out thermally driven phase separation. Instead, they literally move individual atoms or molecules, using specialized mechanisms — for example the binding of nutrient elements by specialized proteins. These molecular-scale processes are vastly less costly energetically and allow separation from considerably lower concentrations.

Plant roots extract both nutrients and water at low concentrations from the ambient soil. Vertebrate kidneys extract only certain solutes out of the blood from a background of many other solutes. For photosynthesis, plants extract carbon dioxide from the air, where its concentration is only about 350 parts per million, and furthermore do so using only the diffuse and intermittent energy of sunlight. Diatoms are particularly impressive, building shells from silica extracted at parts-per-million levels from the ambient water.

Organic compounds called “crown ethers,” shown here schematically, could be key players in nanotechnology designed to extract metals. The ring, or “crown,” changes in structure by substituting differently sized atoms, such as potassium or lithium, for oxygen in the crown. Image is courtesy of Stephen L. Gillett.

Again, the reason why conventional resource extraction is so energy expensive is because it largely relies on vast quantities of heat, in this case to drive the partitioning of elements into coexisting phases. Not only do such processes require a lot of energy, but they also are intrinsically polluting, both due to the combustion necessary to generate the heat and because the separation is never complete. Moreover, byproducts containing geochemically abundant elements, such as iron in copper ores, are usually uneconomic and discarded as waste.

Thermal-based separation is also impractical for pollution control and purification. Of course, that’s why such problems are traditionally viewed as distinct from resource extraction. Indeed, a number of embryonic molecular separation technologies already exist whose development has largely been driven by addressing purification issues.

Extracting solutions

In their simplest form, molecular separation techniques require that the material being separated be free to flow as a gas or a liquid. Selectivity of the separation is also fundamental: Usually only one particular dissolved species is of interest, but it is dispersed in a background of many others. Sometimes the species is valuable (for example, palladium and lithium), whereas in other cases it is toxic (for example, lead and cadmium).

One particular set of approaches toward selective molecular separation has been the focus of a tremendous amount of research in recent decades. Such efforts involve molecules with branched and ring structures that can bind tightly and specifically only with certain solutes. For instance, a group of organic molecules called crown ethers are highly effective extraction agents for many metal ions.

Crown ethers are strongly selective. The ring, or “crown,” changes in structure by substituting differently sized atoms, such as nitrogen and sulfur, for oxygen in the crown. For example, the crown ether 18-crown-6 forms a strong complex with the potassium ion, which fits nicely into the ring, whereas the smaller ring of 12-crown-4 strongly binds with the lithium ion, but is too small to accommodate potassium.

One application of such a separation system is to tether the extraction agent to a substrate to form a highly selective surface for extracting particular solutes from solution. For example, researchers have used a substituted crown ether tethered to a silica surface to recover palladium from scrap catalytic converters dissolved in acid. The palladium is bound, while the other much more abundant metals remain in solution.

The major problem with such approaches to separation is that eventually the solute must release its captured ions to regenerate the extraction agent. Typically this takes extreme chemical measures. In the palladium recovery system, for example, highly concentrated acid must be used to flush out the palladium.

Such steps generate a much larger volume of wastewater that now becomes a serious disposal problem. Separation requiring washing with fluids can be practical for recovery of highly valuable commodities like palladium, but its applications are obviously limited.

So-called switchable binding provides a way to solve the problem: Under one set of circumstances, binding occurs, but changing some variable causes the solute to unbind again. Again, biology has anticipated technology. Hemoglobin, for example, binds strongly to oxygen in the lungs, but under different chemical conditions elsewhere in the body, it gives up the oxygen to the tissues.

An example of switchable binding is “electrosorption,” which is based on straightforward principles of attraction and repulsion. Charging an electrode attracts ions with the opposite charge; reversing the charge of the electrode desorbs the ions again. Although first proposed in the 1960s for desalination, electrosorption remained impractical until the recent advent of nanostructured electrodes with very high surface areas. Because the “filled up” electrodes look like a charged capacitor, too, a great deal of the electrical energy can be recovered when the ions are desorbed.

More selective approaches require more molecular-scale structuring. For example, researchers have patented a process for extracting lithium ion from brine that uses electrodes made of a form of crystalline manganese dioxide. In the process, the electrode becomes negative, which leaves the crystal with an overall negative charge, so positive lithium cations are drawn into tunnels in the structure to compensate. Lithium cations can fit into these tunnels, whereas larger cations cannot. Reversing the charge on the manganese dioxide electrode then expels the lithium.

A similar system for extracting cesium ion is based on cesium nickel hexacyanoferrate. Here, the crystal structure contains large cavities that can accommodate the big cesium ion. Again, on applying a negative voltage, cesium cations are drawn in to compensate. The system is of great interest for extracting highly radioactive cesium-137 from nuclear waste.

An alternative potential trigger for switching binding is light. One way is to use molecules that change their structure upon absorbing a photon. The “backbone” of spiropyrans, a specialized class of molecules, for example, rearranges so drastically that a solution containing the molecule actually changes color when illuminated. Strategically arranging the extracting groups on the backbone can make the molecule go from binding solutes in its ground state to releasing them upon illumination.

A different approach uses the absorption of light by a semiconductor surface, but such systems are nascent. In this case, the photogenerated electric charge would drive molecular mechanisms at the surface. For example, a surface might adsorb ions from a solution in the dark, but desorb those ions when illuminated. Merely shining sunlight on a surface to desorb its solutes would obviously be much cleaner and “greener” than flushing it with strong acid solutions!

Blurring the lines

At present, pollution control and purification are the key economic drivers for these separation technologies. As they mature, however, they will blur the distinction between a “pollutant” and a “resource.” Moreover, recovered pollutants will begin to have an impact on resource extraction. After all, copper extracted from a wastewater stream is copper that does not have to be mined.

Ultimately, a great many aqueous solutions, of both natural and artificial origin, will become nontraditional resources. Wastewater streams, acid-mine drainage, seawater, concentrated natural brines such as those in oilfields or saline lakes — sometimes viewed now as problems — all could become potential sources of materials with the help of nanotechnology. 

Australian researchers have made a new material that could revolutionise the electronics market with thinner, faster and lighter gadgets.

Others are using nano-inspired technology to detect cancers, deliver drugs into the bloodstream, explore for oil and gas in an environmentally friendly way, enhance security, purify water and make prosthetics.

Who knows what they could do next?

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Australian researchers want to remain among the world leaders of innovation and to snare a hefty share of the global nanotechnology product market that's tipped to be worth $3 trillion by 2020.

Nanotechnology has become a priority area for development and funding in many nations, including China.

And the sector appears to offer endless opportunities for different fields to team up to exploit the fact that seemingly stable materials develop weird and wonderful properties in the nano form.

Gold, for example, has scientists excited and not for its more than $US1600 an ounce price tag.

RMIT University's Deputy Pro Vice-Chancellor (International) Suresh Bhargava says for centuries gold has been defined as a noble metal, or a stable one that's resistant to corrosion and oxidisation.

"But the same metal, when it comes to nano forms, is full of fantastic properties," Professor Bhargava says.

Nano sizes can be easier to comprehend when people realise a human hair is about 80,000 times bigger than a nano particle, the molecular biologist says.

One of Prof Bhargava's projects is using nano-engineered flecks of gold in a sensor to attract and measure one of the world's most poisonous air pollution substances, mercury.

"Mercury is a very toxic element. Sixty thousand babies in the US alone are born each year with mercury-related diseases," he says.

The sensor is almost ready for commercialisation and they are also working on ways to remove the toxic element from the air.

"It is not far away," he told AAP this week.

Australian researchers are also making waves in electronics.

They announced on Friday, in the journal Advanced Materials, they had developed a new two-dimensional material made up of layers of crystal known as molybdenum oxides, with properties that encourage the free flow of electrons at ultra-high speeds.

This could boost speed of communication and capacitance - the ability to store an electrical charge in a small chip.

One of the team, CSIRO's Serge Zhuiykov, says the importance of the new discovery will mean they'll be able to transfer data more quickly, and the functionality of devices will improve.

"At the moment it is beyond our imagination where this new material could be applied, but it could be employed to create thinner mobile phones, new types of flexible electronics or lighter laptops," he said.

Prof Bhargava says nanotechnology is being exploited by a raft of industries including oil and gas exploration, where a lot of sensors are required.

"It can become more cost effective, more environmentally friendly, it is 21st century exploration," he said.

But one of the biggest hurdles to making the most of innovation in nanotechnology in Australia is getting support for multidisciplinary research through project funding, resourced networking and research infrastructure.

Vipul Bansal, of RMIT's School of Applied Sciences, is working on a nanochip biosensor for malaria and other diseases.

He is also using nanoparticles as drug delivery vehicles and working with cancer researchers to improve detection imaging.

"The biggest challenge is lack of opportunity for biological scientists and material scientists to work together," Dr Bansal said.

People who work on the interface of medical and material sciences can't have research funded by the two main commonwealth funding bodies - the Australian Research Council and the National Health and Medical Research Council, he said.

"Commonwealth money is used but they don't work together, which is a shame," he said.

Prof Bhargava says competition for funding can impede co-operation.

"Instead of competing in the same area, when the market and the funding is getting very short, do it in a complementary way," he says.

Late last year the Australian Academy of Science's National Nanotechnology Research Strategy was launched with a warning that economies and industries that failed to invest in nano-inspired technology could be left behind as products with improved or new functionality replaced the old.

The national strategy called for industry, academia and government to form an alliance to maximise the potential economic, social and environmental gains made possible through nanotechnology.

Building complex products atom by atom with advanced nanotechnology: if and when this is accomplished, the resulting applications could radically transform many areas of human endeavor.

Products are manufactured in our modern industrial society for a variety of purposes, including transportation, recreation, communication, medical care, basic needs, military support, and environmental monitoring, among others. In this column I'll consider products in each category in order to convey a sense of the extent to which the early stages of the nanotech "revolution" could be limited by practical design problems, and to explore how those impacts, while limited, may still be quite profound.

Molecular manufacturing (MM) will be able to build a wide variety of products -- but only if their designs can be specified. If we know what kind of product we want and only need to enter the design into a CAD program, then certain nanofactory-built products may be relatively easy to design Extremely dense functionality, strong materials, integrated computers and sensors, and inexpensive full-product rapid prototyping will combine to make product design easier.

However, there are several reasons why the design of other products may be difficult. Requirements for backward compatibility, advanced requirements, complex or poorly understood environments, regulations, and lack of imagination are only a few of the reasons why a broad range of nanofactory products will be difficult to get right. Some applications will be a lot easier than others. So, let's look at what can -- and what can't -- be expected in the early stages of the "next industrial revlution."

Transportation is simple in concept: merely move objects or people from one place to another place. Efficient and effective transportation is quite a bit more difficult. Any new transportation system needs to be safe, efficient, rapid, and compatible with a wide range of existing systems. If it travels on roads, it will need to comply with a massive pile of regulations. If it uses installed pathways (future versions of train tracks), space will have to be set aside for right-of-ways. If it flies, it will have to be extremely safe to reassure those using it and avoid protest from those underneath.

Despite these problems, MM could produce fairly rapid improvements in transportation. There would be nothing necessarily difficult about designing a nanofactory-built automobile that exceeded all existing standards. It would be very cheap to build, and fairly efficient to operate -- although air resistance would still require a lot of fuel. Existing airplanes also could be replaced by nanofactory-built versions, once they were demonstrated to be safe. In both cases, a great deal of weight could be saved, because the motors would be many orders of magnitude smaller and lighter, and the materials would be perhaps 100 times as strong. Low-friction skins and other advances would follow shortly.

Molecular manufacturing could revolutionize access to space. Today's rockets can barely get there; they spend a lot of energy just getting through the atmosphere, and are not as efficient as they could be. The most efficient rocket nozzle varies as atmospheric pressure decreases, but no one has built a variable-nozzle rocket. Far more efficient, of course, would be to use an airplane to climb above most of the atmosphere, as Burt Rutan did to win the X Prize. But this has never been an option for large rockets. Another problem is that the cost of building rockets is astronomical: they are basically hand-built, and they must use advanced technology to minimize weight. This has caused rocketry to advance very slowly. A single test of a new propulsion concept may cost hundreds of millions of dollars.

When it becomes possible to build rockets with automated factories and materials ten times as strong and light as today's, rockets will become cheap enough to test by the dozen. Early advances could include disposable airplane components to reduce fuel requirements; far less weight required to keep a human alive in space; and far better instrumentation on test flights -- instrumentation built into the material itself -- making it easier and faster to determine the cause of failures. It seems likely that the cost of owning and operating a small orbital rocket might be no more than the cost of owning a light airplane today. Getting into space easily, cheaply, and efficiently will allow rapid development of new technologies like high-powered ion drives and solar sails. However, all this will rely on fairly advanced engineering -- not only for the advanced propulsion concepts, but also simply for the ability to move through the atmosphere quickly without burning up.

Recreation is typically an early beneficiary of inventiveness and new technology. Because many sports involve humans interacting directly with simple objects, advances in materials can lead to rapid improvements in products. Some of the earliest products of nanoscale technologies (non-MM nanotechnology) include tennis rackets and golf balls, and such things will quickly be replaced by nano-built versions. But there are other forms of recreation as well. Video games and television absorb a huge percentage of people's time. Better output devices and faster computers will quickly make it possible to provide users with a near-reality level of artificial visual and auditory stimulus. However, even this relatively simple application may be slowed by the need for interoperability: high-definition television has suffered substantial delays for this reason.

A third category of recreation is neurotechnology, usually in the form of drugs such as alcohol and cocaine. The ability to build devices smaller than cells implies the possibility of more direct forms of neurotechnology. However, safe and legal uses of this are likely to be quite slow to develop. Even illegal uses may be slowed by a lack of imagination and understanding of the brain and the mind. A more mundane problem is that early MM may be able to fabricate only a very limited set of molecules, which likely will not include neurotransmitters.

Medical care will be a key beneficiary of molecular manufacturing. Although the human body and brain are awesomely complex, MM will lead to rapid improvement in the treatment of many diseases, and before long will be able to treat almost every disease, including most or all causes of aging. The first aspect of medicine to benefit may be minimally invasive tests. These would carry little risk, especially if key results were verified by existing tests until the new technology were proved. Even with a conservative approach, inexpensive continuous screening for a thousand different biochemicals could give doctors early indications of disease. (Although early MM may not be able to build a wide range of chemicals, it will be able to build detectors for many of them.) Such monitoring also could reduce the consequences of diseases inadvertently caused by medical treatment by catching the problem earlier.

With full-spectrum continuous monitoring of the body's state of health, doctors would be able to be simultaneously more aggressive and safer in applying treatments. Individual, even experimental approaches could be applied to diseases. Being able to trace the chemical workings of a disease would also help in developing more efficient treatments for it. Of course, surgical tools could become far more delicate and precise; for example, a scalpel could be designed to monitor the type and state of tissue it was cutting through. Today, in advanced arthroscopic surgery, simple surgical tools are inserted through holes the size of a finger; a nano-built surgical robot with far more functionality could be built into a device the width of an acupuncture needle.

In the United States today, medical care is highly regulated, and useful treatments are often delayed by many years. Once the technology becomes available to perform continuous monitoring and safe experimental treatments, either this regulatory system will change, or the U.S. will fall hopelessly behind other countries. Medical technologies that will be hugely popular with individuals but may be opposed by some policy makers, including anti-aging, pro-pleasure, and reproductive technologies, will probably be developed and commercialized elsewhere.

Basic needs, in the sense of food, water, clothing, shelter, and so on, will be easy to provide with even minimal effort. All of these necessities, except food, can be supplied with simple equipment and structures that require little innovation to develop. Although directly manufacturing food will not be so simple, it will be easy to design and create greenhouses, tanks, and machinery for growing food with high efficiency and relatively little labor. The main limitation here is that without cleverness applied to background information, system development will be delayed by having to wait for many growing cycles. For this reason, systems that incubate separated cells (whether plant, animal, or algae) may be developed more quickly than systems that grow whole plants.

The environment already is being impacted as a byproduct of human activities, but molecular manufacturing will provide opportunities to affect it deliberately in positive ways. As with medicine, improving the environment will have to be done with careful respect for the complexity of its systems. However, also as with medicine, increased ability to monitor large areas or volumes of the environment in detail will allow the effects of interventions to be known far more quickly and reliably. This alone will help to reduce accidental damage. Existing damage that requires urgent remediation will in many cases be able to be corrected with far fewer side effects.

Perhaps the main benefit of molecular manufacturing for environmental cleanup is the sheer scale of manufacturing that will be possible when the supply of nanofactories is effectively unlimited. To deal with invasive species, for example, it may be sufficient to design a robot that physically collects and/or destroys the organisms. Once designed and tested, as many copies as required could be built, then deployed across the entire invaded range, allowed to work in parallel for a few days or weeks, and then collected. Such systems could be sized to their task, and contain monitoring apparatus to minimize unplanned impacts. Because robots would be lighter than humans and have better sensors, they could be designed to do significantly less damage and require far fewer resources than direct human intervention. However, robotic navigation software is not yet fully developed, and it will not be trivial even with million-times better computers. Furthermore, the mobility and power supply of small robots will be limited. Cleanup of chemical contamination in soil or groundwater also may be less amenable to this approach without significant disruption.

Advanced military technology may have an immense impact on our future. It seems clear that even a modest effort at developing nano-built weapon systems will create systems that will be able to totally overwhelm today's systems and soldiers. Even something as simple as multi-scale semi-automated aircraft could be utterly lethal to exposed soldiers and devastating to most equipment. With the ability to build as many weapons as desired, and with motors, sensors, and materials that far outclass biological equivalents, there would be no need to put soldiers on the battlefield at all. Any military operation that required humans to accompany its machines would quickly be overcome. Conventional aircraft could also be out-flown and destroyed with ease. In addition to offensive weapons, sensing and communications networks with millions if not billions of distributed components could be built and deployed. Software design for such things would be far from trivial, however.

It is less clear that a modest military development effort would be able to create an effective defense against today's high-tech attack systems. Nuclear explosives would have to be stopped before the explosion, and intercepting or destroying missiles in flight is not easy even with large quantities of excellent equipment. Hypersonic aircraft and battle lasers are only now being developed, and may be difficult to counter or to develop independently without expert physics knowledge and experience. However, even a near parity of technology level would give the side with molecular manufacturing a decisive edge in a non-nuclear exchange, because they could quickly build so many more weapons.

It is also uncertain what would happen in an arms race between opponents that both possessed molecular manufacturing. Weapons would be developed very rapidly up to a certain point. Beyond that, new classes of weapons would have to be invented. It is not yet known whether offensive weapons will in general be able to penetrate shields, especially if the weapons of both sides are unfamiliar to their opponents. If shields win, then development of defensive technologies may proceed rapidly until all sides feel secure. If offense wins, then a balance of terror may result. However, because sufficient information may allow any particular weapon system to be shielded against, there may be an incentive to continually develop new weapons.

This overview has focused on the earliest applications of molecular manufacturing. Later developments will benefit from previous experience, as well as from new software tools such as genetic algorithms and partially automated design. But even a cursory look at the things we can plan for today and the problems that will be most limiting early in the technology's history shows that molecular manufacturing will rapidly revolutionize many important areas of human endeavor.