Nanotechnology is the term given to those areas of science and engineering where phenomena that take place at dimensions in the nanometre scale are utilised in the design, characterisation, production and application of materials, structures, devices and systems. Although in the natural world there are many examples of structures that exist with nanometre dimensions (hereafter referred to as the nanoscale), including essential molecules within the human body and components of foods, and although many technologies have incidentally involved nanoscale structures for many years, it has only been in the last quarter of a century that it has been possible to actively and intentionally modify molecules and structures within this size range. It is this control at the nanometre scale that distinguishes nanotechnology from other areas of technology.
Clearly the various forms of nanotechnology have the potential to make a very significant impact on society. In general it may be assumed that the application of nanotechnology will be very beneficial to individuals and organisations. Many of these applications involve new materials which provide radically different properties through functioning at the nanoscale, where new phenomena are associated with the very large surface area to volume ratios experienced at these dimensions and with quantum effects that are not seen with larger sizes. These include materials in the form of very thin films used in catalysis and electronics, two-dimensional nanotubes and nanowires for optical and magnetic systems, and as nanoparticles used in cosmetics, pharmaceuticals and coatings. The industrial sectors most readily embracing nanotechnology are the information and communications sector, including electronic and optoelectronic fields, food technology, energy technology and the medical products sector, including many different facets of pharmaceuticals and drug delivery systems, diagnostics and medical technology, where the terms nanomedicine and bionanotechnology are already commonplace. Nanotechnology products may also offer novel challengies for the reduction of environmental pollution.
However, just as phenomena taking place at the nanoscale may be quite different to those occurring at larger dimensions and may be exploitable for the benefit of mankind, so these newly identified processes and their products may expose the same humans, and the environment in general, to new health risks, possibly involving quite different mechanisms of interference with the physiology of human and environmental species. These possibilities may well be focussed on the fate of free nanoparticles generated in nanotechnology processes and either intentionally or unintentionally released into the environment, or actually delivered directly to individuals through the functioning of a nanotechnology based product. Of special concern would be those individuals whose work places them in regular and sustained contact with free nanoparticles. Central to these health risk concerns is the fact that evolution has determined that the human species has developed mechanisms of protection against environmental agents, either living or dead, this process being determined by the nature of the agents commonly encountered, within which size is an important factor. The exposure to nanoparticles having characteristics not previously encountered may well challenge the normal defence mechanisms associated with, for example, immune and inflammatory systems. It is also possible for there to be an environmental impact of the products of nanotechnology, related to the processes of dispersion and persistence of nanoparticles in the environment.
Wherever the potential for an entirely new risk is identified, it is necessary to carry out an extensive analysis of the nature of the risk, which can then, if necessary, be used in the processes of risk management. It is widely accepted that the risks associated with nanotechnology need to be analysed in this way. Many international organisations ( e.g. Asia Pacific Nanotechnology Forum 2005), governmental bodies within the European Union (European Commission 2004,), National Institutions (e.g. De Jong et al 2005, Roszek et al 2005, US National Science and Technology Council 2004, IEEE 2004, US National Institute of Environmental Health Sciences 2004), non-governmental organisations (e.g.UN-NGLS 2005), learned institutions and societies (e.g. Institute of Nanotechnology 2005, Australian Academy of Sciences 2005, METI 2005, UK Royal Society and Royal Academy of Engineering 2004) and individuals (e.g. Oberdörster et al 2005, Donaldson and Stone 2003) have published reports on the current state of nanotechnology, and most draw attention to this need for a thorough risk analysis.
The European Council has highlighted the need to pay special attention to the potential risks throughout the life cycle of nanotechnology based products and the European Commission has signalled its intention to work on an international basis towards establishing a framework of shared principles for the safe, sustainable, responsible and socially acceptable use of nanotechnologies.
3.2 Definitions and Scope
There are several definitions of nanotechnology and of the products of nanotechnology, often these been generated for specific purposes.
In this Opinion, the underlying scientific concepts of nanotechnology have been considered more important than the semantics of a definition, so these are considered first. The Committee considers that the scope of nanoscience and nanotechnology used by the UK Royal Society and Royal Academy of Engineering in their 2004 report (Royal Society and Royal Academy of Engineering 2004) adequately expresses these concepts. This suggests that the range of the nanoscale is from the atomic level, at around 0.2 nm up to around 100nm. It is within this range that materials can have substantially different properties compared to the same substances at larger sizes, both because of the substantially increased ratio of surface area to mass, and also because quantum effects begin to play a role at these dimensions, leading to significant changes in several types of physical property.
The present Opinion uses the various terms of nanotechnology in a manner consistent with the recently published Publicly Available Specification on the Vocabulary for Nanoparticles of the British Standards Institution (BSI 2005), in which the following definitions for the major general terms are proposed:
Nanoscale: having one or more dimensions of the order of 100 nm or less.
Nanoscience: the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale.
Nanotechnology: the design, characterization, production and application of structures, devices and systems by controlling shape and size at the nanoscale.
Nanomaterial: material with one or more external dimensions, or an internal structure, which could exhibit novel characteristics compared to the same material without nanoscale features.
Nanoparticle: particle with one or more dimensions at the nanoscale. (Note: In the present report, nanoparticles are considered to have two or more dimensions at the nanoscale).
Nanocomposite: composite in which at least one of the phases has at least one dimension on the nanoscale.
Nanostructured: having a structure at the nanoscale,
It should be noted that nanoscience and nanotechnology have been emerging rapidly during recent years, and that the vocabulary used within the contributing disciplines has not been consistent during this time. Also, as this report notes, there have been, and continue to be, serious difficulties with the precise measurement of the parameters of the nanoscale, such that it is not always possible to have complete confidence in the data and conclusions drawn about specific phenomena relating to specific features of nanostructures and nanomaterials. This Opinion recognises the inevitability of this situation and has drawn some general conclusions in the knowledge that the literature may contain inconsistencies and inaccuracies. Whilst, therefore, this Opinion uses the definition that nanoscale should now be considered to involve dimensions up to 100 nm, it recognises that some of the literature will have represented nanoscale as having larger dimensions than 100 nm. Much of the literature related to particles, especially that concerned with aerosols, air pollution and inhalation toxicology, has referred to particles as either ultrafine, fine or conventional. This report has assumed that, unless otherwise stated, ‘ultrafine particles’ are essentially equivalent to nanoparticles.
Also, in relation to nanoparticles, it must be borne in mind that a sample of a substance that contains nanoparticles will not be monodisperse, but will normally contain a range of particle sizes. This makes it even more difficult to assess accurately the parameters of the nanoscale, especially when considering the doses for toxicological studies. In this Opinion reference is frequently made to studies of exposure and toxicology data concerned with particles and will quote the particle size given in the papers as either single figures (e.g. 40 nm) or ranges (e.g. 40 – 80 nm) recognising that these will be approximations.
Moreover, there will be a tendency in some situations for nanoparticles to aggregate. It might be assumed that an aggregate of nanoparticles, which may have dimensions measured in microns rather than nanometres, would behave differently to the individual nanoparticles, but at the same time there is no reason to expect the aggregate to behave like one large particle. Equally, it might be expected that the behaviour of nanoparticles will be dependent on their solubility and susceptibility to degradation and that neither the chemical composition nor particle size are guaranteed to remain constant over time.
With the above definitions and caveats in mind, it is clear that, as far as both intrinsic properties and health risks are concerned, there are two types of nanostructure to consider, those where the structure itself is a free particle and those where the nanostructure is an integral feature of a larger object.
It is the former group, involving free nanoparticles, that provides the greater concern with respect to health risks, and which is the subject of the major part of this Opinion. The term ‘free’ should be qualified, since it implies that at some stage in production or use the substance in question consists of individual particles, of nanoscale dimensions. In the application of the substance, these individual particles may be incorporated into a quantity of another substance, which could be a gas, a liquid or a solid, typically to produce a paste, a gel or a coating. These particles may still be considered to be free, although their bioavailability will vary with the nature of the phase in which they are dispersed. Ultrafine aerosols and colloids, and cream-based cosmetics and pharmaceutical preparations would be included in this category, and it is with these examples that much of the recent work on nanotechnology health risks has been concerned.
This opinion essentially discusses the potential risks associated with the manufacture and use of products incorporating engineered nanomaterials. Nanostructures of biological origin such as proteins, phospholipids, lipids etc. are not considered in this context.
What Is Nanotechnology?
Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is about 1 to 100 nanometers.
Physicist Richard Feynman, the father of nanotechnology.
Nanoscience and nanotechnology are the study and application of extremely small things and can be used across all the other science fields, such as chemistry, biology, physics, materials science, and engineering.
How It Started
The ideas and concepts behind nanoscience and nanotechnology started with a talk entitled “There’s Plenty of Room at the Bottom” by physicist Richard Feynman at an American Physical Society meeting at the California Institute of Technology (CalTech) on December 29, 1959, long before the term nanotechnology was used. In his talk, Feynman described a process in which scientists would be able to manipulate and control individual atoms and molecules. Over a decade later, in his explorations of ultraprecision machining, Professor Norio Taniguchi coined the term nanotechnology. It wasn’t until 1981, with the development of the scanning tunneling microscope that could «see» individual atoms, that modern nanotechnology began.
Fundamental Concepts in Nanoscience and Nanotechnology
Medieval stained glass windows are an example of how nanotechnology was used in the pre-modern era. (Courtesy: NanoBioNet)
Nanoscience and nanotechnology involve the ability to see and to control individual atoms and molecules. Everything on Earth is made up of atoms—the food we eat, the clothes we wear, the buildings and houses we live in, and our own bodies.
But something as small as an atom is impossible to see with the naked eye. In fact, it’s impossible to see with the microscopes typically used in a high school science classes. The microscopes needed to see things at the nanoscale were invented in the early 1980s.
Once scientists had the right tools, such as the scanning tunneling microscope (STM) and the atomic force microscope (AFM), the age of nanotechnology was born.
Although modern nanoscience and nanotechnology are quite new, nanoscale materials were used for centuries. Alternate-sized gold and silver particles created colors in the stained glass windows of medieval churches hundreds of years ago. The artists back then just didn’t know that the process they used to create these beautiful works of art actually led to changes in the composition of the materials they were working with.
Today’s scientists and engineers are finding a wide variety of ways to deliberately make materials at the nanoscale to take advantage of their enhanced properties such as higher strength, lighter weight, increased control of light spectrum, and greater chemical reactivity than their larger-scale counterparts.
An Introduction to Nanotechnology
Nanotechnology is defined as the study and use of structures between 1 nanometer and 100 nanometers in size. To give you an idea of how small that is, it would take eight hundred 100 nanometer particles side by side to match the width of a human hair.
While this is the most common definition of nanotechnology researchers with various focuses have slightly different definitions. For a summary of these different definitions see Definitions of Nanotechnology,
Introduction to Nanotechnology: Looking At Nanoparticles
Scientists have been studying and working with nanoparticles for centuries, but the effectiveness of their work has been hampered by their inability to see the structure of nanoparticles. In recent decades the development of microscopes capable of displaying particles as small as atoms has allowed scientists to see what they are working with.
The following illustration titled “The Scale of Things”, created by the U. S. Department of Energy, provides a comparison of various objects to help you begin to envision exactly how small a nanometer is. The chart starts with objects that can be seen by the unaided eye, such as an ant, at the top of the chart, and progresses to objects about a nanometer or less in size, such as the ATP molecule used in humans to store energy from food.
Now that you have an idea of how small a scale nanotechnologists work with, consider the challenge they face. Think about how difficult it is for many of us to insert thread through the eye of a needle. Such an image helps you imagine the problem scientists have working with nanoparticles that can be as much as one millionth the size of the thread. Only through the use of powerful microscopes can they hope to ‘see’ and manipulate these nano-sized particles. Browsing through our Nanoparticle Applications page will help you understand how nanoparticles are being used.
Introduction to Nanotechnology Applications
The ability to see nano-sized materials has opened up a world of possibilities in a variety of industries and scientific endeavors. Because nanotechnology is essentially a set of techniques that allow manipulation of properties at a very small scale, it can have many applications, such as the ones listed below.
Drug delivery. Today, most harmful side effects of treatments such as chemotherapy are a result of drug delivery methods that don’t pinpoint their intended target cells accurately. Researchers at Harvard and MIT have been able to attach special RNA strands, measuring about 10 nm in diameter, to nanoparticles and fill the nanoparticles with a chemotherapy drug. These RNA strands are attracted to cancer cells. When the nanoparticle encounters a cancer cell it adheres to it and releases the drug into the cancer cell. This directed method of drug delivery has great potential for treating cancer patients while producing less side harmful affects than those produced by conventional chemotherapy.
Fabrics. The properties of familiar materials are being changed by manufacturers who are adding nano-sized components to conventional materials to improve performance. For example piezoelectric fibers are being devloped that could allow clothing to generate electricity through normal motions.
Reactivity of Materials. The properties of many conventional materials change when formed as nano-sized particles (nanoparticles). This is generally because nanoparticles have a greater surface area per weight than larger particles; they are therefore more reactive to some other molecules. For example studies have show that nanoparticles of iron can be effective in the cleanup of chemicals in groundwater because they react more efficiently to those chemicals than larger iron particles.
Strength of Materials. Nano-sized particles of carbon, (for example nanotubes and bucky balls) are extremely strong. Nanotubes and bucky balls are composed of only carbon and their strength comes from special characteristics of the bonds between carbon atoms. One proposed application that illustrates the strength of nanosized particles of carbon is the manufacture of t-shirt weight bullet proof vests made out of carbon nanotubes.
Micro/Nano ElectroMechanical Systems. The ability to create gears, mirrors, sensor elements, as well as electronic circuitry in silicon surfaces allows the manufacture of miniature sensors such as those used to activate the airbags in your car. This technique is called MEMS (Micro-ElectroMechanical Systems). The MEMS technique results in close integration of the mechanical mechanism with the necessary electronic circuit on a single silicon chip, similar to the method used to produce computer chips. Using MEMS to produce a device reduces both the cost and size of the product, compared to similar devices made with conventional methods. MEMS is a stepping stone to NEMS or Nano-ElectroMechanical Systems. NEMS products are being made by a few companies, and will take over as the standard once manufacturers make the investment in the equipment needed to produce nano-sized features.
Molecular Manufacturing. If you’re a Star Trek fan, you remember the replicator, a device that could produce anything from a space age guitar to a cup of Earl Grey tea. Your favorite character just programmed the replicator, and whatever he or she wanted appeared. Researchers are working on developing a method called molecular manufacturing that may someday make the Star Trek replicator a reality. The gadget these folks envision is called a molecular fabricator; this device would use tiny manipulators to position atoms and molecules to build an object as complex as a desktop computer. Researchers believe that raw materials can be used to reproduce almost any inanimate object using this method.
The Nanotechnology Debate
There are many different points of view about the nanotechnology. These differences start with the definition of nanotechnology. Some define it as any activity that involves manipulating materials between one nanometer and 100 nanometers. However the original definition of nanotechnology involved building machines at the molecular scale and involves the manipulation of materials on an atomic (about two-tenths of a nanometer) scale.
The debate continues with varying opinions about exactly what nanotechnology can achieve. Some researchers believe nanotechnology can be used to significantly extend the human lifespan or produce replicator-like devices that can create almost anything from simple raw materials. Others see nanotechnology only as a tool to help us do what we do now, but faster or better.
The third major area of debate concerns the timeframe of nanotechnology-related advances. Will nanotechnology have a significant impact on our day-to-day lives in a decade or two, or will many of these promised advances take considerably longer to become realities?
Finally, all the opinions about what nanotechnology can help us achieve echo with ethical challenges. If nanotechnology helps us to increase our lifespans or produce manufactured goods from inexpensive raw materials, what is the moral imperative about making such technology available to all? Is there sufficient understanding or regulation of nanotech based materials to minimize possible harm to us or our environment?
Only time will tell how nanotechnology will affect our lives, but browsing through the topics on the navigation bar above or on our Nanotechnology Applications page will help you understand the possibilities and anticipate the future.
What is nanotechnology?
During the Middle Ages, philosophers attempted to transmute base materials into gold in a process called alchemy. While their efforts proved fruitless, the pseudoscience alchemy paved the way to the real science of chemistry. Through chemistry, we learned more about the world around us, including the fact that all matter is composed of atoms. The types of atoms and the way those atoms join together determines a substance’s properties.
We could make other interesting substances, though. By manipulating molecules to form in particular shapes, we can build materials with amazing properties. One example is a carbon nanotube. To create a carbon nanotube, you start with a sheet of graphite molecules, which you roll up into a tube. The orientation of the molecules determines the nanotube’s properties. For example, you could end up with a conductor or a semiconductor. Rolled the right way, the carbon nanotube will be hundreds of times stronger than steel but only one-sixth the weight [source: NASA].
That’s just one aspect of nanotechnology. Another is that materials aren’t the same at the nanoscale as they are at larger scales. Researchers with the United States Department of Energy discovered in 2005 that gold shines differently at the nanoscale than it does in bulk. They also noticed that materials possess different properties of magnetism and temperature at the nanoscale [source: U.S. Department of Energy].
Learn more about nanotechnology by following the links on the next page.
Nanotechnology
Nanotechnology (sometimes shortened to «nanotech«) is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with developing materials, devices, or other structures possessing at least one dimension sized from 1 to 100 nanometres. Quantum mechanical effects are important at this quantum-realm scale.
Nanotechnology is very diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale to investigating whether we can directly control matter on the atomic scale. Nanotechnology entails the application of fields of science as diverse as surface science, organic chemistry, molecular biology, semiconductor physics, microfabrication, etc.
There is much debate on the future implications of nanotechnology. Nanotechnology may be able to create many new materials and devices with a vast range of applications, such as in medicine, electronics, biomaterials and energy production. On the other hand, nanotechnology raises many of the same issues as any new technology, including concerns about the toxicity and environmental impact of nanomaterials, [ 1 ] and their potential effects on global economics, as well as speculation about various doomsday scenarios. These concerns have led to a debate among advocacy groups and governments on whether special regulation of nanotechnology is warranted.
Contents
Origins
Although nanotechnology is a relatively recent development in scientific research, the development of its central concepts happened over a longer period of time. The emergence of nanotechnology in the 1980s was caused by the convergence of experimental advances such as the invention of the scanning tunneling microscope in 1981 and the discovery of fullerenes in 1985, with the elucidation and popularization of a conceptual framework for the goals of nanotechnology beginning with the 1986 publication of the book Engines of Creation.
The scanning tunneling microscope, an instrument for imaging surfaces at the atomic level, was developed in 1981 by Gerd Binnig and Heinrich Rohrer at IBM Zurich Research Laboratory, for which they received the Nobel Prize in Physics in 1986. [ 2 ] [ 3 ] Fullerenes were discovered in 1985 by Harry Kroto, Richard Smalley, and Robert Curl, who together won the 1996 Nobel Prize in Chemistry. [ 4 ] [ 5 ]
Around the same time, K. Eric Drexler developed and popularized the concept of nanotechnology and founded the field of molecular nanotechnology. In 1979, Drexler encountered Richard Feynman’s 1959 talk «There’s Plenty of Room at the Bottom». The term «nanotechnology», originally coined by Norio Taniguchi in 1974, was unknowingly appropriated by Drexler in his 1986 book Engines of Creation: The Coming Era of Nanotechnology, which proposed the idea of a nanoscale «assembler» which would be able to build a copy of itself and of other items of arbitrary complexity. He also first published the term «grey goo» to describe what might happen if a hypothetical self-replicating molecular nanotechnology went out of control. Drexler’s vision of nanotechnology is often called «Molecular Nanotechnology» (MNT) or «molecular manufacturing,» and Drexler at one point proposed the term «zettatech» which never became popular.
In the early 2000s, the field was subject to growing public awareness and controversy, with prominent debates about both its potential implications, exemplified by the Royal Society’s report on nanotechnology, [ 6 ] as well as the feasibility of the applications envisioned by advocates of molecular nanotechnology, which culminated in the public debate between Eric Drexler and Richard Smalley in 2001 and 2003. [ 7 ] Governments moved to promote and fund research into nanotechnology with programs such as the National Nanotechnology Initiative.
The early 2000s also saw the beginnings of commercial applications of nanotechnology, although these were limited to bulk applications of nanomaterials, such as the Silver Nano platform for using silver nanoparticles as an antibacterial agent, nanoparticle-based transparent sunscreens, and carbon nanotubes for stain-resistant textiles. [ 8 ] [ 9 ]
Fundamental concepts
Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced. In its original sense, nanotechnology refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products.
To put that scale in another context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth. [ 12 ] Or another way of putting it: a nanometer is the amount an average man’s beard grows in the time it takes him to raise the razor to his face. [ 12 ]
Two main approaches are used in nanotechnology. In the «bottom-up» approach, materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In the «top-down» approach, nano-objects are constructed from larger entities without atomic-level control. [ 13 ]
Areas of physics such as nanoelectronics, nanomechanics, nanophotonics and nanoionics have evolved during the last few decades to provide a basic scientific foundation of nanotechnology.
Larger to smaller: a materials perspective
A number of physical phenomena become pronounced as the size of the system decreases. These include statistical mechanical effects, as well as quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, quantum effects become dominant when the nanometer size range is reached, typically at distances of 100 nanometers or less, the so called quantum realm. Additionally, a number of physical (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal and catalytic properties of materials. Diffusion and reactions at nanoscale, nanostructures materials and nanodevices with fast ion transport are generally referred to nanoionics. Mechanical properties of nanosystems are of interest in the nanomechanics research. The catalytic activity of nanomaterials also opens potential risks in their interaction with biomaterials.
Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); stable materials turn combustible (aluminum); insoluble materials become soluble (gold). A material such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these quantum and surface phenomena that matter exhibits at the nanoscale. [ 14 ]
Simple to complex: a molecular perspective
Modern synthetic chemistry has reached the point where it is possible to prepare small molecules to almost any structure. These methods are used today to manufacture a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. This ability raises the question of extending this kind of control to the next-larger level, seeking methods to assemble these single molecules into supramolecular assemblies consisting of many molecules arranged in a well defined manner.
These approaches utilize the concepts of molecular self-assembly and/or supramolecular chemistry to automatically arrange themselves into some useful conformation through a bottom-up approach. The concept of molecular recognition is especially important: molecules can be designed so that a specific configuration or arrangement is favored due to non-covalent intermolecular forces. The Watson–Crick basepairing rules are a direct result of this, as is the specificity of an enzyme being targeted to a single substrate, or the specific folding of the protein itself. Thus, two or more components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.
Such bottom-up approaches should be capable of producing devices in parallel and be much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. Nevertheless, there are many examples of self-assembly based on molecular recognition in biology, most notably Watson–Crick basepairing and enzyme-substrate interactions. The challenge for nanotechnology is whether these principles can be used to engineer new constructs in addition to natural ones.
Molecular nanotechnology: a long-term view
Molecular nanotechnology, sometimes called molecular manufacturing, describes engineered nanosystems (nanoscale machines) operating on the molecular scale. Molecular nanotechnology is especially associated with the molecular assembler, a machine that can produce a desired structure or device atom-by-atom using the principles of mechanosynthesis. Manufacturing in the context of productive nanosystems is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.
When the term «nanotechnology» was independently coined and popularized by Eric Drexler (who at the time was unaware of an earlier usage by Norio Taniguchi) it referred to a future manufacturing technology based on molecular machine systems. The premise was that molecular scale biological analogies of traditional machine components demonstrated molecular machines were possible: by the countless examples found in biology, it is known that sophisticated, stochastically optimised biological machines can be produced.
It is hoped that developments in nanotechnology will make possible their construction by some other means, perhaps using biomimetic principles. However, Drexler and other researchers [ 15 ] have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles, namely, a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) that would enable programmable, positional assembly to atomic specification. [ 16 ] The physics and engineering performance of exemplar designs were analyzed in Drexler’s book Nanosystems.
In general it is very difficult to assemble devices on the atomic scale, as all one has to position atoms on other atoms of comparable size and stickiness. Another view, put forth by Carlo Montemagno, [ 17 ] is that future nanosystems will be hybrids of silicon technology and biological molecular machines. Yet another view, put forward by the late Richard Smalley, is that mechanosynthesis is impossible due to the difficulties in mechanically manipulating individual molecules.
This led to an exchange of letters in the ACS publication Chemical & Engineering News in 2003. [ 18 ] Though biology clearly demonstrates that molecular machine systems are possible, non-biological molecular machines are today only in their infancy. Leaders in research on non-biological molecular machines are Dr. Alex Zettl and his colleagues at Lawrence Berkeley Laboratories and UC Berkeley. They have constructed at least three distinct molecular devices whose motion is controlled from the desktop with changing voltage: a nanotube nanomotor, a molecular actuator, [ 19 ] and a nanoelectromechanical relaxation oscillator. [ 20 ] See nanotube nanomotor for more examples.
An experiment indicating that positional molecular assembly is possible was performed by Ho and Lee at Cornell University in 1999. They used a scanning tunneling microscope to move an individual carbon monoxide molecule (CO) to an individual iron atom (Fe) sitting on a flat silver crystal, and chemically bound the CO to the Fe by applying a voltage.
