This brief document is written in response to the general confusion there is with respect to nanotechnology and its aspects. It is intended as a response to assertions that have been made by journals like Scientific American [1] and organizations like the Nanobusiness Alliance [2] that robust nanotechnology is impossible.
There are two key aspects of nanotechnology: scale and strength.
Regarding scale, the National Science Foundation has defined nanotechnology as between 1 and 100 nanometers (nm) in size. On the low end this is larger than common molecules such as water or carbon dioxide. On the high end it is smaller than most bacteria and much smaller than mammalian cells.
Regarding strength, one way of looking at this is the number of covalent bonds per unit volume. In this respect diamond and buckytubes are fairly high while most biological molecules, including those like actin which makes up the cytoskeleton of cells rank much lower. However in some cases there are biological molecules such as spider silk that can push the numbers to higher levels.
So almost all of the more complex molecules found in biology fit the size scale definition of nanotechnology. There are tens of thousands of these whose genomic sequence is known. Currently more than 20,000 of these molecules have had their structure analyzed and have been deposited in the Protein Database. Most of these -- proteins that function as enzymes, molecules that pump ions into or out of cells, or molecular motors that do everything from produce energy (ATP) to those that make a heart beat can be considered to be molecular machines by any reasonable definition because they perform work of one kind or another.
So it is quite reasonable to assert that biotechnology is nanotechnology.
Now where biotechnology cannot match classical molecular nanotechnology (MNT) (yet) is with respect to the number of covalent bonds per unit volume. This is due to the fact that almost all of biology revolves around proteins that are largely held together by hydrogen bonds which are weaker than covalent bonds.
A 3rd aspect of molecular nanotechnology is the whether or not the material or structures can perform work at the nanoscale level. Work is a well defined concept in physics. There are substances that may be structured at the nanoscale level which may have the strength of nanomaterials but may not actually perform any work (e.g. buckytubes). These would be nanoscale materials but would not rise to the level of nanomachinery. In contrast many of the proteins in cells can be treated as nanomachines.
There is a 4th test for nanotechnology and that involves atomic precision. In this respect biomolecules and molecular nanotechnology are quite similar. One can perform work at the nanoscale without this precision (biological molecular machines are not always precise at this level but do manage to get the job done). It is much more efficient if atomic precision is available.
At this time the semiconductor chip industry is moving chip patterns into the sub-100 nm realm (so it starts to satisfy the size scale requirement) and to a significant extent the strength requirement (silicon crystals have a covalent bond density similar to diamond) but it does not completely satisfy the atomic precision requirement to the degree that is found in biomolecules or MNT.
The final two characteristics of nanotechnology which may be important are self-assembly and self-replication. Self-assembly is not a feature that classical MNT requires. MNT as has been defined by Drexler, Merkle & Freitas prefers instead directed or positional-assembly.
Self-replication, is the primary feature that leads to the Grey Goo scenario. Though it is helpful for the rapid development of classical MNT it also is not required.
Both self-assembly and self-replication are essential aspects of most life on the Earth. The exception being viruses and some other types of biological parasites which in general can self-assemble but cannot self-replicate. It is also true that human science either has or is gaining control over these realms. Humans have used the self-replication properties of microorganisms for decades to produce drugs (from penicillin to insulin) and for thousands of years to produce alcoholic beverages.
In summary, features of molecular nanotechnology include:
When dealing with nanotech claimants one can apply these criteria one by one to see if one is discussing "real" nanotechnology or simply nanohype. Real MNT should be able to assert that it has (1), (3) and (4).
Nobody ever said combining all of these aspects of nanotechnology was going to be simple or easy. But anyone who suggests that it is impossible should be challenged to demonstrate why.