da Vinci’s Notebook, vol. 7 (2015)
Molecular Assemblers: Building From the Molecule Up Ben Kelso First Year Student (B.Sc. Nanoscience) College of Physical and Engineering Science, University of Guelph, CANADA
“But I am not afraid to consider the final have already been developed. Also some question as to whether, ultimately - in the examples from nature will be outlined as great future - we can arrange the atoms proofs-of-concept of the molecular the way we want; the very atoms, all the assembler. Finally, the paper will go over way down!” the problem of run-away self-replication of -Richard Feynman molecular assemblers. That quote, came from his 1959 Molecular assemblers are nanoscale speech "There's Plenty of Room at the machines that manipulate the molecules in Bottom", generally considered to be the their environment to build more complex conceptual origin of nanotechnology. While structures. Hypothetically, anything that can largely still theoretical, significant strides be manipulated on the molecular level could have been made towards building what be used as a building material1. Naturally, would later become known as molecular this leaves the answer quite open-ended due assemblers. So far miniaturization has to the vast possibilities for molecular taken a top-down approach, trying to find manipulation. Molecular assemblers could ways to make things we already know at build quantum computers, macroscale smaller and smaller scales, but this has a objects, other nanorobots, other fundamental limitation that will soon be nanostructures, or even copies of itself1. 1 reached at around 50 nm . Current iterations of molecular assemblers Nanotechnology, on the other hand are very narrow in their function, being able takes a bottom-up approach, attempting to to catalyze very specific reactions involving rebuild macro scale devices from the ground specific molecules. But ideally as time up, from atoms or molecules1. The world of progresses a more general "universal possible properties and applications for assembler" could be developed that can devices and structures built with molecular manipulate a wide array of molecules and precision is endless. This is the design goal consequently be able to build almost 1 of molecular assemblers: to build things anything . Note that the term molecular molecule by molecule. Since they are largely assembler is intentionally used as opposed to theoretical still, this paper will explore a atomic assemblers. It's been shown that number of the different potential controlling atoms individually is incredibly 2 applications that have been envisioned, as difficult . Molecules are much more stable well as some examples of nanomachines that than atoms and are already device-like, as
da Vinci’s Notebook (ISSN 1923-5720) is sponsored by the College of Physical and Engineering Science, University of Guelph, Canada. da Vinci’s Notebook, vol. 7 (2015) they have properties that can be manipulated particle's movement within the nanotube4. with electricity or light2. It is hard to harvest These are examples of nanoscale machines atoms from the environment, as they that already exist and could certainly be commonly exist in a bound state and would useful if incorporated into molecular require energy to unbind2. As a result of assembler design. these limitations, the field is focused on While our ability to manipulate atoms designing molecular assemblers as opposed with the level of precision to make almost to atomic assemblers. anything may seem farfetched, there are a Like any machine, the molecular number of examples from nature we can assembler would be composed of individual look to for inspiration. Ribosomes are components in which each performs a essentially biological molecular assemblers. specific action, which together with the They are composed of a number of different other components result in the assembler proteins and RNA’s. They come together to performing a function2. At the very least, it read an mRNA and take amino acids from would require an energy source, a the cytosol to form a protein. This is an component to bind and unbind molecules, a exact mirror to what molecular assemblers component that moves the molecule to the do, but replace amino acids with molecules, desired location, a computer that can dictate mRNA with computer, cytosol with the the function or a receiver if using a environment. Proteins may not necessarily broadcast architecture, and a motor for even have to be replaced, as it is likely that movement1. A number of different energy molecular assemblers will include them in sources for nanoscale machinery have their design. If nature can build a biological already been hypothesized and developed. molecular assembler, it is highly probable Taking a lead from nature, examples include that an artificial assembler can be ATP, and sunlight1. Ben Feringa from the constructed. University of Groningen in the Netherlands One of the amazing potential was able to make a solar powered advantages of advanced molecular nanomotor, out of only 58 atoms3. assemblers, is that the expense to produce Photochemical and electrochemical based something is reduced to only its materials sources are good energy reservoirs, as they costs, and the software to run the do not produce waste products which can assembler1. Truly the ultimate in affect the function of the assembler. They miniaturized 3D-printers, you could print also create processes that are reversible, anything you need when these are fully which are both desirable properties for developed, from clothing to medicine1. nanomachinery2. Scientists from the Until then, researchers will be working Lawrence Berkeley National Laboratory within the current limitations of the field. were able to make a conveyor belt out of There are examples of functional carbon nanotubes4. By controlling the molecular assemblers, but they are electrical current in the nanotube they were nowhere near the generalized universal able to direct the velocity of an indium
da Vinci’s Notebook (ISSN 1923-5720) is sponsored by the College of Physical and Engineering Science, University of Guelph, Canada. da Vinci’s Notebook, vol. 7 (2015) assemblers envisioned of the future. They replicator1. There are a number of ways to can perform very specific actions deal with this concern though, so that the involving very specific molecules. One grey goo problem can be fairly easily such example is Cucurbit[8]uril which can avoided. Among them is using the perform [2 + 2] photocycloaddition of broadcast architecture mentioned earlier, stryrl dyes5. [2 + 2] photocycloaddition is which involves having the code for self- a photochemical reaction that involves two replication present on a single computer unsaturated molecules being combined to that broadcasts it to all of the form a product molecule5. Two atoms are nanomachines, so that at anytime the involved from each of the two molecules broadcast and thus replication can be being bound, and this gives the notation [2 stopped1. The broadcast architecture is not + 2]5. infallible however, and could be defeated if someone was determined enough1. Along with all of the amazing Designers can also structure the process to potential promised by nanotechnology and require exotic or uncommon materials so molecular assemblers, it isn't without it's that it becomes a limiting factor for perils if certain contingencies aren't replication1. Other more extravagant ideas properly accounted and prepared for. In include having a nanorobot immune order to make a nanoscale factory, it isn't efficient to make a single molecular system, designed to seek out rampantly 1 assembler and watch it build your design, replicating nanorobots and eliminate them . one molecule at a time1. It is much more Ironically, this immune system would itself 1 efficient to have the molecular assembler need to be self-replicating . self-replicate a few thousand times, and Advanced universal molecular then have all the new assemblers begin assemblers are mainly theoretical but there 1 building in tandem . Unfortunately, the so- are a number of advances in nanotechnology called "grey goo" problem arises if an that indicates they may be possible in the assembler becomes coded to replicate near future. The number of individual indefinitely. This could begin either due to nanomachine components being developed, an individual with malicious intent, or the current single function molecular unintentionally due to a replication glitch. assemblers that already exist, and the In replicating thousands of times, similar to precedent already set by nature, are all DNA mutations, a glitch could happen that strong indicators that a more general causes an assembler to become "cancerous" molecular assembler is possible. Their 1 and replicate with no signal to stop . amazing potential for an advanced version to Unfortunately, if rampant self-replication make nearly anything is an exciting prospect occurred, the biomass of the Earth would for humanity. The dangers of potential 1 likely be the prime target . This is because runaway replication certainly exist, but carbon and glucose are likely to be numerous different protection methods incorporated into the replicator's designs already exist and will be developed and would therefore be of high value to the alongside the technology.
da Vinci’s Notebook (ISSN 1923-5720) is sponsored by the College of Physical and Engineering Science, University of Guelph, Canada. da Vinci’s Notebook, vol. 7 (2015)
References 1. Kurzweil, R. The Singularity is Near: When Humans Transcend Biology; Penguin Group, New York, 2006; pp 226-258, 397-402.
2. Vincenzo, B., Credi, A. Francisco M. R., Fraser, J. Fraser, S. Artificial Molecular Machines. Angew. Chem. Int. Ed. 2000, 39(19), 3348–3391.
3. N. Kourmura et al., "Light-Driven Monodirectional Molecular Rotor," Nature 401.6749 (September 9, 1999): 152-55
4. Berkeley Lab, "A Conveyor Belt for the Nano-Age," April 28, 2004, http://www2.lbl.gov/Science-Articles/Archive/MSD-conveyor-belt-for-nanoage.html
5. Sergey, P. G., Artem,I. V., Lyudmila, G. K., Dmitry, V. K., Sergey, K. S., Yuri, A. S., Michael, V. A., Judith, A. K. H. Photocontrolled Molecular Assembler Based on Cucurbit[8]uril: [2+2]-Autophotocycloaddition of Styryl Dyes in the Solid State and in Water. Eur. J. Org. Chem. 2010, No. 13, 2587-2599.
da Vinci’s Notebook (ISSN 1923-5720) is sponsored by the College of Physical and Engineering Science, University of Guelph, Canada.