Productive Nanosystems as a Milestone Toward Geoethical Nanotechnology
James B. Lewis, Ph.D.
Page 7 of 7
Advances in DNA devices
A team led by Zhaoxiang Deng has improved DNA tweezers to provide better control in capturing, holding, and releasing target molecules [40]. The improvements depend on the ability to form triple-strand DNA molecules under certain conditions.
A team led by Andrew Turberfield has improved bipedal DNA walkers—DNA nanostructures that walk along a DNA track powered by hybridization of added DNA fuel strands—so that the walkers remain on the DNA track and only move forward [41]. The device is designed so that as one DNA foot steps down, the other must lift off. Further, the DNA feet themselves catalyze the release of energy to power the walk when the feet lift free of the DNA track.
Two-armed DNA robot
A team led by Nadrian C. Seeman made a particularly significant advance by combining two independently controlled nanomechanical devices and a DNA origami framework to position the two devices with respect to each other so that they cooperate to capture specific DNA building blocks [42]. The ability to position DNA devices in a DNA framework with atomic precision means an addressable DNA surface could be dynamically programmed for various purposes.
Reducing cost of structural DNA nanotechnology
One of the key impediments to large scale use of structural DNA nanotechnology is that synthetic DNA is expensive, as discussed by Eric Drexler [43]. Drexler posts a roadmap prepared by George Church for radically reducing the cost of synthetic DNA precursors, in part by engineering bacteria to make more of the four nucleoside triphosphates and by increasing secretion of DNA by bacteria to prevent DNA from accumulating within bacteria to toxic levels.
Even more limiting than the cost of the precursors for synthetic DNA has been the expense of preparing DNA nanostructures step by step in the laboratory. Researchers led by Nadrian Seeman and Hao Yan have succeeded in cloning two complex DNA nanostructures in bacteria, surprising some observers by demonstrating that the complicated structures do not interfere with DNA replication in the bacterial cells [44]. This achievement not only opens the door to quick, less expensive ways of making DNA nanostructures so that structural DNA nanotechnology can now be scaled up, but it also implies that it might be possible to apply Darwinian selection to improve molecular devices.
Synthetic ribosomes created and they synthesize protein
George Church has announced an exciting result by an unconventional route, so that at this point the important details are not available. The creation of synthetic ribosomes that function to make protein may open the way to engineering ribosome-like structures to make polymers that can not be made by natural ribosomes [45].
Summing up
For the tip-based path toward advanced nanotechnology, the diamond mechanosynthesis area now has a very firm theoretical foundation, and the ability to write complex atomically precise patterns on a surface, at room temperature, using only mechanical force, is an experimentally established fact. Major experimental efforts have been initiated to test the theoretical proposals for diamond mechanosynthesis and to develop the patterned atomic layer epitaxy route based upon atomically precise surface depassivation.
The greater volume of experimental progress has accrued in the bio-based path of modular molecular composite nanosystems through accelerating incremental progress in a variety of technologies. Major milestones in engineering proteins have been achieved. A steady stream of results have advanced structural DNA nanotechnology along a number of fronts, including more robust nanostructures, better devices, and more complex functional constructions.
What’s missing?
It would be exceedingly useful to establish a process for timely review of theoretical and experimental progress in all of the relevant technologies so that new results can be evaluated for impact on the roadmap.
Although the roadmap is very clear about long-term goals, present capabilities, and near-term goals for diverse enabling technologies, it lacks a mid-term plan for both tip-based and bio-based pathways. How will small, atomically precise, three-dimensional parts crafted by macroscopic scanning probe instruments be combined to produce APPNs? How will composites of molecular modules be modified to produce APPNs?
Providing these missing pieces, extending and updating the roadmap and developing the pathway technologies all deserve our serious attention. Technological immortality, abundance, and the thriving of consciousness throughout the universe await us.
Appendix: Roadmap Terminology
The following definitions are direct quotations from pp 1-2 of Productive Nanosystems: A Technology Roadmap (198 pages, 2.1 MB PDF)
http://www.foresight.org/...
Nanosystems are interacting nanoscale structures, components, and devices.
Functional nanosystems are nanosystems that process material, energy, or information.
Atomically precise structures are structures that consist of a specific arrangement of atoms.
Atomically precise technology (APT) is any technology that exploits atomically precise structures of substantial complexity.
Atomically precise functional nanosystems (APFNs) are functional nanosystems that incorporate one or more nanoscale components that have atomically precise structures of substantial complexity.
Atomically precise self-assembly (APSA) is any process in which atomically precise structures align spontaneously and bind to form an atomically precise structure of substantial complexity.
Atomically precise manufacturing (APM) is any manufacturing technology that provides the capability to make atomically precise structures, components, and devices under programmable control.
Atomically precise productive nanosystems (APPNs) are functional nanosystems that make atomically precise structures, components, and devices under programmable control, that is, they are advanced functional nanosystems that perform atomically precise manufacturing.
Footnotes
[40] The results are discussed in a Nanowerk Spotlight article written by Michael Berger "The gripping potential of DNA nanotechnology". The research was published in the Journal of the American Chemical Society. “Catch and Release: DNA Tweezers that Can Capture, Hold, and Release an Object under Control” Xiaogang Han, Zihao Zhou, Fan Yang and Zhaoxiang Deng. Journal of the American Chemical Society 130: 14414–14415 (2008). Abstract.
[41] Descriptions of the improved walker are given by Jessica Griggs at NewScientist.com (Nanobot lets DNA legs do the walking), by Richard Jones on his Soft Machines blog (A synthetic, DNA based molecular motor), and in a Physical Review Focus piece by Sarah Webb (Putting One Foot in Front of the Other). The research was published in Physical Review Letters. “Coordinated Chemomechanical Cycles: A Mechanism for Autonomous Molecular Motion” S. J. Green, J. Bath, and A. J. Turberfield. Physical Review Letters 101: 238101 [4 pages] (2008). Abstract.
[42] The research was published in Nature Nanotechnology. "Dynamic patterning programmed by DNA tiles captured on a DNA origami substrate" Hongzhou Gu, Jie Chao, Shou-Jun Xiao & Nadrian C. Seeman. Published online: 15 February 2009. Abstract. The results are described in a news release from New York University, via AAAS EurekAlert “Chemists create two-armed nanorobotic device to maneuver world's tiniest particles” and by Jim Lewis on Nanodot “Structural DNA nanotechnology arrays devices to capture molecular building blocks”.
[43] Low-Cost DNA Production Roadmap posted by Eric Drexler on Dec. 21, 2008.
[44] The research was published in the Proceedings of the National Academy of Sciences. "In vivo cloning of artificial DNA nanostructures" Chenxiang Lin, Sherri Rinker, Xing Wang, Yan Liu, Nadrian C. Seeman, and Hao Yan. Proceedings of the National Academy of Science 105: 17626-17631 (2008). Abstract. The results are described in a news release from Arizona State University, via AAAS EurekAlert “Using living cells as nanotechnology factories” and discussed in more detail by Philip Ball at Nature News “Nanotech comes alive: Viruses and bacteria act as factories for nanostructures“.
[45] The accomplishment was announced in an article written by Alvin Powell, Harvard News Office, “Taking a stride toward synthetic life“. See also “Synthetic ribosomes may prove useful tool for nanotechnology” by Jim Lewis on Nanodot.
Bio
Dr. James B. Lewis holds a Ph.D. in the field of biochemistry from Harvard University. His interests include the convergence of biotechnology, artificial intelligence, information science, and cognitive science. Fascinated by current and advanced nanotechnologies, Dr. Lewis applies his knowledge to the writing and editing of works associated with nanotechnologies in hopes of solving the world’s most pressing human problems.