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Posted: Mar 20, 2008

Brain for nanobots?

(Nanowerk Spotlight) In our Nanowerk Spotlights we usually stay with both feet firmly on the grounds of science and shy away from the science fiction and sensationalist aspects of nanotechnology. So today's headline might come as a surprise to you (but just to be safe we put a question mark in). Of course, there are no nanobots yet, and won't be for a while, but one of the fundamental problems to be solved for possible future molecular machinery is the challenge of controlling many molecule-sized machines simultaneously to perform a desired task. Simple nanoscale motors have been realized over the past few years but these are systems that do nothing more than generate physical motion of their components at a nanoscale level. An example is a story we wrote a while back about nanoscale monorail cargo shuttles.
To build a true nanorobot - a completely self-contained electronic, electric, or mechanical device to do such activities as manufacturing at the nanoscale - many breakthrough advances will need to be achieved (background read: Mind the gap - nanotechnology robotics vision versus lab reality). One of them is the issue of controlling large numbers of devices, i.e. how to build and program the 'brains' of these machines. Another issue is to separate the concept of science fiction style 'thinking' robots (artificial intelligence) from a more realistic (yet still distant) concept of machines that can be programmed to perform a limited task in a more or less autonomous way for a period of time. These tasks could range from fabricating nanoscale components to performing medical procedures inside the body. For nanoscale machinery this would require the availability of nanoscale control units, i.e. computers. Researchers in Japan are now reporting a self organizing 16-bit parallel processing molecular assembly that brings us a step closer to building such a nanoscale processor.
The conceptual hurdles of building a nanoscale computer are still huge. Even if you get a sufficiently powerful nanoscale processor to work, the information to be processed needs to be fed into it and the results read from it, i.e. the input/output devices also would need to be nanosized. So would be the power supply.
Nevertheless, new research potentially shows a novel way of building parallel processors at the atomic level. Researchers in Japan have built a machine assembly consisting of 17 identical molecules of an organic compound called duroquinone (DRQ) which is capable of executing 16 instructions at a time.
"The essence of what we have shown is that a stable radial connection between elements can generate truly parallel connection" Dr. Anirban Bandyopadhyay tells Nanowerk. "A single DRQ molecule is positioned at the center of a circular ring formed by 16 other DRQ molecules, controlling their operation in parallel through hydrogen-bond channels. Each molecule is a logic machine and generates four instructions by rotating its alkyl groups. A single instruction executed by a scanning tunneling microscope (STM) tip on the central molecule can change decisions of 16 machines simultaneously, in four billion ways (416)."
This movie is a 3-D view of 19 simultaneous operations of eight reported nano-machines. 1. Elevator of Stoddart et. al., 2. Rotary fan of Feringa et. al., 3. Nano-toy of Tour et. al., 4. Switch of Fujimura et. al., 5. Bearing of Ross Kelly et. al., 6. Flier of Kuroda et. al., 7. Dual flipper of Shinkai et. al., 8. Link breaker of Branchaud et. al.. Each of these machines has different operational mechanisms and can deliver certain jobs assigned to them.
Bandyopadhyay, a scientists at the International Center for Young Scientists at the National Institute of Materials Science (NIMS) in Tsukuba, Japan, together with his collaborator Dr. Somobrata Acharya, has shown that their device – in what they call “one-to-many” communication – can simultaneously perform 16 operations at once. They reported their findings in the March 11, 2008 online edition of PNAS ("A 16-bit parallel processing in a molecular assembly").
The fundamentals this recent work has been building on were reported by Bandyopadhyay and collaborators in a previous paper in Applied Physics Letters ("Writing and erasing information in multilevel logic systems of a single molecule using scanning tunneling microscope"). There, the scientists showed that a quinone molecule can store two bits of data and they were able to toggle the two bits between 'on' and 'off' states using pulses from a STM.
In the recent work, Bandyopadhyay and Acharya show that their circular assembly of 16 DRQ molecules (the 'execution units') plus a DRQ molecule in the center of the ring (the 'control unit') on a gold surface can be used to facilitate simultaneous one-to-many communication: "When we instructed the molecule at the center of our assembly, the 16 molecules in the ring are instructed at once in a logical way" says Bandyopadhyay. "The concept of simultaneous one-to-many communication could be generalized in building massive supramolecular architectures wherein parallel signal processing could be established."
By applying an electrical pulse from an STM to the central DRQ molecule, the researchers could switch the 'control unit' into any of four different states. Every time they did this, the control unit sent 16 unique instructions simultaneously to the 16 execution units making up the ring. In effect, the chemical changes in the DRQ molecules are used to encode state changes that potentially could be used for computational purposes.
Bandyopadhyay explains that this kind of stable radial connection between elements could be applied to construct any circular massive parallel communication system where the central connecting unit is capable of withstanding multiple communications at a time. "Just connecting radially might not generate similar parallel processing" he says. "The reason is that signal processing to multiple systems at a time generates perturbation in the central connecting unit, surviving which is the key. For example, if one wires 17 transistors in the same design as ours they will never operate in a parallel fashion."
A critical step in developing this concept further will be to demonstrate that the system not only works as a parallel-communication, hub-spoke array but is capable of actually performing parallel computing. Also, in order for this molecular assembly to become a practical nano-computer the researchers must find a way control the central molecule with something way smaller than a STM.
By . Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology (RSC Nanoscience & Nanotechnology) and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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