Bubble Logic
How to shrink computers logically - that is the aim of chemist Prasanna "AP" de Silva and his team at Queens University Belfast who have spent many years pondering logic gates and how to make them from molecules. They hope to instill a sense of logic into their chemistry and perhaps one day build a molecular computer that uses these molecular logic gates in a similar way to the microelectronic logic gates on a silicon chip, but at a far smaller and more information-dense scale. Now, de Silva, graduate student Gareth McClean, and post-doctoral researcher Seiichi Uchiyama, working with Kaoru Iwai of Nara Women's University, have taken another quantum leap towards that goal with the synthesis of tiny nanospheres that can act as a two-input ‘AND’ operator.
"We have shrunk the space needed for computation by conducting a logic operation inside a tiny nanospace with a radius of just 3 nanometers," de Silva told Reactive Reports. In contrast, the smallest known silicon devices (from chip manufacturer, Intel) contain features that are enormous in comparison - at 65 nm across. The QUB and Nara team exploited the self-assembling properties of detergent micelles to create a nanoscopic bubble inside which they could contain a logical molecular system, a fluorescent anthracene group with an attached proton-sensing nitrogen group, and a benzo crown ether molecule that can trap alkali metal ions. The presence of a sodium ion AND a hydrogen ion (proton) therefore provides the right chemistry for this logical anthracene group to fluoresce. 'No glow' can be considered a binary "0", while a 'glow' is a "1". Only the presence of the two inputs fulfils the logical condition of ‘AND’, producing a glowing binary "1". If just protons or sodium ions are present, the condition is not fulfilled and the logical molecule remains zeroed.
"We have been able to make this advance by exploiting the ability of membranes to confine guests," de Silva told us, "In terms of computational miniaturization, 3 nm spheres will be hard to beat." The demonstration of a two-input AND logic operation is not the only possibility, however. Researchers, including de Silva's team, have devised other molecular computational operations, which he suggests might now be handled in a similar way. Ultimately, confining logical molecules in layers or three-dimensional lattices of nanoscopic bubbles might allow a true molecular computer to be built.
This discovery is unique in the world of logic, because it shrinks computation to truly small nanometer dimensions. Molecular-based computation always had this potential since molecules exist on this size scale. "To the best of our knowledge, there has been no demonstration of this until now," adds de Silva, "Soap and computers now have common ground."
de Silva confesses that scientists are stumped at present as to how to connect different nanospheres together to make them truly useful. "A positive direction might be to use living cells themselves as somewhat larger versions of our nanospheres," de Silva told us, "Even though some miniaturization is sacrificed, the possibility of synthetic computing inside a living system is appealing. Of course, there is plenty of natural computing within living systems, so that the possibility is not science fiction at all.
J Am Chem Soc, 2005, in press; http://dx.doi.org/10.1021/ja0513638
http://www.ch.qub.ac.uk/staff/desilva/apds.html
http://koto.nara-wu.ac.jp/kenkyu/Profiles/0003/0000123/prof_e.html
http://en.wikipedia.org/wiki/Logic_gate
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