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A "plug and play" approach to building molecular logic units has been developed by chemists at Queen's University Belfast and Kasetsart University and Chulalongkorn University, Bangkok. The team used various spectroscopic techniques, including fluorescence and NMR to monitor their logical constructions. Prasanna "AP" de Silva and QUB colleagues have been working on the development of molecular logic units that could represent the building blocks of a future generation of computational devices. A "wet", chemistry-based computer is still a long way off. However, these systems, which are built from units that can recognise individual molecules and ions and fluoresce with different colours depending on the output of their logical operations have formed the basis of a range of commercial applications. "Rather than making a 'wet' computer, molecules have started entering small spaces to do computing in those locations," de Silva told SpectroscopyNOW. de Silva's research into a fluorescent PET (photoinduced electron transfer) sensor design was used in a portable diagnostic tool, a blood gas analyser, for hospital critical care units and ambulances. The device has sensors for sodium, potassium and calcium and was designed, synthesized and tested in collaboration with scientists at AVL Bioscience Corporation, Roswell, GA, and marketed in the late 1990s. However, one aspect of molecular logic that limits its wider development is the need to use the skills of organic synthetic chemistry. These are powerful techniques, but increasingly in short supply in an age when bio is booming and nano is growing and students have turned to those areas of science in preference to the more traditional fields. Despite the complexities of organic chemistry, data processing in small spaces has continued to grow well thanks to de Silva and others. The primary incentive, aside from fundamental aims, lying in the fact that conventional silicon devices are at least 1000 times bigger than might be their molecular counterparts. Examples of computing within living cells have been demonstrated (M.N. Win and C.D. Smolke, Science 2008, 322, 456). Other examples of molecular computation have been carried out on the surface of plastic beads used in combinatorial chemistry (de Silva et al, Nature Mater, 2006, 5, 787) and even inside tiny soap bubbles, more formally detergent micelles (de Silva et al, J Am Chem Soc, 2005, 127, 8920). Now, de Silva, QUB colleagues Catherine Dobbin and Thomas Vance together with Boontana Wannalerse, are taking a different tack. "This new approach shows a really easy way to make molecular logic gates," de Silva says. The method involves implementing a set of ion-driven molecular logic gates based on tris(2,2-bipyridyl)Ru(II) complexes in turn by arranging the association between off-the-shelf lumophores and receptors in detergent micelles. Previously, each molecular logic gate had to be synthesised using conventional organic synthesis, but de Silva and his colleagues have now shown that molecular logic gates can be self-assembled from components that they simply mix together. They can change the configuration, i.e. the class of logical operation - YES, NOT, OR, AND, PASS 0, and PASS 1 - simply by adding other components. Fundamentally, this means they can build up a toolbox of logic gates from a small set of components without having to construct each "device" from scratch. "This technique is very much 'plug and play'," de Silva told SpectroscopyNOW, "We hope this will encourage a new bunch of researchers (who don't like too much synthesis) to join the efforts to make molecules compute in more and more interesting situations." "All the single-input, single-output Boolean logic operators and two important cases of the double-input, single-output versions can be produced by simple addition of lumophores and receptors into aqueous micellar solutions," the researchers say, "The micellar self-assembly approach is very convenient, though the intensity ratios of the 'high' and 'low' output states deserve improvement in future studies. This approach complements the use of luminescent, but covalently bound, switching systems for the examination of micellar environments." de Silva adds that, it is important to demonstrate simpler ways of achieving molecular logic so that more opportunities arise for conceptual development. Related links: The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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 Units of molecular logic |
