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For their ongoing efforts to manufacture ever-smaller technological devices, scientists have recruited some suitably tiny workers: bacteria. According to a report published in the December issue of the journal Nature Materials, proteins produced by microbes living in extreme environments can be used as building blocks for nanoelectronics. The new technique could help researchers assemble electronics 10 to 100 times smaller than those available today.
R. Andrew McMillan of the NASA Ames Research Center and his colleagues isolated a gene from the single-celled organism Sulfolobus shibatae, which typically resides in mud that is close to boiling (see image). The scientists altered the gene so that its protein product self-assembled into a two-dimensional lattice. In addition, certain sites on this lattice, or template, could bind to metal and semiconductor particles. "We cloned, or added, this modified gene segment into a harmless form of E. coli bacteria that rapidly multiplies, producing vast quantities of the new protein," explains team member Chad Paavola. Once the constructed lattices were large enough, the scientists exposed the E. coli bacteria to heat. Because S. shibatae is accustomed to high temperatures, the engineered protein survived, but all the natural E. coli proteins were destroyed. The researchers then placed the crystallized protein template on a silicon wafer and exposed it to a slurry containing gold and semiconductor particles. The minute pieces that attached to the lattice formed semiconductor quantum dots measuring less than five nanometers across and gold nanoparticles one to 10 nanometers wide. Current lithographic techniques for arranging quantum dots into functional patterns are of limited use for objects less than 100 nanometers in size. The new findings thus hold promise for future electronic and photonic devices. Says the study's principal investigator Jonathan D. Trent: "Much of the success of today's electronics industry comes from knowing how to arrange materials in an organized fashion on a silicon substrate, and the prospects of using proteins to improve that process on a nanometer scale is encouraging."