Bioelectronic Nanodevices Fabricated on Live Bacteria
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mine the average grain size after crystallization. This could not be done with conventional JMAK analysis because it gives an overall crystallization rate wherein the nucleation and growth rates are coupled. Armed with the ability to determine the rates of nucleation and growth independently, the researchers found them to be constant. By plugging these values into a mathematical expression from the JMAK theory, the researchers found that the experimentally measured grain sizes and the mathematical predictions agree over a broad range of temperatures. This method can be used in practical applications to control grain size and materials properties that are strongly related to microstructure. TAO XU
plastically by GB accommodation (e.g., GB sliding) becomes harder, due to the reduction of the GB sliding and the initialization/emergence of dislocations along the GB. The researchers also performed high-resolution electron microscope (HREM) experiments on Ni nanocrystals after shock-loading at 40 GPa. Ni was used for the experiments because Ni and Cu are fcc materials with similar shock impedances, but Ni has a larger stacking fault energy. The dislocation activity is clearly seen by HREM inside the grains, in excellent agreement with the MD simulation results. FENGTING XU
Shock-Loading Strengthening Mechanism of Nanocrystalline Materials Revealed
Electrically percolating clusters of metal nanoparticles are ideal materials for electronic nanodevices because interparticle current occurs by single-electron transport. The negative surface charges of microorganisms such as viruses, yeasts, and bacteria, make them attractive scaffolds for templating metal nanoparticles. Now, researchers from the University of Nebraska–Lincoln have developed a method for building hybrid bioelectronic devices using gold nanoparticles and live bacteria. Furthermore, a biological response is used to control the electrical response of the devices. As reported in an article published in the October 21 issue of Angewandte Chemie, International Edition (p. 6668; DOI: 10.1002/ anie.200501711), V. Berry and R.F. Saraf deposited the gram-positive bacteria Bacillus cereus on a silica substrate containing linear gold electrodes 7 μm apart, 10 mm long, and coated with poly(L-lysine) (PLL). Filtration and ultracentrifugation were used to extract from culture similar-sized bacteria—about 4–6 μm in length and 0.8–1.0 μm in diameter. Typically, about 10 bridges formed along a pair of electrodes, which were 10 mm long, with a typical bridge composed of two bacteria. The researchers then immersed the bacteria-deposited chip in a solution containing PLL-coated gold nanoparticles (diameter = 30 nm). Berry and Saraf said that the deposition of the gold nanoparticles, regulated simply by time, is highly selective with formation of a gold monolayer only on the negatively charged bacterial surface, because both the nanoparticles and the substrate are positively charged. The negatively charged teichoic acid (a polyelectrolyte on the bacterium surface) wraps the part
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