Three-Dimensional Waveguides Fabricated in Self-Assembled Photonic Crystals
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el atoms they had introduced into the sample. In the underdoped compound, they found nickel impurities centered in α regions, but found none in β regions. Davis said, “A likely explanation is that nickel atoms are indeed present in other regions. But because these are not superconducting, there is no symmetrical particle-hole scattering to reveal the nickel impurities.” Taken together, the two STM techniques—high-resolution spectral surveys and the use of impurity resonances as local markers of superconductivity—not only show that superconductivity is segregated into discrete domains in underdoped B-2212, but also strongly suggest that this material displays granular superconductivity due to frustrated electronic phase separation, according to the research team. “Since the domains are so close together,” Davis said, “quantum-mechanical Josephson tunneling across the nonsuperconducting regions that separate them is probably what supports the long-range superconducting properties of this material.”
Protein Nanoarrays Developed for Studying Biological Processes Scientists at Northwestern University have utilized the method of dip-pen nanolithography to make arrays of proteins with features more than 1000 times smaller than those used in conventional arrays. This leads to nanoarrays with more than a million times the density of current commercial microarrays. Genetic and proteomic screening with so-called gene chips and proteomic arrays are allowing researchers to peer into the genetic code of individuals and develop leads for important therapeutic agents in the pharmaceutical industry. Current technologies use arrays of either proteins or DNA on the micrometer level as screening tools for drug testing and analyzing DNA, protein–protein interactions, and cell biology. Miniaturizing these arrays could dramatically improve their capabilities. Led by Chad A. Mirkin, director of Northwestern’s Institute for Nanotechnology, the research team combined expertise with Milan Mrksich of the University of Chicago and his group and also showed that the novel arrays could be used to study biological processes such as cell adhesion. This involves discovering and then writing a pattern of proteins that attracts a particular molecule. As reported in the March 1 issue of Science (February 7 issue of the Science Express Web site, http://www.sciencexpress.org), 290
Mirkin’s method of dip-pen nanolithography allowed the researchers to use an atomic force microscope tip as a nanopen to write out a tiny protein-dot array on a gold surface, dots as small as 100 nm in diameter. The gold surface between the dots was processed to prevent it from absorbing target proteins and disturbing the readings. When an array on a chip was exposed to protein targets in solution, the protein on the substrate (16-mercaptohexadecanoic acid, or MHA) bound its complementary proteins (lysozyme and rabbit immunoglobin). The atomic force microscope then read the chip and recorded a match where a change in height was detected.
Three-Dimensional Waveguides Fabrica
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