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The second nanotech advance has emerged from the union of molecular biology and materials science. Materials science professor Angela M. Belcher and graduate student Daniel J. Solis at Massachusetts Institute of Technology and postdoc Chuanbin Mao at the University of Texas, Austin, spearheaded an effort to make magnetic and semiconducting nanowires using a virus-based scaffold [Science, 303, 213 (2004)]. The group uses an evolutionary screening process to find peptides that can control various features of inorganic nanoparticle nucleation. Then they genetically engineer the pencil-shaped M13 bacteriophage so that the virus's capsid incorporates a specific peptide on the surface of its shaft. The desired inorganic compound nucleates at the peptide sites and becomes ordered onto the virus scaffold. High-temperature annealing removes any organic materials, leaving the inorganic particles to collapse into the space formerly occupied by the virus to form a nanowire. "We're trying to develop this as a general kit to make wires out of many different materials," Belcher tells C&EN. The group has already made single-crystal, semiconducting ZnS and CdS nanowires, as well as ferromagnetic CoPt and FePt nanowires. Belcher also would like to make more complex materials using this general DNA modification method. Her group recently made two different genetic modifications to the same M13 bacteriophage, one at the "eraser" end and one at the "pencil tip" end. They then linked the two ends together with another molecule to form a nanoring [Nano Lett., published online Dec. 16, 2003, http://dx.doi.org/10.1021/nl0347536]. According to Belcher, growing nanowires on viruses allows one to use milder (aqueous, ambient, nontoxic) conditions than required by other nanowire fabrication methods. |
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