Novel Hexaferrites Show Potential for Microwave Applications
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Stanford Genome Technology Center at Stanford University have introduced a process to detect and potentially identify single DNA molecules labeled with nanoscale gold particles. While other groups have tried to develop such screening technologies using nanopores, Karhanek and colleagues use nanopipettes combined with measurements of electrical activity. They have found that nanopipettes are faster, easier, and less expensive to fabricate than nanopores. The nanopipettes were produced from standard quartz capillary tubes (inner diameter, 0.7 mm; outer diameter, 1.0 mm) that were pulled to a needle point with nanometer-scale openings at the point end. The pulling was accomplished with the aid of a laser-based pipette puller. The diameter of the opening of the nanopipette is ~50 nm. The researchers attached gold particles to DNA molecules to facilitate detection. The 10-nm-diameter nanoparticles were prepared, stabilized with dipotassium bis(p-sulfonatophenyl) phenylphosphine, and bound to 24-mer oligonucleotides. Through a series of experiments, the research team focused on detecting ionic current blockade events caused by the DNA–gold particles flowing through the tip of the nanopipette. This was accomplished by placing the nanopipette, filled with a KCl solution and the nanoparticle–DNA colloid, into a bath containing the KCl solution. One Ag/AgCl electrode was placed in the bath as a reference, and another was placed into the wide end of the nanopipette in contact with the solution. The researchers then monitored changes in current flow between the two electrodes and observed current jumps (blockades) whenever the nanoparticle or the oligonucleotide blocked ionic transport through the opening in the nanopipette. Based on a statistical analysis of the blockade events, the researchers were able to infer structural information of the DNA–gold particles as they flowed through the sensor, including detection of the putative head and tail of the particles. They also observed that the DNA–gold particle often enters the pipette without full translocation. From the experimental data, the researchers said conditions exist for a certain energy profile with energy wells and barriers, causing a trapping and slowing of the molecules during translocation. Karhanek and his colleagues concluded that this detection technique may lead to new versatile methods not only for the detection and identification of DNA molecules, but also for the detection of protein targets. For this purpose, the nanopipette tip could be functionalized with a target’s MRS BULLETIN • VOLUME 30 • MAY 2005
conjugate, said Karhanek. Such experiments may shed light on different conformations of the protein–ligand complex. In more general terms, these techniques may be used to study the dynamics and interactions of various biomolecules with their environment. Not only would this be helpful for technological breakthroughs, said the researchers, but it may also help to understand fundamentals about biological processes. MARKUS J. BUEHLER
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