Cellular Uptake of Functionalized Carbon Nanotubes Shown to be Energy-Dependent
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and AlB2-type superlattices after adding oleic acid…and into NaZn13- or cuboctahedral AB13-type BNSLs after the addition of dodecylamine or TOPO [tri-n-octylphosphine oxide], respectively.” The researchers said that entropic (i.e., space-filling or packing-density factors), as well as van der Waals, steric, and dipolar forces also stabilized the BNSL structures.
Integrated Optical Ring Resonator Demonstrated as a HighSensitivity Biosensor Over the last decade, optical biosensors have become increasingly indispensable
tools in the life sciences, particularly in the area of drug research. These sensors need to be simple, reliable, and able to detect and identify extremely low concentrations of biological molecules. In an article in the December 15 issue of Optics Letters (p. 3344), Alex Ksendzov and Ying Lin of the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., report the demonstration of a new optical biosensor based on a ring resonator that is able to detect concentrations of a test protein as low as 0.1 nM. State-of-the-art optical biosensors are based on “whispering gallery” modes, which guide light along the surface of a
Electronic Carriers Cross Si-Bound Alkyl Monolayers in Two Ways In order to uncover whether organic molecules can be used to pass electrical current, researchers first need to understand how electrons pass through molecules. “To answer this question,” said David Cahen of the Department of Materials and Interfaces at the Weizmann Institute of Science in Israel, “we need to design, build, and use a system that is sufficiently well controlled so that we can be sure that we are measuring what we think we are measuring.” Cahen, collaborating with an international group of researchers, has built such a system and has shown that electrons pass through the system by two different mechanisms, switching from one to the other depending on how much voltage is applied and on the length of the molecules. As reported in the December 31, 2005, issue of Physical Review Letters (DOI: 10.1103/PhysRevLett.95.266807; #266807) the researchers—Cahen, T. Boecking of the University of New South Wales in Australia, C.K. Chan of Princeton University, and colleagues—studied a system of Si-C linked alkyl monolayers sandwiched between a metal (Hg) and semiconductor (n-Si). They discovered that at low forward-bias voltages, the electrons behave quasi-classically, and the temperaturedependence of the current suggests that current is limited by thermionic emission over a barrier in the semiconductor. At higher forward-bias voltages, the electrons behave as waves, and the dependence of the current on the length of the molecules suggests that current is limited by tunneling through the molecules. The researchers said that the longer the molecules, the lower the voltage at which the molecules start to control the current (see Figure 1). Control samples of monolayers on silicon were characterized using both photoemission and other spectroscopies as well as advancing water contact angle (CA). Only samples with CA > 110º on
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