Optical Transistor Developed with Single Molecule
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Recently, however, R. Chakrabarty at the Desert Research Institute in Reno and the University of Nevada, M.A. Garro of the Desert Research Institute in Reno and Harvard University, J.G. Slowik of the University of Toronto, E.S. Cross of Boston College, T.B. Onasch of Aerodyne Research, Inc. in Billerica, Mass., and their colleagues have observed ensembles of cluster-dilute soot FAs with much lower Df values, in the range of 1.2–1.5. As reported in the June 12 issue of Physical Review Letters (DOI: 10.1103/PhysRevLett. 102.235504; #235504), Chakrabarty and co-researchers used a pre-mixed etheneoxygen flame set-up that allowed them to vary the fuel-to-air equivalence ratio, φ, from 2.3 to 5.0. After removing soot particles larger than 5 μm from the sample with an impactor, the particles were bipolarly charged with a neutralizer, and then
directed to two in-series electrostatic classifiers (ECs), which are widely used for particle sizing and operate with a combination of viscous and electrostatic force to select particles with a combination of charge and electrical mobility diameter, Dm. The researchers said that this morphology segregation technique is based on the higher likelihood for more elongated particles becoming doubly charged than compact particles because less energy is required to add a second charge at a larger distance than at a short one. Constituting about 3% of the total submicron particle sample and following a Gaussian distribution with a peak Dm of about 460 nm, elongated FAs were impacted onto clear polycarbonate filters for scanning electron microscopy (SEM) analysis. Samples were coated with 1 nm Pt to prevent aerosol charging during SEM. The
researchers imaged about 150 doublycharged FAs for each φ and corrected for the screening effect of 3D particles projected onto two dimensions. Image analysis showed a monotonic decrease in Df from 1.51 to 1.20 as φ increases from 2.3 to 3.5, which the researchers explained by suggesting that the electric field inside the flame causes a partial alignment of aggregates with a dipole moment and nonBrownian diffusion of charged monomers during the aggregation process. Df should approach unity in the limit of vanishing Brownian motion. The researchers said, “If the electrostatic force hypothesis can be verified, it may be possible to control the fractal dimension and associated properties of soot through application of a static electric field.” STEVEN TROHALAKI
Surface-Modified Mesoporous Silica Nanoparticles Serve as Drug Carrier System
As reported on July 2 in the online issue of Nano Letters (DOI: 10.1021/nl901589y), the research team created mesoporous silica nanoparticles with hyperbranched PEI conjugated to the surface. In order to design a cancer-targeting system, folic acid moieties, a ligand for a cell surface receptor that is over-expressed in cancer cells, were covalently attached to the PEI layer. By incubating nanoparticles with fluorescent dyes, delivery to cells could easily be monitored by confocal microscopy. Two different fluorescent dyes
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