AFM Adapted to Measure Adhesion between Carbon Nanotubes and Polymers
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images to directly observe Au-NPs incorporated into the enzyme units. The reconstituted GOx was then assembled on a gold electrode. In the second method, the electrode was first decorated with FADfunctionalized Au-NPs, and this surface was then used to reconstitute the GOx enzyme. Microgravimetric quartz-crystal microbalance measurements indicate a 60% surface coverage for biomaterials prepared by both methods. Cyclic voltammetry studies of the biomaterials prepared by both methods show the glucose electro-oxidation current increases with glucose concentration. Furthermore, the unimolecular electron transfer rate constant that is calculated from the anodic current-density plateau is seven times larger than that measured for native GOx when oxygen is used as the electron acceptor. This indicates an increase in the turnover number for the enzyme that can only be attributed to the use of the Au-NP as the electron-relaying functionality. Control experiments show that the functioning of the bioelectrocatalyst is not affected by the presence of oxygen (a potential electron scavenger) or citric acid (an oxidizable interferant). GREG KHITROV
“Scarring” Produced by Packing of Spherical Particles onto the Surface of a Sphere Packing spherical particles onto the curved surface of a sphere produces “scars,” distinctive high-angle grain boundaries, that are not observed in the packing of spherical particles onto planar surfaces. These scars are observed above a critical system size, and the number of additional defects in these scars increases linearly with the size of the sphere. These findings address a conundrum that has puzzled scientists for almost a century, dating back to theoretical work by J.J. Thomson, who attempted to explain the periodic table of the elements by modeling atoms in terms of rigid shells of electrons. Researchers A. Bausch (Department of Physics, Technische Universität München), M. Bowick (Department of Physics, Syracuse University), and colleagues from Fundamenteel Onderzoek der Materie, Institute for Atomic and Molecular Physics (Amsterdam); the University of Massachusetts; Harvard University; Iowa State University; and Ames National Laboratories reported their experimental studies of packing phenomena in the March 14 issue of Science. Although scientists have theorized and used computational methods to predict minimum energy arrangements for dense packing of repulsive particles on spherical MRS BULLETIN/JUNE 2003
surfaces, the researchers in the present study observed this packing experimentally. The “repulsive particles” were crosslinked polystyrene beads (1 µm in diameter) packed by adsorption on the spherical surfaces of water droplets of various size (e.g., 12 µm radius) formed in an oil bath. The arrangement of particles was imaged using an inverted microscope, and the lattice geometry was analyzed using Delaunay triangulation algorithms for spherical surfaces. Whereas repulsive particles on a planar surface will form a simple lattice of triangles akin to the familiar billiard-ball packing, t
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