No abstract

This paper describes the development of glucose biosensors based on carbon nanotube (CNT) nanoelectrode ensembles (NEEs) for the selective detection of glucose. Glucose oxidase was covalently immobilized on CNT NEEs via carbodiimide chemistry by forming amide linkages between their amine residues and carboxylic acid groups on the CNT tips. The catalytic reduction of hydrogen peroxide liberated from the enzymatic reaction of glucose oxidase upon the glucose and oxygen on CNT NEEs leads to the selective detection of glucose. The biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents (e.g., acetaminophen, uric and ascorbic acids), avoiding the generation of an overlapping signal from such interferers. Such an operation eliminates the need for permselective membrane barriers or artificial electron mediators, thus greatly simplifying the sensor design and fabrication.Because of the high demand for blood glucose monitoring, significant research and development efforts have been devoted to producing reliable glucose sensors for in vitro or in vivo applications. 1-2 The measurement principle of oxidase-based amperometric biosensors previously relied upon the immobilization of oxidase enzymes on the surface of various electrodes and the detection of the current associated with the redox product in the biological reaction. To increase the selectivity and sensitivity of amperometric biosensors, artificial mediators and permselective coatings are often used in biosensor fabrication. Artificial mediators are used to shuttle electrons between the enzyme and the electrode to allow operation at low potentials. 3-5 This approach can minimize interference with coexisting electroactive species, but the stability and toxicity of some mediators limit their in vivo applications. Permselective membranes are also used to eliminate interference. 6-7 Effective, but incomplete, rejection has been reported in most cases. A mediator-free and membrane-free biosensor was described by Wang's method provides a means for measuring the cathodic current of enzymatically liberated hydrogen peroxide in metal-dispersed carbon paste biosensors. The idea of a mediator-free and membrane-free biosensor based on the reduction of hydrogen peroxide has provided a new approach for biosensor development.Recently, electrochemical properties of carbon nanotubes (CNTs) have been unveiled, and their application toward electrochemical sensors and biosensors has gained interest. [10][11][12][13][14][15][16][17][18][19][20][21][22]

Polycrystalline BiFeO3 nanoparticles (size 80–120 nm) are prepared by a simple sol–gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 μB/Fe at room temperature, in good agreement with theoretical calculations.

WurtziteZnO nanobridges and aligned nanonails have been synthesized by thermal vapor transport and condensation method. The nanobridges have two rows of c-axis ZnO nanorods epitaxailly grown on the edges of the {0001} plane of the ZnO nanobelt. Some variations of the nanobridges have also been observed. The ZnO nanonails, with crystalline cap and small diameter shafts, grow along the c-axis. The shape of the nanonail cap and shaft varies. The nanobridges have very low concentration of indium in the structure and the nanonails are pure ZnO. These materials have potential in applications such as optoelectronics, etc.

Foldable photoelectronics and muscle-like transducers require highly stretchable and transparent electrical conductors. Some conducting oxides are transparent, but not stretchable. Carbon nanotube films, graphene sheets and metal-nanowire meshes can be both stretchable and transparent, but their electrical resistances increase steeply with strain o100%. Here we present highly stretchable and transparent Au nanomesh electrodes on elastomers made by grain boundary lithography. The change in sheet resistance of Au nanomeshes is modest with a one-time strain of B160% (from B21 O per square to B67 O per square), or after 1,000 cycles at a strain of 50%. The good stretchability lies in two aspects: the stretched nanomesh undergoes instability and deflects out-of-plane, while the substrate stabilizes the rupture of Au wires, forming distributed slits. Larger ratio of mesh-size to wire-width also leads to better stretchability. The highly stretchable and transparent Au nanomesh electrodes are promising for applications in foldable photoelectronics and muscle-like transducers.

We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (<20-30 microm in length) exhibiting widths of 20-300 nm and small thicknesses (2-40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene.

Introduction of exogenous DNA into mammalian cells represents a powerful approach for manipulating signal transduction. The available techniques, however, are limited by low transduction efficiency and low cell viability after transduction. Here we report a highly efficient molecular delivery technique, named nanotube spearing, based on the penetration of nickel-embedded nanotubes into cell membranes by magnetic field driving. DNA plasmids containing the enhanced green fluorescent protein (EGFP) sequence were immobilized onto the nanotubes, and subsequently speared into targeted cells. We have achieved an unprecedented high transduction efficiency in Bal17 B-lymphoma, ex vivo B cells and primary neurons with high viability after transduction. This technique may provide a powerful tool for highly efficient gene transfer into a variety of cells, especially the hard-to-transfect cells.

Carbon nanotubes were grown directly on carbon fibers using chemical vapor deposition. When embedded in a polymer matrix, the change in length scale of carbon nanotubes relative to carbon fibers results in a multiscale composite, where individual carbon fibers are surrounded by a sheath of nanocomposite reinforcement. Single-fiber composites were fabricated to examine the influence of local nanotube reinforcement on load transfer at the fiber/matrix interface. Results of the single-fiber composite tests indicate that the nanocomposite reinforcement improves interfacial load transfer. Selective reinforcement by nanotubes at the fiber/matrix interface likely results in local stiffening of the polymer matrix near the fiber/matrix interface, thus, improving load transfer.