Electrospun single-crystal MoO 3 nanowires for biochemistry sensing probes
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Single-crystal MoO3 nanowires were produced using the electrospinning technique. High-resolution transmission electron microscopy revealed that the one-dimensional nanostructures are 10–50 nm in diameter, on the order of 1–2 m in length, and have the orthorhombic MoO3 structure. The structure, crystallinity, and sensoric character of these electrostatically processed nanowires are discussed. It has been demonstrated that the nonwoven network of MoO3 nanowires exhibits an order of magnitude higher sensitivity compared with that of a sol-gel based sensor. This is promising for use of the nanowire sensors in nanomedicine.
I. INTRODUCTION
One-dimensional metal oxides are the focus of current research efforts in nanotechnology, as they promise improved electro-optical, electrochromic, catalytic, and gas-sensing properties. The large surface area-to-volume ratio of nanofibers and nanowires suggest improvement of adsorption and reaction rates of gas-sensitive materials. Electrospinning is a novel nanomanufacturing technique used to process metal oxide nanofiber networks. Titanium dioxide was among the first metal oxides that was processed by means of electrospinning into composite nanofibers.1 Titania sol-gel was directly added to an alcohol solution containing polyvinylpyrrolidone (PVP) and was electrospun to form nonwoven mats. Polycrystalline metal oxide nanofibers were produced by a heat treatment in air.1 Another group combined the methodology for forming mesoporous TiO2 with electrospinning to produce mesoporous titanium dioxide fibers.2 More recently, long titania nanofibers and those modified with erbium oxide were fabricated by electrospinning, followed by thermal pyrolysis.3 Pure nanofibers of cobalt oxide, nickel oxide, copper oxide, manganese oxide, zinc oxide, zirconium oxide, and cerium oxide have been synthesized by electrospinning mixtures of polyvinylacetate with metal oxide precursors.4 Other groups have also reported the synthesis of V2O5,5 magnesium titanate,6 p-type palladium oxide,7 nickel titanate,8 and Ru-doped titanium dioxide.9 The common characteristic for all published work on electrospun metal oxide nanofiber formation is the polycrystalline grain morphology seen
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0353 2904
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 11, Nov 2006 Downloaded: 14 Mar 2015
along the decomposed polymer frame of the heat-treated composite fibers. Our work, however, has focused on the breakthrough synthesis of single crystal metal oxide nanowires for gas-sensing applications through electrospinning.10 There are several reasons that single-crystal nanowires are expected to perform better than their polycrystalline counterparts as far as their gas-sensing properties are concerned. Semiconducting oxides exhibit a strong affinity to specific compounds as a function of their polymorphic structure or crystallographic arrangement.11 The selectivity of a sensor to a specific gas or a class of gases ha
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