An aqueous seed-mediated growth method is adapted to explore the shape transformation of quasi-spherical Au seeds to nanocubes in a direct and continuous manner. Quenching the growth process at varied reaction-duration times and exploring the intermediate products by high-resolution transmission electron microscopy and UV/vis spectroscopy shows an abrupt cuboctahedral-to-nanocube transition at 25-27 nm without any change in the nanoparticle size. The size of the obtained nanocubes remains constant (25-27 nm) until most (>90%) of the cuboctahedral nanoparticles are transformed to nanocubes. At this point, the (25-27 nm) nanocubes initiate further continuous and homogeneous growth until they reach 50-nm Au cubes. These observations are ascribed to a scenario in which the kinetically controlled growth mode of the nanoparticle is significantly affected by the surface self-diffusion of metal adatoms, especially when the adatom's self-diffusion distance is comparable with the nanoparticle's size.
Co-self-assembly of mesostructured silica films from solutions of tetrahydrofuran (THF) and water, silica precursor species, and structure-directing Pluronic P123 block-copolymer molecules is reported with and without conjugated polymer guest species. The solution-phase behavior of the ternary THF-water-P123 system guided the selection of nonequilibrium synthesis conditions that allowed highly ordered 2D hexagonal or lamellar mesostructured silica to be prepared. Dilute water molecules produced in situ by silica condensation were necessary and sufficient to promote P123 self-aggregation into micelles and ultimately liquid crystal-like inorganic-organic mesophases as the THF evaporated. Solid-state twodimensional 13 C{ 1 H} and 29 Si{ 1 H} NMR characterization of the product film materials revealed highly mobile block copolymer components at room temperature and preferential interactions of poly(ethylene oxide) moieties with the silica framework at 260 K. Solution processing in THF permitted highly hydrophobic, high molecular weight, conjugated polymers to be directly coassembled within the mesostructured inorganic-organic host matrices during their formation. The incorporated conjugated polymers exhibited semiconducting properties and enhanced environmental photo-stability that may be exploited in electronic and optoelectronic devices.
We report on the feasibility of cubic Pt nanoparticles (NPs) capped with four representative organic ligands, viz. oleylamine (ODA), 11-mercaptoundecanol, 11-mercaptoundecanoic acid, and benzylmercaptan, for sensing gaseous nonpolar analytes in humid atmospheres. Chemiresistors based on cubic Pt NPs with nonpolar ligands show a very large increase in resistance upon exposure to nonpolar analyte vapors, combined with a low sensitivity to polar analyte vapors, especially to water. The sensing mechanism can be understood in terms of analyte-induced changes in the NP-NP core distance and changes in the permittivity of the medium between the NPs. The sensing capabilities of the Pt NP chemiresistors for nonpolar molecules in highly humid atmospheres are demonstrated by dosing an ODA-capped cubic Pt NP sensor with air mixtures containing low octane concentrations and high humidity levels that are typical for many applications. The simple construction, low cost, stability, fast response, and high sensitivity to nonpolar molecules, together with the low sensitivity to water vapor, are promising features for sensing applications in real confounding atmospheres.
Certain benign breast diseases are considered to be precursors of invasive breast cancer. Currently available techniques for diagnosing benign breast conditions lack accuracy. The purpose of this study was to deliver a proof-of-concept for a novel method that is based on breath testing to identify breast cancer precursors. Within this context, the authors explored the possibility of using exhaled alveolar breath to identify and distinguish between benign breast conditions, malignant lesions, and healthy states, using a small-scale, case-controlled, cross-sectional clinical trial. Breath samples were collected from 36 volunteers and were analyzed using a tailor-made nanoscale artificial NOSE (NA-NOSE). The NA-NOSE signals were analyzed using two independent methods: (i) principal component analysis, ANOVA and Student's t-test and (ii) support vector machine analysis to detect statistically significant differences between the sub-populations. The NA-NOSE could distinguish between all studied test populations. Breath testing with a NA-NOSE holds future potential as a cost-effective, fast, and reliable diagnostic test for breast cancer risk factors and precursors, with possible future potential as screening method.
The use of assemblies of monolayer-capped nanoparticles (MCNPs) to design chemically sensitive resistors (chemiresistors) has two main attributes. [1][2][3][4][5] The first is the presumed ability to synthesize, if not at will then with much control, nearly any type of MCNP one wishes. [6] The second is the ability to control the interparticle distance and uniformity in the films [1,2,6] that affect the background noise, [7] which, eventually, determines the device sensitivity. In addition, MCNP-based chemiresistors are especially simple to prepare, are inherently compatible with conventional silicon electronics processing and readout circuitry, and are therefore miniaturizable and scalable. [1,2] In this class of chemiresistors, the metallic particles provide the electric conductivity and the organic film provides sites for the sorption of analyte (guest) molecules. The presence of well-defined organic spacers (i.e., molecules) allows the interparticle distance to be controlled and, thereby, nearly uniform interparticle distances in the composite films to be obtained. [1,2] To date, MCNP-based chemiresistors were produced from nanoparticles (NPs) with spherical shapes. [1,2] Nevertheless, for many applications the use of spherical MCNPs as base materials for chemiresistors is hindered by two major limitations of their swellability. First, the voids between adjacent spherical MCNPs (30-60% of the total volume of the three-dimensional (3D) assembly) [1] can host analyte molecules during the exposure process, but do not (or hardly) contribute to the swelling-induced sensing signal (Scheme 1A). Second, the interface contacts between adjacent spherical MCNPs, at which analyte molecules adsorb and induce changes in the film, are relatively small compared to the total surface area of an individual spherical MCNP. The relatively small interface contacts could also suppress the efficiency of electron transfer (note that efficient electron transfer increases the signal-to-noise ratio). Herein, we show that 3D films made of cubic NPs [8] capped with organic monolayers provide significantly higher sensitivity towards volatile organic compounds (VOCs) than similar films made of spherical NPs. Our findings are explained in terms of the higher swellability of the cubic MCNP films (Scheme 1B).Polyacrylate-capped cubic Pt NPs and polyvinylpyrrolidone-capped spherical Pt NPs with a characteristic dimension of 6.0 AE 0.4 nm were synthesized by hydrogen [9] and heat [10] procedures, respectively. The polyacrylate and polyvinylpyrrolidone molecules coating the Pt NPs were then exchanged with dodecanethiol (DDT) in a THF/water medium, accompanied by subsequent transfer of the final DDT-capped NPs into toluene or chloroform. Theoretical considerations that are supported by transmission electron microscopy (TEM) analysis at different rotation angles of the TEM grid, which contains the NP assemblies, provided knowledge of the voids between adjacent NPs (see Figure 1). The results indicate that the voids between adjacent DDT-capped spher...
A self-assembly process for the preparation of functional mesoscopically ordered semiconducting polymer-silica nanocomposite thin films is reported. The nanocomposites are prepared by introducing pre-synthesized semiconducting polymers into a tetrahydrofuran (THF)-water homogeneous sol solution containing silica precursor species and a surface-active agent. Depending on the concentration of the surface-active agent, it was possible to prepare materials with three different types of mesostructural order: i) a 2D hexagonal mesophase silica with conjugated polymer guest species incorporated within the hydrophobic cylinders organized in domains aligned parallel to the substrate surface plane; ii) a lamellar mesophase silica with the layers oriented parallel to the substrate surface and the conjugated polymer guest species incorporated in the hydrophobic layers; or iii) an apparent intermediate phase consisting of a mixture of the hexagonal and lamellar phases in addition to worm-like aggregates with no appreciable orientational order. The continuous through-film conductive pathway provided by the intermediate phase has allowed the integration of ordered semiconducting polymer-silica nanocomposites into opto-electronic devices. By comparison, the lamellar mesostructure prevents through-film conduction, with the result that no light emission occurs. Blue-, green-and red-emitting diodes comprising blue-emitting poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), green-emitting poly(9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-(2,19,3)-thiadiazole) (F8BT), and red-emitting poly[2-methoxy-5(29-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEHPPV) confined within the 2D hexagonal silica nanostructure were fabricated with luminances of ca. 3 cd m 22 at 15 V. Device performances provide criteria for optimizing the selection of synthesis chemistries, processing conditions, compositions, and structures, for light-emission properties sought.
Lamellar nanocomposites based on semiconducting polymers incorporated into layered inorganic matrices are prepared by the co-assembly of organic and inorganic precursors. Semiconducting polymer-incorporated silica is prepared by introducing the semiconducting polymers into a tetrahydrofuran (THF)/water homogeneous sol solution containing silica precursor species and a surface-active agent. Semiconducting polymer-incorporated MoS 2 and SnS 2 are prepared by Li intercalation into the inorganic compound, exfoliation and restack in the presence of the semiconducting polymer. All lamellar nanocomposite films are organized in domains aligned parallel to the substrate surface plane. The incorporated polymers maintain their semiconducting properties, as evident from their optical absorption and photoluminescence spectra. The optoelectronic properties of the nanocomposites depend on the properties of both the inorganic host and the incorporated guest polymer as demonstrated by integrating the nanocomposite films into light-emitting diodes. Devices based on polymer-incorporated silica and polymer-incorporated MoS 2 show no diode behaviour and no light emission due to the insulating and metallic properties of the silica and MoS 2 hosts. In contrast, diode performance and electroluminescence are obtained from devices based on semiconducting polymer-incorporated semiconducting SnS 2 , demonstrating that judicious selection of the composite components in combination with the optimization of material synthesis conditions allows new hierarchical structures to be tailored for electronic and optoelectronic applications.
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