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pH Sensing (ph + sensing)
Selected AbstractsIon and pH Sensing with Colloidal Nanoparticles: Influence of Surface Charge on Sensing and Colloidal PropertiesCHEMPHYSCHEM, Issue 3 2010Feng Zhang Dr. Abstract Ion sensors based on colloidal nanoparticles (NPs), either as actively ion-sensing NPs or as nanoscale carrier systems for organic ion-sensing fluorescent chelators typically require a charged surface in order to be colloidally stable. We demonstrate that this surface charge significantly impacts the ion binding and affects the read-out. Sensor read-out should be thus not determined by the bulk ion concentration, but by the local ion concentration in the nano-environment of the NP surface. We present a conclusive model corroborated by experimental data that reproduces the strong distance-dependence of the effect. The experimental data are based on the capability of tuning the distance of a pH-sensitive fluorophore to the surface of NPs in the nanometer (nm) range. This in turn allows for modification of the effective acid dissociation constant value (its logarithmic form, pKa) of analyte-sensitive fluorophores by tuning their distance to the underlying colloidal NPs. [source] Functionalized Siloles: Versatile Synthesis, Aggregation-Induced Emission, and Sensory and Device ApplicationsADVANCED FUNCTIONAL MATERIALS, Issue 6 2009Zhen Li Abstract The synthesis of functionalized siloles has been a challenge because of the incompatibility of polar functional groups with the reactive intermediates in the conventional protocols for silole synthesis. In this work, a synthetic route for silole functionalization is elaborated, through which a series of functionalized siloles are successfully prepared. Whereas light emissions of traditional luminophores are often quenched by aggregation, most of the functionalized siloles show an exactly opposite phenomenon of aggregation-induced emission (AIE). The siloles are nonemissive when dissolved in their good solvents but become highly luminescent when aggregated in their poor solvents or in the solid state. Manipulation of the aggregation,deaggregation processes of the siloles enables them to play two seemly antagonistic roles and work as both excellent quenchers and efficient emitters. The AIE effect endows the siloles with multifaceted functionalities, including fluorescence quenching, pH sensing, explosive detection, and biological probing. The sensing processes are very sensitive (with detection limit down to 0.1,ppm) and highly selective (with capability of discriminating among different kinds of ions, explosives, proteins, DNAs, and RNAs). The siloles also serve as active layers in the fabrication of electroluminescent devices and as photosensitive films in the generation of fluorescence patterns. [source] AlGaN/GaN high electron mobility transistor structures for pressure and pH sensingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005B. S. Kang Abstract Nitride High Electron Mobility Transistor(HEMT) structures are excellent candidates for polar liquid detectors, pressure sensors and piezoelectric-related applications. The changes in conductance of the channel of AlGaN/GaN high electron mobility transistor structures during application of both tensile and compressive strain are reported. For fixed Al mole fraction, the changes in conductance were roughly linear over the range up to 2.7 × 108 N.cm,2 , with coefficients for planar devices of ,6.0 +/,2.5 × 10,10 S.N,1 m,2 for tensile strain and +9.5+/,3.5 × 10,10 S.N,1m,2 for compressive strain . The large changes in conductance demonstrate that simple AlGaN/GaN heterostructures are promising for pressure and strain sensor applications. A gateless HEMT structure was also used for sensing different liquids present in the gate region. The forward current showed significant decreases upon exposure of the gate area to solvents (water, acetone) or acids (HCl). Milli ampere changes in the source-drain current are observed relative to the value measured in air ambient . The pH sensitivity is due to changes in net surface charge that affects the relative depletion in the channel of the transistor. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modification of mesostructure base on composition of silica materials and their applications to pH sensing,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2006Eun-Hee Kang Abstract This study induced a chemical combination of fluoresceinamine (FA) and (3-chloropropyl)triethoxysilane (CP-TEOS) in the presence of tetraethyl orthosilicate (TEOS) which is able to maintain the shape of the mesostructure without prior removal of the surfactant. The sol-gel derived silica films were controlled by the reaction time and molar ratios of TEOS and CP-TEOS, and characterized in terms of response to pH, pKa values, effects of oxidation number, leaching, and scanning electron microscopy (SEM) imaging. The conclusions include the effect on molar ratios and the choice of reaction time. The results of this study are summarized as follows: (1) increasing the molar ratio of TEOS, the mesostructure of these films exhibited not only perfect single-crystal morphology but also a hexagonal morphology; (2) the most suitable molar ration in this synthesis is the ratio of 1:1 (the molar ratio of TEOS and CP-TEOS); (3) the reaction time for this system should be controlled at least to over 6,hr in order to maintain high intensity absorbance against a minimum of indicator quantity. Leaching-out is more pronounced for films used directly after preparation and varies for different molar ratios. The long-term implication of leaching-out on sol-gel based pH sensors is discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||