Indium oxide (In 2 O 3 ) has been used widely for ultra-sensitive toxic gas (such as NO 2 1 and NH 3 2 ) detectors, transparent conductors, 3 solar cells, and optoelectronic devices. 4 It is anticipated that low-dimensional In 2 O 3 may exhibit some unique properties, including novel optical behaviors. 5,6 Although various types of In 2 O 3 , including 2D (i.e., thin films) 7,8 and 1D (i.e., nanowires) 9-11 structures, have been extensively prepared and investigated, few reports were concentrated on In 2 O 3 quantum dots (0D). 12,13 Synthesis and study of high-quality and monodisperse In 2 O 3 nanocrystals (NCs) as 0D quantum-confined materials are still essential and significant. In this communication, we report our synthesis of single-crystal, quasi-monodisperse In 2 O 3 NCs, as well as the optical observation from these NCs.All of the chemicals were used as received from Aldrich without further purification. In a typical experiment, 0.40 mmol of indium acetate (99.99%), 0.55 mL of oleylamine (70%), and 0.60 mL of oleic acid (90%) were combined with 7.0 mL of hexadecane (>99%) in a three-neck flask equipped with a condenser. The system was vacuumed at room temperature and at 110°C for a while, respectively, to form a clear light-green solution. At 110°C , 1.45 mmol of trimethylamine N-oxide (TMNO, 98%) was subsequently introduced into this vigorously stirred hot mixture under an argon stream. The temperature of this system was then increased to 120°C, where it remained for 1 h under agitation and argon protection. The color of the solution gradually turned lightyellow. The temperature was further increased to 290°C at a rate of 10°C/min for an additional 35 min reflux. The mixture was clear-brown during the first 5 min at 290°C, and subsequently changed to a yellow turbid slurry during the following 25 min, and finally turned clear again. These colloids were cooled to room temperature by quickly removing the heating source, and then isolated by adding a sufficient amount of ethanol and separating with centrifugation. The yielded precipitate was redispersed in hexane followed by centrifugation to remove the very small amount of insoluble aggregates. The morphology and phase structure were evaluated using a transmission electron microscope (TEM) (JEOL 2010) and an X-ray diffractometer (XRD) (Philips X-pert system), respectively. We realized that the ratio of oleic acid and oleylamine was a key factor to form In 2 O 3 NCs. Oleic acid without oleylamine and TMNO would not result in any NCs; if TMNO with oleic acid were introduced into the reaction without oleylamine, only indium hydroxide would form according to the results of our XRD analyses; whereas a high content of oleylamine without oleic acid and TMNO would make the NCs rapidly grow and aggregate. We also realized that the TMNO acts as not only a sole oxidizing agent. In addition, it was determined that the reaction temperature is another important parameter which affects the morphology and size of In 2 O 3 NCs. The lower the reaction temperature, the sma...
This paper describes the preparation and optimization of the analytical properties of fluorescence-based submicrometric chloride ion sensing lipobeads. Fluorescence sensing lipobeads are polystyrene nanoparticles that are coated with a phospholipid membrane that contains a fluorescent indicator for a targeted analyte. In this study, the halide-specific fluorescence dye, lucigenin, was immobilized into the phospholipid membrane of the lipobeads to enable chloride ion detection. The fluorescence intensity of lucigenin decreases with increasing chloride ion concentration due to dynamic quenching. Lipobeads that contained only lucigenin were ineffective as chloride ion sensors due to poor partition of the water-soluble lucigenin molecules into the phospholipid membrane and high leakage rate of immobilized lucigenin molecules to the aqueous solution. To stabilize the chloride ion sensing lipobeads we coimmobilized hexadecanesulfonate molecules into the phospholipid membrane. The formation of ion pairs between hexadecanesulfonate and lucigenin decreased the hydrophilicity of the dye, increased its partition rate into the membrane, increased the brightness of the particles, and significantly decreased the leakage rate of the hydrophobic ion pair from the membrane to the solution. To further improve their chloride ion sensitivity, we also immobilized the chloride ionophore [9] mercuracarborand-3 into the lipobead membrane. The study resulted in a unique submicrometric chloride ion sensor, which is suitable for chloride ion measurements in biological fluids.
This paper describes the preparation for the first time of lipobead-based micrometric fluorescence biosensors and the optimization of their analytical properties. The study focused on the well-established urea biosensors as a model system. Fluorescence-sensing lipobeads were prepared by coating carboxyl-functionalized silica microspheres with phospholipids. The enzyme urease and the pH indicator fluorescein-5-thiosemicarbazide were then attached covalently to the phospholipid membrane of the lipobeads. Urease converts urea to ammonia, which results in a pH increase in the analyte solution and to a urea concentration-dependent increase in the fluorescence intensity of the sensing lipobeads. Previous fluorescence-sensing lipobeads were synthesized by coating polystyrene particles with a phospholipid membrane. The membrane was physically attached to the particles and the fluorophores were entrapped in the membrane. In this study, we prepared improved fluorescence-sensing lipobeads by utilizing covalent chemistry to bind the phospholipid membrane to the silica particles and the fluorophores to the membrane. This led to improvement in the stability of the newly developed urea-sensing lipobeads compared to previously developed miniaturized fluorescence biosensors.
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