Showing papers on "Buffer solution published in 2010"

Liposomal apparatus and manufacturing methods

Abstract: The present invention provides apparatus and processes for producing liposomes. By providing a buffer solution in a first reservoir, and a lipid solution in a second reservoir, continuously diluting the lipid solution with the buffer solution in a mixing chamber produces a liposome. The lipid solution preferably comprises an organic solvent, such as a lower alkanol.

Amperometric biosensor for direct blood lactate detection.

Abstract: An amperometric sensor for lactate quantification is presented. The developed biosensor requires only 0.2 U of lactate oxidase, which is immobilized in a mucin/albumin hydrogel matrix. By protecting the platinum surface with a Nafion membrane, typical interference related to negatively charged species such as ascorbic acid has been minimized to practically undetectable levels. Electrochemical properties associated with the Nafion membrane are assessed as a function of Nafion concentration. In a phosphate buffer solution of pH 7.0, linear dependence of the catalytic current upon lactate bulk concentration was obtained between 2 and ∼1000 μM. A detection limit of 0.8 μM can be calculated considering 3 times the standard deviation of the blank signal divided by the sensitivity of the sensor. The lactate biosensor presents remarkable operational stability and sensitivity (0.537 ± 0.007) mA.M−1, where the error is the standard deviation of the slope calculated from the linear regression of the calibration curv...

Electrochemical sensor for 2,4-dichlorophenoxy acetic acid using molecularly imprinted polypyrrole membrane as recognition element

Abstract: An electrochemical sensor based on molecularly imprinted polypyrrole membranes is reported for the determination of 2,4-dichlorophenoxy acetic acid (2,4-D). The sensor was prepared by electropolymerization of pyrrole on a glassy carbon electrode in the presence of 2,4-D as a template. The template was removed by overoxidation at +1.3 V in buffer solution. The sensor can effectively improve the reductive properties of 2,4-D and eliminate interferences by other pesticides and electroactive species. The peak current at -0.78 V is linear with the concentration of 2,4-D from 1.0 to 10 µM, the detection limit is 0.83 µM (at 3σ), and the relative standard deviation is 3.9% (at 5.0 µM of 2,4-D; n = 7). The method has been successfully applied to the determination of 2,4-D in environmental water samples, with recovery rates ranging from 92% to 108%.

A triphenylamine-grafted imidazo[4,5-f][1,10]phenanthroline ruthenium(II) complex: acid-base and photoelectric properties.

Abstract: A new heteroleptic ruthenium(II) complex of [Ru(Hipdpa)(Hdcbpy)(NCS)2]−·05H+·05[N(C4H9)4]+ Ru(Hipdpa) {where Hdcbpy = monodeprotonated 4,4′-dicarboxy-2,2′-bipyridine and Hipdpa = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline} was synthesized and characterized by elementary analysis, standard spectroscopy techniques, and cyclic voltammetry The ground- and excited-state acid−base properties of Ru(Hipdpa) were studied by means of UV−vis absorption spectrophotometric and spectrofluorimetric titrations in 4:1(v/v) Britton-Robinson/dimethylformamide buffer solution The four-step separate protonation/deprotonation processes were found in the ground states, and one of which taking place near the physiological pH range The two observable excited-state protonation/deprotonation processes were found for the Ru(Hipdpa), constituting pH-induced “off−on−off” emission switches The performance of the complexes as photosensitizers in nanocrystalline TiO2-based liquid solar cells containing an ele

Immobilization of Candida antarctica lipase B on Polystyrene Nanoparticles.

Abstract: Polystyrene (PS) nanoparticles were prepared via a nanoprecipitation process. The influence of the pH of the buffer solution used during the immobilization process on the loading of Candida antarctica lipase B (Cal-B) and on the hydrolytic activity (hydrolysis of p-nitrophenyl acetate) of the immobilized Cal-B was studied. The pH of the buffer solution has no influence on enzyme loading, while immobilized enzyme activity is very dependent on the pH of adsorption. Cal-B immobilized on PS nanoparticles in buffer solution pH 6.8 performed higher hydrolytic activity than crude enzyme powder and Novozyme 435.

Selective solid-phase extraction of rare earth elements by the chemically modified Amberlite XAD-4 resin with azacrown ether

Abstract: A selective solid-phase extraction procedure using chemically modified Amberlite XAD-4 with monoaza dibenzo 18-crown-6 ether was investigated for the preconcentration and separation of La(III), Nd(III) and Sm(III) in synthetic solution. Before loading samples on synthesized adsorbent adjust pH 4.5 by suitable buffer solution. The adsorbed rare earth elements were eluted by 2 M hydrochloric acid. Various parameters like preconcentration, breakthrough capacity, flow rate were investigated. The limits of detection ( n = 5) and limits of quantification ( n = 5) for La(III), Nd(III) and Sm(III) were founded 3.9, 4.2 and 7.4 μg L −1 and 13, 15 and 26 μg L −1 , respectively. The eluted metal ions were determined by ICP-AES.

Development of high-κ HoTiO3 sensing membrane for pH detection and glucose biosensing

Abstract: In this paper, we proposed an electrolyte–insulator–semiconductor (EIS) device incorporating a high-κ HoTiO 3 sensing membrane deposited on Si substrates through co-sputtering for pH detection and glucose biosensing. X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy were used to investigate the structural and morphological features of these films annealed at various annealing temperatures. We found that the EIS device fabricating a high-κ HoTiO 3 sensing membrane annealed at 900 °C exhibited a higher sensitivity of 59.5 mV/pH (in the solutions from pH 2 to pH 12), a lower hysteresis voltage of 2.2 mV (in the pH = 7 → 4 → 7 → 10 → 7), and a smaller drift rate of 0.47 mV/h (in the pH 7 buffer solution) than those of the other annealing temperatures. These results are attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based glucose biosensor incorporating a high-κ HoTiO 3 sensing membrane annealed at 900 °C allowed the potentiometric analysis of glucose, at concentrations ranging from 2 to 8 mM, with a sensitivity of 7.94 mV/mM.

Redox properties and catalytic activity of surface-bound human sulfite oxidase studied by a combined surface enhanced resonance Raman spectroscopic and electrochemical approach.

Abstract: Human sulfite oxidase (hSO) was immobilised on SAM-coated silver electrodes under preservation of the native heme pocket structure of the cytochrome b5 (Cyt b5) domain and the functionality of the enzyme. The redox properties and catalytic activity of the entire enzyme were studied by surface enhanced resonance Raman (SERR) spectroscopy and cyclic voltammetry (CV) and compared to the isolated heme domain when possible. It is shown that heterogeneous electron transfer and catalytic activity of hSO sensitively depend on the local environment of the enzyme. Increasing the ionic strength of the buffer solution leads to an increase of the heterogeneous electron transfer rate from 17 s−1 to 440 s−1 for hSO as determined by SERR spectroscopy. CV measurements demonstrate an increase of the apparent turnover rate for the immobilised hSO from 0.85 s−1 in 100 mM buffer to 5.26 s−1 in 750 mM buffer. We suggest that both effects originate from the increased mobility of the surface-bound enzyme with increasing ionic strength. In agreement with surface potential calculations we propose that at high ionic strength the enzyme is immobilised via the dimerisation domain to the SAM surface. The flexible loop region connecting the Moco and the Cyt b5 domain allows alternating contact with the Moco interaction site and the SAM surface, thereby promoting the sequential intramolecular and heterogeneous electron transfer from Moco via Cyt b5 to the electrode. At lower ionic strength, the contact time of the Cyt b5 domain with the SAM surface is longer, corresponding to a slower overall electron transfer process.

The liquid-junction potentials between some buffer solutions in methanol and methanol-water mixtures and a saturated KCl solution in water at 25°†

Abstract: The determination of the liquid-junction potential at the interface of an oxalate and a succinate buffer solution of known pH* in water, methanol or a methanol-water mixture and a saturated KCl solution in water at 25° is described. When the pH* of such a solution is measured by means of a pH meter standardized by an aqueous standard solution, this liquid-junction potential causes an error of over 2 pH* when the methanol content of the solution is high.

Carbon Paste Gold Nanoparticles Sensor for the Selective Determination of Dopamine in Buffered Solutions

Abstract: �1 universal buffer solution pH 7.4 is introduced. The sensor is based on a carbon paste CP electrode modified with gold nanoparticles. In a mixture of DA, AA, and UA, the sensor shows high selective response toward DA and no response for AA or UA. The effect of various experimental parameters including time of deposition of gold nanoparticles on the CP electrode, pH, and scan rate on the voltammetric response of DA was investigated. At the optimum conditions, the concentration of DA was determined using differential pulse voltammetry in a linear range of 1.0 10 �7 to 5.0 10 �6 mol L �1 and 5.0 10 �6 to 1.3 10 �4 mol L �1 with correlation coefficients of 0.9995 and 0.9988 and a detection limit of 5.9 10 �9 and 8.2 10 �8 mol L �1 , respectively. The modified electrode can be used for the determination of DA spiked into human serum samples, and excellent recovery results were obtained over a wide concentration range of DA. Moreover, validation parameters, such as reproducibility, sensitivity, and recovery were evaluated successfully in the determination of DA in diluted human urine.

Functionalized manganese-doped zinc sulfide core/shell quantum dots as selective fluorescent chemodosimeters for silver ion

Abstract: Zinc sulfide quantum dots doped with Mn(II) ions and coated with a shell of zinc sulfide were prepared, and their surface was modified with iminodiacetic acid to form a QDs-conjugate (QDs-IDA). Such modification effectively improves the water-solubility and luminescence quantum yield of the quantum dots. The optical properties and structural features were characterized by photometry, 1H NMR and fluorescence spectroscopy. The results displayed that QDs-IDA selectively respond to Ag (I) ion in phosphate buffer solution (pH 7.3) in quenching the fluorescence of QDs-IDA. A good linear relationship exists in the concentration range from 5.0 × 10−7 mol·L−1 to 4.5 × 10−6 mol·L−1 and the detection limit is 2.6 × 10−7 mol·L−1. The sensing mechanism was assumed to result from complex formation between the iminodiacetic acid of QDs-IDA and silver (I) ion which promoted photo-induced electron transfer.

Water‐soluble hyperbranched polyelectrolytes with high fluorescence quantum yield: Facile synthesis and selective chemosensor for Hg2+ and Cu2+ ions

Abstract: New water-soluble hyperbranched polyfluorenes bearing carboxylate side chains have been synthesized by the simple "A2 + B2 + C3" protocol based on Suzuki coupling polymerization. The linear polyfluorene analogue LPFA was also synthesized for comparative investigation. The optical properties of the neutral precursory polymers in CHCl 3 and final carboxylic-anionic conjugated polyelectrolytes in buffer solution were investigated. The obtained hyperbranched polyelectrolyte HPFA2 with lower content of branch unit (2%) showed excellent solubility and high fluorescence quantum yield (Φ F = 89%) in aqueous solution. Fluorescence quenching of HPFA2 by different metal ions was also investigated, the polyelectrolyte showed high selectivity for Hg 2+ and Cu 2 , ions relative to other various metal ions in buffer solution. The Stern-Volmer constant K sv was determined to be 0.80 × 10 6 M -1 for Hg 2+ and 3.11 × 10 6 M -1 for Cu 2+ , respectively, indicating the potential application of HPFA2 as a highly selective and sensitive chemosensor for Hg 2+ and Cu 2+ ions in aqueous solution.