Showing papers on "Buffer solution published in 2012"

Controlled-pH Tissue Cleanup Protocol for Signal Enhancement of Small Molecule Drugs Analyzed by MALDI-MS Imaging

Abstract: The limit of detection of low-molecular weight compounds in tissue sections, analyzed by matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI), was significantly improved by employing sample washing using a pH-controlled buffer solution. The pH of the washing solutions were set at values whereby the target analytes would have low solubility. Washing the tissue sections in the buffered solution resulted in removal of endogenous soluble ionization-suppressing compounds and salts, while the target compound remained in situ with minor or no delocalization during the buffered washing procedure. Two pharmaceutical compounds (cimetidine and imipramine) and one new protease inhibitor compound were successfully used to evaluate the feasibility of the pH-controlled tissue washing protocol for MALDI-MSI. Enhancement in signal-to-noise ratio was achieved by a factor of up to 10.

Electrocatalytic oxidation of sulphide using a pencil graphite electrode modified with hematoxylin

Abstract: The present study describes a new approach for the investigation of electrocatalytic oxidation of sulphide using a pencil graphite electrode modified with hematoxylin (PGE/HMT). Adsorption procedure was used for the preparation of the modified electrodes. It was observed that PGE/HMT showed a significant electrocatalytic activity toward sulphide oxidation. Cyclic voltammetric studies showed that the peak potential of sulphide shifted from +480 mV at bare PGE to +220 mV at PGE/HMT. The electrocatalytic currents obtained from amperometric measurements at +200 mV versus Ag/AgCl/KCl sat and at pH 8.0 BR buffer solution containing 0.1 M KCl were linearly related to the concentration of sulphide. The calibration graph consisted of a linear segment of 1–200 μM with a detection limit of 0.4 μM (based on 3 s b ). The proposed method was successfully applied to the determination of sulphide in waste waters and was compared with the spectrophotometric method.

Interaction of Bovine Serum Albumin with Ester-Functionalized Anionic Surface-Active Ionic Liquids in Aqueous Solution: A Detailed Physicochemical and Conformational Study

Abstract: Ester-functionalized anionic surface-active ionic liquids (SAILs), 3-methyl-1-(ethoxycarbonylmethyl)imidazolium dodecylsulfate ([C1COOC2C1im][C12SO4]) and 3-methyl-1-(ethoxycarbonylmethyl)pyrrolidinium dodecylsulfate ([C1COOC2C1Py][C12SO4]), were synthesized. The tensiometric profiles demonstrate that, in pure water, the studied SAILs exhibit higher surface activity than the traditional anionic surfactant, sodium dodecyl sulfate (SDS), and cationic SAILs, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and N-dodecyl-N-methylpyrrolidimium bromide (C12MPB), with the same hydrocarbon chain length. The interaction between bovine serum albumin (BSA) and the anionic SAILs in pH 7.4 buffer solution was systematically investigated by various techniques. The results show that the cationic ring has a slight effect on the BSA–SAIL interaction. The binding isotherms of BSA with the SAILs display four characteristic regions with increasing SAIL concentration. The unfolding of BSA occurs in the third region. Fluores...

V2O5/WO3 Mixed Oxide Films as pH-EGFET Sensor: Sequential Re-Usage and Fabrication Volume Analysis

Abstract: A vanadium and tungsten mixed oxide was deposited onto glassy carbon substrates and used as pH sensor in extended gate field effect transistor (EGFET) devices. WO3 at a molar ratio of about 5% was mixed with V2O5 by means of the sol-gel method. The main focus of this investigation was to determine the operation conditions for the best response of the device and to propose the mechanism involved in the sensor response. The use of either original or reused films were employed and the importance of the total volume of the starting solution was also examined. The time response of the V2O5/WO3-pH-EGFET sensor is due to a deprotonation mechanism of vanadium and tungsten oxide, similarly to a discharging capacitor. The loss of protons by the oxide film depends on the time it remains immersed in the buffer solution and this process is accelerated upon raising the pH value. The increase of the films fabrication volume reduces the importance of the changes of the surface charges compared to the charges of the bulk, leading to less sensitive and less stable sensor response. Therefore, the smaller the amount of material used, the better the sensing properties of the device.

Vaterite Synthesis via Gas–Liquid Route under Controlled pH Conditions

Abstract: The purpose of this work was to obtain precipitated calcium carbonate (PCC) particles in polymorphic form of vaterite via gas–liquid route in controlled pH conditions. The effect of CO2 concentration (12.5–100%), feed gas (CO2–air) flow rate, pH, and conductivity of solution upon the PCC particles properties was studied. On the basis of the experimental data, the main factors leading to vaterite formation as major product were established. It was found that the buffer solution has a decisive role in determining polymorphic phase of PCC while CO2 concentration and feed gas flow rate have no significant influence. It was demonstrated that spherical vaterite particles of high purity can be produced under controlled reaction conditions. Also, some considerations on the mechanism of carbonation process were formulated.

Modulating the selectivity by switching sensing media: a bifunctional chemosensor selectivity for Cd2+ and Pb2+ in different aqueous solutions

Abstract: A novel bifunctional fluorescent probe RI, based on rhodamine with isatin, was designed and synthesized. Switching of the selectivity of RI between various metal ions was achieved by judicious choice of sensing media. RI gives a turn-on fluorometric and colorimetric signal toward Cd2+ in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (10 mM, CH3OH–H2O, 4 : 6, v/v, pH 7.6) buffer solution and a turn-on colorimetric signal toward Pb2+ in Tris-HCl (70 mM, CH3OH–H2O, 6 : 4, v/v, pH 7.6) buffer solution. To the best of our knowledge, this is the first example of a chemosensor based on a small molecule that can selectively recognize both Cd2+ and Pb2+ in different sensing systems. Fluorescence imaging of Cd2+ in living cells was also obtained.

Colorimetric sensing of trace UO22+ by using nanogold-seeded nucleation amplification and label-free DNAzyme cleavage reaction

Abstract: In pH 4.4 HAC–NaAC buffer solution at 80 °C, nanogold particles (NG) strongly enhanced the slow, colored reaction of Ag(I)–gallic acid to form nanosilver particles, which exhibited a strong surface plasmon resonance (SPR) absorption peak at 460 nm, but the aggregated nanogold particles (ANG) exhibited a weak enhancement. The increased absorption value at 460 nm was linear to the NG concentration in the range of 3.6–72.5 ng mL−1 Au. In pH 5.5 MES buffer solution at 80 °C, single-stranded substrate DNA and DNAzyme hybridize to form double-stranded DNA (dsDNA). The presence of uranyl (UO22+) resulted in cleavage of the substrate DNA of dsDNA, releasing a short, single-stranded DNA that can be adsorbed onto the NG and protect them from aggregation; those un-adsorbed NG were aggregated to ANG. As the UO22+ concentration increased, more short, single-stranded DNA were released, and more NG were protected by the cleavage of substrate single-strand DNA, so the colored particle reaction and the absorption value at 460 nm enhanced linearly. On those grounds, 0.083–0.67 nmol L−1 UO22+ can be detected rapidly by this colorimetric sensing assay, with a detection limit of 0.04 nmol L−1.

Selective fluorescence sensors for p-phenylenediamine using formyl boronate ester with an assistance of micelles

Abstract: A selective fluorometric approach for detection of p -phenylenediamine (PPD) was fabricated using the alizarin–boronic acid adduct with an assistance of micelles. When Alizarin Red S (ARS) reacted with 4-formylphenylboronic acid (4-FPBA) and yielded the boronate ester adduct (ARS/4-FPBA), the fluorescence emission turned on. However, upon the addition of PPD, the fluorescence intensity of the ARS/4-FPBA adduct decreased as a linear function of PPD concentrations. Enhancements in sensitivity and selectivity of this fluorescence sensor were studied by incorporating the sensor molecule into the hydrophobic core of micelles. The results showed significant improvement in sensitivity and selectivity comparing to the sensor in the buffer solution. Parameters affecting the fluorescence quenching of boronate ester adducts by PPD such as solution pH, 4-FPBA concentration, types of surfactants and surfactant concentrations were investigated. The optimum conditions for the determination of PPD was 2.0 mM cetyltrimethylammonium bromide (CTAB) in 50 mM phosphate buffer solution pH 7.0. The fluorescence intensity of the ARS/4-FPBA adduct in the presence of CTAB was remarkably 11 times as high as that in the buffer solution. The linear working concentration range was found to be 0.03–0.40 mM and the calibration sensitivity was 48 times higher than that from the system containing only buffer solution. Moreover, PPD exhibited the highest calibration sensitivity among the studied primary amines, confirming that the proposed sensor provided high sensitivity and good selectivity for PPD. The proposed sensor was used to determine PPD in spiked water samples satisfactorily.

Glucose/O2 biofuel cell based on enzymes, redox mediators, and Multiple‐walled carbon nanotubes deposited by AC‐electrophoresis then stabilized by electropolymerized polypyrrole

Abstract: In this study, we developed an automated strategy to manufacture an enzyme BFC powered by glucose/O(2). The bioanode consists of GOx enzyme and PQQ redox mediator adsorbed over night on MWCNTs then deposited by means of AC-electrophoresis at 30 Hz and 160 V(p-p) and, finally stabilized by electropolymerized polypyrrole. The biocathode is constructed from LAc enzyme and ABTS redox mediator adsorbed over night on MWCNTs, then electrophoretically deposited under AC-electric field at 30 Hz and 160 V(p-p) and, finally stabilized by electrodeposited polypyrrole. The BFC was studied under air in phosphate buffer solution pH 7.4 containing 10 mM glucose and in human serum with 5 mM glucose addition at the physiological temperature of 37°C. Under these conditions, the maximum power density reaches 1.1 µW · mm(-2) at a cell voltage of 0.167 V in buffer solution and 0.69 µW · mm(-2) at cell voltage of 0.151 V in human serum. Such automated BFCs have a great potential to be optimized, miniaturized to micro and nanoscale devices suitable for in vivo studies.

pH-Dependent SERS by Semiconductor-Controlled Charge-Transfer Contribution

Abstract: With the explosive development of analysis and detecting techniques based on SERS, the further understanding and exploit of the chemical mechanism becomes particularly important. We investigated the contribution of semiconductor to surface-enhanced Raman scattering (SERS) in metal and semiconductor heterostructure consisting of Ag/4-mercaptophenol (MPH)/TiO2. For this, we used the distinctive property, where the band edge position of an oxide semiconductor such as TiO2 is sensitive to the pH value, to control the charge-transfer (CT) contribution. It was found that increasing the pH of the buffer solution negatively shifts the conduction band edge of TiO2, thereby increasing the conductive band electron density at an equilibrium state. Thus, the relative band intensities of Ag/MPH/TiO2 increase in the SERS spectrum, which is attributed to the Herzberg–Teller contribution that occurs via CT. Moreover, because of the slower transport of cations from the pH buffer solution to the surface of TiO2, which resul...

pH- and temperature-responsive behaviors of hydrogels resulting from the photopolymerization of allylated chitosan and N -isopropylacrylamide, and their drug release profiles

Abstract: Allyl glycidyl ether (AGE)-functionalized chitosan (CS-AGE), a macromolecular crosslinker, was synthesized and then copolymerized with N-isopropylacrylamide (NIPAAm) monomer under UV irradiation to produce hydrogels The allylated chitosan and the resulting hydrogels were characterized by 1 H NMR and FT IR, respectively The interior morphologies of the hydrogels were investigated by scanning electron microscopy (SEM) after freeze drying them in the equilibrium state in buffer solution at pH 20 Their swelling kinetics were found to be sensitive to both temperature and pH, so it was possible to modulate the swelling by adjusting the pH or the temperature of the medium containing the hydrogel and the proportion of the CS derivative with respect to the NIPAAm monomer Rheological measurements were utilized to investigate the mechanical properties of the hydrogels The in vitro release profiles of the model drugs methyl orange (MO) and bovine serum albumin (BSA) from the hydrogels were also examined The results revealed that the drug release rate could be tuned by adjusting the pH of the medium and the hydrogel composition

Novel sensor based on carbon paste/Nafion® modified with gold nanoparticles for the determination of glutathione

Abstract: Several problems for the direct electrochemical oxidation of reduced glutathione (GSH) challenge the usage of electroanalytical techniques for its determination. In this work, the electrochemical oxidation of GSH catalyzed by gold nanoparticles electrodeposited on Nafion modified carbon paste electrode in 0.04 mol L−1 universal buffer solution (pH 7.4) is proved successful. The effect of various experimental parameters including pH, scan rate and stability on the voltammetric response of GSH was investigated. At the optimum conditions, the concentration of GSH was determined using differential pulse voltammetry (DPV) in two concentration ranges: 0.1 × 10−7 to 1.6 × 10−5 mol L−1 and 2.0 × 10−5 to 2.0 × 10−4 mol L−1 with correlation coefficients 0.9988, 0.9949 and the limit of detections (LOD) are 3.9 × 10−9 mol L−1 and 8.2 × 10−8 mol L−1, respectively, which confirmed the sensitivity of the electrode. The high sensitivity, wide linear range, good stability and reproducibility, and the minimal surface fouling make this modified electrode useful for the determination of spiked GSH in urine samples and in tablet with excellent recovery results obtained.

Fluorescence detection of adenosine triphosphate in an aqueous solution using a combination of copper(II) complexes.

Abstract: Fluorescent ligands have been designed to form ternary complexes with a Cu(II) cation and phosphates in a buffer solution at physiological pH 7.4. It has been shown that a combination of two different ligands and CuCl(2) allows one to achieve high adenosine triphosphate/adenosine diphosphate, adenosine 5'-monophosphate selectivity, and ratiometric fluorescence sensing, while separately each ligand complex does not have such properties.