Showing papers on "Buffer solution published in 2021"

Enhancing pH Sensors Performance of ZnO Nanorods With Au Nanoparticles Adsorption

Abstract: In this work, the sensing membrane of extended-gate field-effect-transistor (EG-FET) sensor with zinc oxide (ZnO) nanorods (NRs) and Au adsorbed on ZnO NRs were fabricated by hydrothermal method and DC magnetron sputtering. The Pt sheet as a reference electrode, put in sensing membrane and reference electrode to defferent pH valuse buffer solution for linearity and sensitivity analysis. Results showed the both of the ZnO based EG-FET pH sensors exhibited high linearity and sensitivity, and Au-adsorbed exhibited significantly improved sensing performance, the average voltage sensitivity and average current sensitivity of the ZnO NRs based EG-FET sensor was 24.67 mV/pH and $21.4~\mu \text{A}$ /pH, and linearity was 0.986 and 0.994, whereas that of the Au-adsorbed ZnO NRs based EG-FET pH sensor was 76.75 mV/pH and $45.66~\mu \text{A}$ /pH with a linearity of 0.990 and 0.980.

A pyrene-containing Schiff base fluorescent ratiometric probe for the detection of Cu2+ in aqueous solutions and in cells

Abstract: A highly selective and sensitive fluorescent ratiometric probe (1) based on pyrene-containing Schiff base for the dection of Cu2+ was synthesized. In acetonitrile–HEPES buffer solution (20.0 mM HEPES, 8:2, v/v, pH 7.4), only Cu2+, out of tested common cations, could induce the aggregation of probe 1. Fluorescence analysis showed that the excimer emission band of pyrene groups of probe 1 appeared and gradually increased with the addition of Cu2+. The fluorescent intensity ratio of excimer and monomer (I470/I409) of probe 1 increased 27.8-fold upon the addition of one equiv. of Cu2+ with a detection limit of 20.2 nM (1.28 ppb). The addition of Cu2+ also induced obvious color change and the characteristic peaks of pyrene excimer in UV–vis spectrometra of the relutant solution. Results from the Job plot, metal-binding fluorescent titration, mass spectra experiments and density functional theory calculations indicated a binding ratio of 2:1 (probe 1: Cu2+). In addition, probe 1 showed good potential as a fluorescent visualizing probe for the detection of Cu2+ in living GS cells of epinepheluscoioides.

A Fluorescence Switching Sensor for Sensitive and Selective Detections of Cyanide and Ferricyanide Using Mercuric Cation-Graphene Quantum Dots.

Abstract: This study aims to use graphene quantum dots (GQDs) as a fluorescence switching sensor (turn on-off) for the simultaneous detection of cyanide (CN-) and ferricyanide [Fe(CN)6]3- in wastewater samples The GQDs were synthesized by pyrolyzing solid citric acid The intrinsic blue color of the solution was observed under ultraviolet irradiation The fluorescence spectrum was maximized at both excitation and emission wavelengths of 370 and 460 nm, respectively The fluorescence intensity of GQDs decorated with Hg2+ (turn-off mode as the starting baseline) could be selectively turned on in the presence of CN- and once back to turn-off mode by [Fe(CN)6]3- The fluorescence switching properties were used to develop a fluorescence turn-on-off sensor that could be used to detect trace amounts of CN- and [Fe(CN)6]3- in water samples For highly sensitive detection under optimum conditions (Britton-Robinson buffer solution in the pH range of 80-90, linearity ranges of 50-150 μM (R 2 = 09976) and 100-500 μM (R 2 = 09994), respectively, and detection limits of 310 and 948 μM, respectively), good recoveries in the ranges of 8589-11266% and 8488-11392% for CN- and [Fe(CN)6]3-, respectively, were recorded The developed methods were successfully used for the simultaneous and selective detection of CN- and [Fe(CN)6]3- in wastewater samples obtained from local municipal water reservoirs

Graphitic carbon nitride embedded-Ag nanoparticle decorated-ZnWO4 nanocomposite-based photoluminescence sensing of Hg2+

Abstract: The adverse effects of the advancement of civilization have damaged the environment significantly by heavy metal ion toxicity, empoisoning soil, water, food, etc. In this work, Ag loaded metal tungstate–organic framework-based nanomaterials (g-C3N4/Ag/ZnWO4) which can generate more and more oxygen defects have played a crucial role in detecting selective toxic metal ions in solution. The PL intensity of the samples increases with compositing ZnWO4 with g-C3N4 and Ag, as the recombination of excited electrons with the holes at the oxygen vacancy sites increases. Here, a novel strategy has been adopted to develop a nanocomposite assembly of Ag-loaded ZnWO4 nano-rods with π conjugated sp2 hybridized g-C3N4 for fluorescence detection of Hg2+. The prepared nanocomposites have displayed great fluorescence catalysis for Hg2+ sensing in terms of selectivity, sensitivity, activity, and reaction kinetics. A linear relationship in the range of 0 nM to 2 μM has been obtained for the detection of Hg2+ in a buffer solution of pH = 7.2 (phosphate buffer) by the fluorophore g-C3N4/Ag/ZnWO4 and the minimum detection limit was found to be 0.23 nM. Furthermore, the synthesized nanocomposites were applied for Hg2+ detection in few real samples (pond water, sewage water, etc.), signifying their potential application in routine Hg2+ analysis. The probable mechanistic pathway for the sensing of Hg2+ by grafting the metal ion has also been studied in detail. Based on this mechanism an electronic computing system using an Implication circuit device has been constructed from the molecular information processing and a probable fluorescence mechanism (Jablonski diagram) was explored in which the material was found to possess some room-temperature phosphorescence (RTP).

A Graphene-Based Enzymatic Biosensor Using a Common-Gate Field-Effect Transistor for L-Lactic Acid Detection in Blood Plasma Samples

Abstract: Lactate is an important organic molecule that is produced in excess during anaerobic metabolism when oxygen is absent in the human organism. The concentration of this substance in the body can be related to several medical conditions, such as hemorrhage, respiratory failure, and ischemia. Herein, we describe a graphene-based lactate biosensor to detect the concentrations of L-lactic acid in different fluids (buffer solution and plasma). The active surface (graphene) of the device was functionalized with lactate dehydrogenase enzyme using different substances (Nafion, chitosan, and glutaraldehyde) to guarantee stability and increase selectivity. The devices presented linear responses for the concentration ranges tested in the different fluids. An interference study was performed using ascorbic acid, uric acid, and glucose, and there was a minimum variation in the Dirac point voltage during detection of lactate in any of the samples. The stability of the devices was verified at up to 50 days while kept in a dry box at room temperature, and device operation was stable until 12 days. This study demonstrated graphene performance to monitor L-lactic acid production in human samples, indicating that this material can be implemented in more simple and low-cost devices, such as flexible sensors, for point-of-care applications.

Optical pH Sensor Based on Immobilization Anthocyanin from Dioscorea alata L. onto Polyelectrolyte Complex Pectin-Chitosan Membrane for a Determination Method of Salivary pH.

Abstract: A simple optical pH sensor based on immobilization, Dioscorea alata L. anthocyanin methanol extract, onto a pectin–chitosan polyelectrolyte complex (pectin–chitosan PEC), has been successfully fabricated. The optical pH sensor was manufactured as a membrane made of pectin–chitosan PEC and the extracted anthocyanin. This sensor has the highest sensitivity of anthocyanin content at 0.025 mg/L in phosphate buffer and 0.0375 mg/L in citrate buffer. It also has good reproducibility with a relative standard deviation (%RSD) of 7.7%, and gives a stable response at time values greater than 5 min from exposure in a buffer solution, and the sensor can be utilized within five days from its synthesis. This optical pH sensor has been employed to determine saliva pH of people of different ages and showed no significant difference when compared to a potentiometric method.

Mechanochemical synthesis, thermoanalytical study and characterization of new multicomponent solid forms of norfloxacin with saccharin

Abstract: Cocrystallization is a very efficient strategy to improve the physicochemical properties of bioactive agents. A new norfloxacin (NOR)–saccharin cocrystal and a cocrystal–solvate were synthesized through the mechanochemical method (neat and liquid-assisted grinding), and the characterization was performed by thermal analysis (TG–DTA, DSC and DSC microscopy), infrared vibrational spectroscopy and powder X-ray diffraction. Moreover, solubility experiments carried out in water and buffer solutions (pH 3.0, 6.1 and 8.5) showed that norfloxacin has an aqueous solubility 3.5 times higher when cocrystallized with saccharin than in its pristine state, and an inverted pH-dependency compared to NOR alone (2 times higher in 6.1, slightly increase in pH 3.0, and a decrease of 0.7 times in 8.5 buffer solution). Furthermore, the solvate–cocrystal has a water solubility 2.3 times higher than NOR and the same solubility in 6.1 buffer solution than the cocrystal (2 times higher than NOR alone).

Simultaneous electrochemical sensing of dihydroxy benzene isomers at cost-effective allura red polymeric film modified glassy carbon electrode

Abstract: A simple and simultaneous electrochemical sensing platform was fabricated by electropolymerization of allura red on glassy carbon electrode (GCE) for the interference-free detection of dihydroxy benzene isomers. The modified working electrode was characterized by electrochemical and field emission scanning electron microscopy methods. The modified electrode showed excellent electrocatalytic activity for the electrooxidation of catechol (CC) and hydroquinone (HQ) at physiological pH of 7.4 by cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques. The effective split in the overlapped oxidation signal of CC and HQ was achieved in a binary mixture with peak to peak separation of 0.102 V and 0.103 V by CV and DPV techniques. The electrode kinetics was found to be adsorption-controlled. The oxidation potential directly depends on the pH of the buffer solution, and it witnessed the transfer of equal number of protons and electrons in the redox phenomenon. The limit of detection (LOD) for CC and HQ was calculated to be 0.126 μM and 0.132 μM in the linear range of 0 to 80.0 μM and 0 to 110.0 μM, respectively, by ultra-sensitive DPV technique. The practical applicability of the proposed sensor was evaluated for tap water sample analysis, and good recovery rates were observed. Electrocatalytic interaction of ALR/GCE with dihydroxy benzene isomers.

AFM study of changes in properties of horseradish peroxidase after incubation of its solution near a pyramidal structure.

Abstract: In our present paper, the influence of a pyramidal structure on physicochemical properties of a protein in buffer solution has been studied. The pyramidal structure employed herein was similar to those produced industrially for anechoic chambers. Pyramidal structures are also used as elements of biosensors. Herein, horseradish peroxidase (HRP) enzyme was used as a model protein. HRP macromolecules were adsorbed from their solution onto an atomically smooth mica substrate, and then visualized by atomic force microscopy (AFM). In parallel, the enzymatic activity of HRP was estimated by conventional spectrophotometry. Additionally, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) has been employed in order to find out whether or not the protein secondary structure changes after the incubation of its solution either near the apex of a pyramid or in the center of its base. Using AFM, we have demonstrated that the incubation of the protein solution either in the vicinity of the pyramid’s apex or in the center of its base influences the physicochemical properties of the protein macromolecules. Namely, the incubation of the HRP solution in the vicinity of the top of the pyramidal structure has been shown to lead to an increase in the efficiency of the HRP adsorption onto mica. Moreover, after the incubation of the HRP solution either near the top of the pyramid or in the center of its base, the HRP macromolecules adsorb onto the mica surface predominantly in monomeric form. At that, the enzymatic activity of HRP does not change. The results of our present study are useful to be taken into account in the development of novel biosensor devices (including those for the diagnosis of cancer in humans), in which pyramidal structures are employed as sensor, noise suppression or construction elements.

Stabilization of DNA by sodium and magnesium ions during the synthesis of DNA-bridged gold nanoparticles.

Abstract: Nanostructures synthesized using DNA-conjugated gold nanoparticles have a wide range of applications in the field of biosensorics. The stability of the DNA duplex plays a critical role as it determines the final geometry of these nanostructures. The main way to control DNA stability is to maintain a high ionic strength of the buffer solution; at the same time, high salt concentrations lead to an aggregation of nanoparticles. In this study, by means of the instrumentality of DNA-bridged seeds using tris(hydroxymethyl)aminomethane as a soft reducing agent the dumbbell-like gold nanoparticles up to 35 nm were synthesized with a high concentration of sodium ions of up to 100 mM and magnesium ions up to 1 mM. We also examined at the atomic level the details of the effect of the gold nanoparticle surface, as well as Na+ and Mg2+ ions, on the stability of nucleotide pairs located in close proximity to the grafting site.

Modeling Microtubule Counterion Distributions and Conductivity Using the Poisson-Boltzmann Equation.

Abstract: Microtubules are highly negatively charged proteins which have been shown to behave as bio-nanowires capable of conducting ionic currents The electrical characteristics of microtubules are highly complicated and have been the subject of previous work; however, the impact of the ionic concentration of the buffer solution on microtubule electrical properties has often been overlooked In this work we use the non-linear Poisson Boltzmann equation, modified to account for a variable permittivity and a Stern Layer, to calculate counterion concentration profiles as a function of the ionic concentration of the buffer We find that for low-concentration buffers ([KCl] from 10 μM to 10 mM) the counterion concentration is largely independent of the buffer's ionic concentration, but for physiological-concentration buffers ([KCl] from 100 to 500 mM) the counterion concentration varies dramatically with changes in the buffer's ionic concentration We then calculate the conductivity of microtubule-counterion complexes, which are found to be more conductive than the buffer when the buffer's ionic concentrations is less than ≈100 mM and less conductive otherwise These results demonstrate the importance of accounting for the ionic concentration of the buffer when analyzing microtubule electrical properties both under laboratory and physiological conditions We conclude by calculating the basic electrical parameters of microtubules over a range of ionic buffer concentrations applicable to nanodevice and medical applications

Selective Extraction of Sinapic Acid Derivatives from Mustard Seed Meal by Acting on pH: Toward a High Antioxidant Activity Rich Extract.

Abstract: The aim of this paper is to study the effect of the pH on the extraction of sinapic acid and its derivatives from mustard seed meal. Solutions of acidic pH (pH 2), basic pH (pH 12) and distilled water (uncontrolled pH ~ 4.5) were tested at different percentages of ethanol. The maximum extraction yield for sinapic acid (13.22 µmol/g of dry matter (DM)) was obtained with a buffered aqueous solution at pH 12. For ethyl sinapate, the maximum extraction yield reached 9.81 µmol/g DM with 70% ethanol/buffered aqueous solution at pH 12. The maximum extraction yield of sinapine (15.73 µmol/g DM) was achieved with 70% ethanol/buffered aqueous solution at pH 2. The antioxidant activity of each extract was assessed by DPPH assay; the results indicated that the extracts obtained at pH 12 and at low ethanol percentages (<50%) exhibit a higher antioxidant activity than extracts obtained at acidic conditions. Maximum antioxidant activity was reached at pH 12 with buffer solution (11.37 mg of Trolox Equivalent/g DM), which confirms that sinapic acid-rich fractions exhibit a higher antioxidant activity. Thus, to obtain rich antioxidant extracts, it is suggested to promote the presence of sinapic acid in the extracts.

Synthesis and Characterization of a (-)-Epicatechin and Barbituric Acid Cocrystal: Single-Crystal X-ray Diffraction and Vibrational Spectroscopic Studies.

Abstract: The paper presents the contribution of the cocrystallization method in the physicochemical modification of catechins that exhibit low oral bioavailability. This was done to obtain cocrystals for two naturally occurring polyphenolic diastereoisomers (+)-catechin and (-)-epicatechin with commonly used coformers. Due to distinct crystallization behavior, only the (-)-epicatechin cocrystal with barbituric acid in a 1:1 stoichiometry was obtained. The cocrystal of (-)-epicatechin (EC) with barbituric acid (BTA) was prepared by the slow solvent-evaporation technique. The structure and intermolecular interactions were determined by X-ray crystallographic techniques. The analysis of packing and interactions in the crystal lattice revealed that molecules in the target cocrystal were packed into tapes, formed by the O-H···O type contacts between the (-)-epicatechin and coformer molecules. The EC molecules interact with the carboxyl group in the BTA coformer mainly by -OH groups from the benzene ring A. The cocrystalline phase constituents were also investigated in terms of Hirshfeld surfaces. The application of Raman spectroscopy confirmed the involvement of the C=O group in the formation of hydrogen bonds between the (-)-epicatechin and barbituric acid molecules. Additionally, the solubility studies of pure EC and the EC-BTA cocrystal exhibited minor enhancement of EC solubility in the buffer solution, and pH measurements confirmed a stable level of solubility for EC and its cocrystal.

Assembly of a Hexameric Cluster of Polyoxomolybdotriphosphonate Builts from [Zn(H2O){TeMo6O21}{N(CH2PO3)3}]6- Subunits and Its Optical and Catalytic Properties.

Abstract: The crown-shaped organotriphosphonate-modified 36-molybdenum cluster (NH4)18Na7H11[Zn(H2O)TeMo6O21{N(CH2PO3)3}]6·23H2O (1) has been synthesized, which is the largest zinc-containing organophosphonate-based polyoxometalate to date. Compound 1 was prepared in buffer solution (pH 5.5) with heptamolybdate and amino trimethylene phosphonic acid (ATMP) as the organic ligand. The polyanion constructed from a hexmeric assembly of [Zn(H2O){TeMo6O21}{N(CH2PO3)3}]6- subunits has been fully investigated by a few characterization methods. In this work, we discovered that 1 exhibited reversible photochromism and it changed from white to reddish brown upon UV irradiation. In addition, compound 1, as a catalyst, can oxidize sulfides to sulfoxides, showing a high yield/conversion and a good selectivity.

Poly(vinyl alcohol)/poly(hydroxypropyl methacrylate- co -methacrylic acid) as pH-sensitive semi-IPN hydrogels for oral insulin delivery: preparation and characterization

Abstract: A series of pH-sensitive semi-interpenetrating polymer network (semi-IPN) hydrogels poly(vinyl alcohol)/poly(hydroxypropyl methacrylate-co-methacrylic acid) (PVA/P(HPMA-co-MAA)) were synthesized by free-radical polymerization of HPMA and MAA in the presence of PVA. The physicochemical property of the obtained hydrogels was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analyses and scanning electron microscopy (SEM) measurements. The SEM photograph revealed the network formation with uniform pore distribution. The swelling behavior of each hydrogel in buffer solution showed a simultaneous sensitivity to pH and ionic strength: the swelling ratio of all hydrogels was higher in neutral environment than in acidic medium; besides, equilibrium swelling ratio of the hydrogels decreases as the ionic strength increases. Insulin was loaded into the PVA/P(HPMA-co-MAA) semi-IPN hydrogel. The in vitro insulin release experiment was carried out in buffer solutions at pHs 1.2 and 6.8. Results showed that the release of entrapped insulin was inhibited at pH 1.2 but obviously increased at pH 6.8. Cell viability revealed that the hydrogels were biocompatible. After oral administration of insulin-loaded hydrogel to streptozotocin-induced diabetic rats at 75 IU/kg, a sustained reduction in blood glucose level was observed. Therefore, the semi-IPN PVA/P(HPMA-co-MAA) hydrogels are potential vehicles for oral delivery of protein drugs.

Synthesis of carbon dots for Al3+ sensing in water by fluorescence assay.

Abstract: Fifty-four Eucommia ulmoides leaves were subjected to a hydrothermal technique to synthesize carbon dots (CDs) of 355 ± 145 nm size The nanomaterial possessed excellent stability and strong fluorescence emission (φf 423%) In a neutral buffer solution, the fluorescence signals of CDs solution were enhanced by aluminium ion without interference from other ions Degree of enhancement correlated linearly with the Al3+ content in the range 001-25 mM Response of this method was fast and sensitive (detection limit was 23 nM) The CDs performed successfully as a sensitive sensor for trace Al3+ determination in water samples, and satisfactory results were obtained

A New Coumarin-Acridone Compound as a Fluorescence Probe for Fe3+ and Its Application in Living Cells and Zebrafish

Abstract: A new coumarin-acridone fluorescent probe S was designed and synthesized, and the structure was confirmed with 1H/13C NMR spectrometry, single-crystal X-ray diffraction, and high-resolution mass spectrometry. This probe has high sensitivity and selectivity for Fe3+ over other testing metal ions at 420 or 436 nm in acetonitrile-MOPS (3-Morpholinopropanesulfonic Acid) buffer solution (20.0 μM, pH = 6.9, 8:2 (v/v)). Under physiological conditions, the probe displayed satisfying time stability with a detection limit of 1.77 µM. In addition, probe S was successfully used to detect intracellular iron changes through a fluorescence-off mode, and the imaging results of cells and zebrafish confirmed their low cytotoxicity and satisfactory cell membrane permeability, as well as their potential biological applications.

A novel voltammetric method for the sensitive and selective determination of carbonate or bicarbonate ions by an azomethine-H probe.

Abstract: Our study involved a simple, sensitive voltammetric method of determining either carbonate or bicarbonate ions independently with azomethine-H and a disposable pencil graphite electrode. The reduction of azomethine-H–carbonate complexes at approximately −930 mV formed in acetic acid–acetate buffer solution (pH: 4.25) was evaluated as a response. Among the results, the limits of detection and analytical ranges for carbonate ions were 3.7 μg L−1 and 9.9–700.0 μg L−1 and for bicarbonate ions were 9.0 μg L−1 and 35.0–700.0 μg L−1, and the relative standard deviations for carbonate and bicarbonate ions ranged from 1.33% and 6.93% at different concentrations. After the proposed method was applied to water, sparkling water, seawater and baking powder samples, the results were statistically evaluated and compared with those obtained from the potentiometric auto-titration system. Last, the complex stoichiometry of both carbonate and bicarbonate ions was comprehensively investigated with fluorescence and 1H-NMR spectroscopy.