pH-triggered PMAA-b-HTPB-b-PMAA copolymer micelles: physicochemical characterization and camptothecin release

pH-sensitive poly(methacrylic acid)-block-hydroxyl-terminated polybutadiene-block-poly(methacrylic acid) block copolymers were synthesized by atom transfer radical polymerization of t-butyl methacrylate and follow-up acidolysis. The copolymers can spontaneously assemble into stable and nearly spherical micelle aggregates in aqueous solution, with hydrodynamic diameters (D _h ) from 51 to 92 nm and critical micelle concentration of 3.90–7.76 mg L^?1. Zeta potentials were found to be increased with increasing (monomer)/(initiator) molar ratios. A pH-dependent phase behavior is produced at approximately 5.4–5.6, as determined by D _h and I ₃₃₅/I ₃₃₂ fluorescence intensity ratios. The in vitro camptothecin (CPT) release was compositional and pH dependent, and the cumulative CPT release below pH 7.2 was higher than that in pH 7.4. They could inhibit the premature burst CPT release. The copolymer micelles were low in cytotoxicity even at a micellar concentration of 800 mg L^?1, and therefore they may be used as potential drug-delivery carriers.

A novel synthesis of (3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9-(4-vinylbenzyl)-9H-carbazole), alternating polymer formation, characterization, and capacitance measurements

In this work, (3,6-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-9-(4-vinylbenzyl)-9H-carbazole) (EDOTVBCz) comonomer was chemically synthesized and characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance, and carbon nuclear magnetic resonance spectroscopy. EDOTVBCz was electrocoated on glassy carbon electrode (GCE) in various initial molar concentrations ([EDOTVBCz]₀?=?1.0, 1.5, 2.0, and 3.0) in 0.1 M lithium perchlorate (LiClO₄)/acetonitrile (CH₃CN). P(EDOTVBCz)/GCE was characterized by cyclic voltammetry, FTIR reflectance-attenuated total reflection spectroscopy, scanning electron microscopy–energy dispersive X-ray analysis, atomic force microscopy, and electrochemical impedance spectroscopy (EIS). EIS was used to determine the capacitive behaviors of modified GCE via Nyquist, Bode magnitude, Bode phase, and admittance plots. The highest low-frequency capacitance value was obtained as C _LF?=?～2.35 mF cm^?2 for [EDOTVBCz]₀?=?3.0 mM. Double-layer capacitance of the polymer/electrolyte system was calculated as C _dl?=?～2.78 mF cm^?2 for [EDOTVBCz]₀?=?1.0 and 3.0 mM. The maximum phase angle was obtained as θ?=?～76.7^o for [EDOTVBCz]₀?=?1.0, 1.5, 2.0, and 3.0 mM at the frequency of 20.6 Hz. AC impedance spectra of P(EDOTVBCz)/LiClO₄/CH₃CN was obtained by performing electrical equivalent circuit model of R(Q(R(CR))) with linear Kramers–Kronig test.

Detection of trace nitrite in waters using a QDs-based chemiluminescence analysis system

In the present work, a novel flow-injection chemiluminescence method based on CdTe quantum dots (QDs) was developed for the determination of nitrite. Weak chemiluminescence (CL) signals were observed from a CdTe QDs–H₂O₂ system under basic conditions. The addition of a trace amount of hemoglobin (Hb) caused the CL from the CdTe QDs–H₂O₂ system to increase substantially. In the presence of nitrite, the ferrous Hb reacted with the nitrate to form ferric Hb and NO. The NO then bound to ferrous Hb to generate iron nitrosyl Hb. As a result, the CL signal from the CdTe QDs–H₂O₂–Hb system was quenched. Thus, a flow-injection CL analytical system for the determination of trace nitrite was established. Under optimum conditions, there was a good linear relationship between CL intensity and the concentration of nitrite in the range 1.0?×?10^?9 to 8.0?×?10^?7 mol L^?1 (R ²?=?0.9957). The limit of detection for nitrite using this system was 3.0?×?10^?10 mol L^?1 (S/N?=?3). This method was successfully applied to detect nitrite in water samples.

Magnetic titanium oxide nanoparticles for hemimicelle extraction and HPLC determination of organophosphorus pesticides in environmental water

We report on a method for the extraction of organophosphorus pesticides (OPPs) from water samples using mixed hemimicelles and magnetic titanium dioxide nanoparticles (Fe₃O₄@TiO₂) modified by cetyltrimethylammonium. Fe₃O₄@TiO₂ nanoparticles were synthesized by a hydrothermal process and then characterized by scanning electron microscopy and Fourier transform IR spectrometry. The effects of the quantity of surfactant, extraction time, desorption solvent, pH value, extraction volume and reuse of the sorbent were optimized with respect to the extraction of OPPs including chlorpyrifos, dimethoate, and trichlorfon. The extraction method was applied to analyze OPPs in environmental water using HPLC along with UV detection. The method has a wide linear range (100–15,000 ng L^?1), good linearity (r?>?0.999), and low detection limits (26–30 ng L^?1). The enrichment factor is ~1,000. The recoveries (at spiked levels of 100, 1,000 and 10,000 ng L^?1) are in the range of 88.5–96.7 %, and the relative standard deviations range from 2.4 % to 8.7 %.

Glucose biosensor based on a platinum electrode modified with rhodium nanoparticles and with glucose oxidase immobilized on gold nanoparticles

We have developed an enzymatic glucose biosensor that is based on a flat platinum electrode which was covered with electrophoretically deposited rhodium (Rh) nanoparticles and then sintered to form a large surface area. The biosensor was obtained by depositing glucose oxidase (GOx), Nafion, and gold nanoparticles (AuNPs) on the Rh electrode. The electrical potential and the fractions of Nafion and GOx were optimized. The resulting biosensor has a very high sensitivity (68.1 μA mM^?1 cm^?2) and good linearity in the range from 0.05 to 15 mM (r?=?0.989). The limit of detection is as low as 0.03 mM (at an SNR of 3). The glucose biosensor also is quite selective and is not interfered by electroactive substances including ascorbic acid, uric acid and acetaminophen. The lifespan is up to 90 days. It was applied to the determination of glucose in blood serum, and the results compare very well with those obtained with a clinical analyzer.

Preconcentration of trace cadmium ion using magnetic graphene nanoparticles as an efficient adsorbent

Graphene-based magnetic nanoparticles (G-Fe₃O₄) were prepared and used as an effective adsorbent for the solid-phase extraction of trace quantities of cadmium from water and vegetable samples. The method avoids some of the time-consuming steps associated with traditional solid phase extraction. The excellent sorption property of the G-Fe₃O₄ system is attributed to π - π stacking interaction and hydrophobic interactions between graphene and the Cd-PAN complex. The effects of pH, the amount of G–Fe₃O₄, extraction time, type and volume of eluent, desorption time and interfering ions on the extraction efficiency were optimized. The preconcentration factor is 200. Cd(II) was then quantified by flame atomic absorption spectrometry with a detection limit of 0.32 ng mL^?1. The relative standard deviation (at 50 ng mL^?1; for n?=?10) is 2.45 %. The method has a linear analytical range from 1.1 to 150 ng mL^?1, and the recoveries in case of real samples are in the range between 93.1 % and 102.3 %.

Determination of phthalate esters in edible oils by use of QuEChERS coupled with ionic-liquid-based dispersive liquid–liquid microextraction before high-performance liquid chromatography

A selective and low organic-solvent-consuming method of sample preparation combined with high-performance liquid chromatography with diode-array detection is introduced for analysis of phthalic acid esters in edible oils. Sample treatment involves initial liquid–liquid partitioning with acetonitrile, then QuEChERS cleanup by dispersive solid-phase extraction with primary secondary amine as sorbent. Preconcentration of the analytes is performed by ionic-liquid-based dispersive liquid–liquid microextraction, with the cleaned-up extract as disperser solvent and 1-hexyl-3-methylimidazolium hexafluorophosphate as extraction solvent. Under the optimized conditions, correlation coefficients (r) were 0.998–0.999 and standard errors (S _y/x ) were 2.67–3.37?×?10³ for calibration curves in the range 50–1000 ng g^?1. Detection limits, at a signal-to-noise ratio of 3, ranged from 6 to 9 ng g^?1. Intra-day and inter-day repeatability, expressed as relative standard deviation, were in the ranges 1.0–6.9 % and 2.4–9.4 %, respectively. Recovery varied between 84 % and 106 %. The developed method was successfully used for analysis of the analytes in 28 edible oils. The dibutyl phthalate content of four of the 28 samples (14 %) exceeded the specific migration limit established by domestic and international regulations.

Voltammetric sensing of thallium at a carbon paste electrode modified with a crown ether

We describe a new method for differential-pulse anodic stripping voltammetric determination of thallium(I) using a carbon paste electrode modified with dicyclohexyl-18-crown-6. The effect of supporting electrolyte (type and pH), accumulation and reduction potential, and of time and amount of modifier were investigated by differential pulse anodic stripping voltammetry. A method was then worked out for the determination of thallium at low levels. Under optimized conditions, the response to Tl(I) is linear in the range from 3.0 to 250 ng mL^?1. The detection limit is 0.86 ng mL^?1. The sensor displays good repeatability (with a relative standard deviation of ±2.70 % for n?=?7) and was applied to the determination of Tl(I) in water, hair samples, and certified reference materials.

Determination of formaldehyde based on the enhancement of the chemiluminescence produced by CdTe quantum dots and hydrogen peroxide

Water-soluble cadmium telluride quantum dots (CdTe QDs) capped with glutathione (GSH) display chemiluminescence (CL) emission on reaction with hydrogen peroxide (H₂O₂) in strongly alkaline medium. It is found that the CL is strongly enhanced on addition of formaldehyde in aqueous solution. A flow injection system was developed, and it is shown that there is good linearity between CL intensity and the concentration of formaldehyde in the 0.06–3.0 μg L^?1 range. The limit of detection is as low as 10 ng L^?1. The method was successfully applied to the determination of formaldehyde in indoor air after adsorption into an aqueous phase. The recoveries for the real samples range from 97 % to 102.5 %, and the relative standard deviation is <3.8 % for intra- and inter-assay precision.

Application of response function methodology for the simultaneous determination of potential fragrance allergens and preservatives in personal care products using micellar electrokinetic chromatography

A micellar electrokinetic chromatography method was developed for determination of 15 suspected fragrance allergens and preservatives. The target compounds are widely used as ingredients in many personal care products, and all of them are included in the European Regulation concerning cosmetic products. The method was optimized by using a central composite experimental design and response surface methodology. A modified chromatographic response function was defined to weigh the terms in the response function adequately. After optimization of experimental conditions, a background electrolyte of 100 mM sodium dodecyl sulphate and 24 mM sodium tetraborate and pH 9.0 was selected for the separation of the analytes. The developed methodology was evaluated in terms of linearity, limits of detection and quantification, precision and accuracy, showing appropriate values (i.e., R ²?=?≥0.99 and accuracy of 89–115 %). Finally, applicability of the micellar electrokinetic chromatography method was assessed by successfully quantifying fragrance allergens and preservatives in commercial personal care products. The most commonly found analyte was linalool (48.3 % of samples) followed by benzoic acid (37.6 %). All samples contained at least one of the target compounds, thus confirming the ubiquity of fragrance allergens and preservatives in personal care products.

An enzymatic glucose biosensor based on a glassy carbon electrode modified with manganese dioxide nanowires

A glassy carbon electrode was modified with β-manganese dioxide (β-MnO₂), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO₂ nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO₂ nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO₂ acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM^?1?·?cm^?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO₂ nanowires.

Electrochemical investigation of the interaction between lysozyme-shelled microbubbles and vitamin C

We report loading of vitamin C (ascorbic acid) on to lysozyme-shelled microbubbles. The interaction between lysozyme-shelled microbubbles and vitamin C was studied by use of cyclic and differential pulse voltammetry, zeta potential measurements, and scanning electron microscopy. The effect of microbubbles on electrochemical measurement of ascorbic acid was evaluated. The linear range for ascorbic acid obtained for differential pulse measurement in the presence of 1 mg mL^?1 microbubbles was 1–50 μmol L^?1 (y?=?0.067x?+?0.130, r ²?=?0.995), with a detection limit of 0.5 μmol L^?1. The experimental conditions, i.e., pH and ionic strength, were optimized to improve the interaction between ascorbic acid and lysozyme-shelled microbubbles. The results were satisfactory when the interaction was performed for 1 h in aqueous solution at pH 6. The amount of vitamin C loaded on the microbubbles (90 % of the analyte added, RSD _inter-expt. = 3 %, n?=?6) and the stability of microbubbles–ascorbic acid complex (until 72 h at 25 °C) were also evaluated by use of differential pulse voltammetry and zeta potential measurements.

Synergistic extraction of some divalent metal cations into nitrobenzene by using strontium dicarbollylcobaltate and electroneutral macrocyclic lactam receptor

From extraction experiments and $ \gamma $ -activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + 1·Sr²⁺(nb) $ \Leftrightarrow $ 1·M²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Cu²⁺, Zn²⁺, Cd²⁺, $ {\hbox{UO}}_{2}^{2 + } $ , Mn²⁺, Co²⁺, Ni²⁺; 1 = macrocyclic lactam receptor–see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1·M²⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: Mg²⁺ < Co²⁺ < Cu²⁺, Mn²⁺, Ni²⁺ < Cd²⁺ < Ca²⁺ < Ba²⁺, Zn²⁺ < Pb²⁺ <  $ {\hbox{UO}}_{2}^{2 + } $ .

Water-soluble homo-oligonucleotide stabilized fluorescent silver nanoclusters as fluorescent probes for mercury ion

Water–soluble fluorescent silver nanoclusters (Ag NCs) were prepared with the assistance of commercially available polyinosinic acid (PI) or polycytidylic acid (PC). The fluorescence of the Ag NCs is effectively quenched by trace mercury(II) ions, which can be applied for their detection. The response of the Ag NCs prepared with PI to Hg(II) ion is linear in the Hg(II) concentration range from 0.05 to 1.0 μM (R²?=?0.9873), and from 0.5 to 10 μM of Hg(II) (R²?=?0.9971) for Ag NCs prepared with PC. The detection limits are 3.0 nM and 9.0 nM (at an S/N of 3), respectively. The method is simple, sensitive and fairly selective.

High-resolution monolithic columns—a new tool for effective and quick separation

This work describes a comparison of three types of commercial high-performance liquid chromatography silica monolithic columns with different inner diameters and generations of monolithic sorbent: a “classic” monolithic column, the first generation (Onyx? monolithic C₁₈, 100 mm?×?4.6 mm, Phenomenex); a “narrow” monolithic column for fast separation at lower flow rates (Chromolith® Performance RP-18e, 100 mm?×?3 mm, Merck); and a recently introduced “high-resolution” monolithic column, the next generation (Chromolith® HighResolution RP-18e, 100 mm?×?4.6 mm, Merck). Separation efficiency (number of theoretical plates, height equivalent to a theoretical plate and van Deemter curves), working pressure, the symmetry factor and resolution were critical aspects of the comparison in the case of the separation of ascorbic acid, paracetamol and caffeine. The separations were performed under isocratic conditions with a mobile phase consisting of 10:90 (v/v) acetonitrile–phosphoric acid (pH 2.80). Detailed comparison of the newest-generation monolithic column (Chromolith® HighResolution) with the previously introduced monolithic sorbents was performed and proved the advantages of the Chromolith® HighResolution column.

Cetyltrimethylammonium-coated magnetic nanoparticles for the extraction of bromate,followed by its spectrophotometric determination

We report on a combination of magnetic solid-phase extraction and spectrophotometric determination of bromate. Cetyltrimethylammonium ion was adsorbed on the surface of phenyl-functionalized silica-coated Fe₃O₄ nanoparticles (Ph-SiO₂@Fe₃O₄), and these materials served as the sorbent. The effects of surfactant and amount of sorbent, the composition of the desorption solution, the extraction time and temperature were optimized. Under optimized conditions, an enrichment factor of 12 was achieved, and the relative standard deviation is 2.9 % (for n?=?5). The calibration plot covers the 1–50 ng mL^?1 range with reasonable linearity (r ²?>?0.998); and the limit of detection is 0.5 ng mL^?1. The method is not interfered by ionic compounds commonly found in environmental water samples. It was successfully applied to the determination of bromate in spiked water samples.

Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO₂ nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM^?1 cm^?2, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication.

Measuring Positive Cooperativity Using the Direct ESI-MS Assay. Cholera Toxin B Subunit Homopentamer Binding to GM1 Pentasaccharide

Direct electrospray ionization mass spectrometry (ESI-MS) assay was used to investigate the stepwise binding of the GM1 pentasaccharide β-D-Galp-(1→3)-β-D-GalpNAc-(1→4)[α-D-Neu5Ac-(2→3)]-β-D-Galp-(1→4)-β-D-Glcp (GM1os) to the cholera toxin B subunit homopentamer (CTB₅) and to establish conclusively whether GM1os binding is cooperative. Apparent association constants were measured for the stepwise addition of one to five GM1os to CTB₅ at pH 6.9 and 22 °C. The intrinsic association constant, which was established from the apparent association constant for the addition of a single GM1os to CTB₅, was found to be (3.2 ± 0.2) × 10⁶ M^–1. This is in reasonable agreement with the reported value of (6.4 ± 0.3) × 10⁶ M^–1, which was measured at pH 7.4 and 25 °C using isothermal titration calorimetry (ITC). Analysis of the apparent association constants provides direct and unambiguous evidence that GM1os binding exhibits small positive cooperativity. Binding was found to be sensitive to the number of ligand-bound nearest neighbor subunits, with the affinities enhanced by a factor of 1.7 and 2.9 when binding occurs next to one or two ligand-bound subunits, respectively. These findings, which provide quantitative support for the binding model proposed by Homans and coworkers [14], highlight the unique strengths of the direct ESI-MS assay for measuring cooperative ligand binding.

Optical determination of glucose and hydrogen peroxide using a nanocomposite prepared from glucose oxidase and magnetite nanoparticles immobilized on graphene oxide

Fe₃O₄ nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe₃O₄/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe₃O₄/GO nanoparticles cause the generation of H₂O₂ which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H₂O₂ ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe₃O₄/GO nanoparticles are reusable.

In-situ decorated gold nanoparticles on polyaniline with enhanced electrocatalysis toward dopamine

Gold nanoparticles were in-situ decorated on top of a polyaniline film (GNPs–PANI) via the direct electroreduction of the adsorbed AuCl ₄ ^- ions on a glassy carbon electrode that previously was coated with PANI by electropolymerization. The GNPs–PANI composite and the performance of the resultant sensors were investigated in some detail. The sensor was applied to the oxidation of dopamine (DA) with improved catalytic activity. Its catalytic current showed wide linear response toward dopamine ranging from 3 to 115 μM, with a low detection limit of 0.8 μM (S/N=3). In addition, the sensor exhibits easy-operation, fast response to dopamine, as well as excellent reproducibility and stability.