A sensor based on incorporating Ni2+ into ZnO nanoparticles-multi wall carbon nanotubes-poly methyl metacrylat nanocomposite film modified carbon paste electrode for determination of carbohydrates

The ZnO nanoparticles (ZnONPs) were synthesized with gelatin as stabilizer via the sol-gel method and were characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). An electrochemical sensor based on ZnO nanoparticles-multi wall carbon nanotubes-poly methyl metacrylat (ZnONPs-MWCNT-PMMA) composite film was developed by incorporating Ni²⁺ into the ZnONPs-MWCNT-PMMA film modified carbon paste electrode (Ni²⁺/ZnONPs-MWCNT-PMMA/CPE). The electrochemical activity of Ni²⁺/ZnONPs-MWCNT-PMMA/CPE was illustrated in 0.10 M NaOH using cyclic voltammetry. The Ni²⁺/ZnONPs-MWCNT-PMMA/CPE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple. Ni²⁺/ZnONPs-MWCNT-PMMA/CPE also show good electrocatalytic activity toward the oxidation of carbohydrates (glucose, fructose and sorbitol). The Ni²⁺/ZnONPs-MWCNT-PMMA/CPE gives a good linear range with a detection limit of 8, 6, and 9 μM towards the determination of glucose, fructose and sorbitol, respectively by amperometry. Furthermore, the modified sensor was successfully applied to the sensitive determination of carbohydrates in real samples.     

Thermal decomposition of polymethylmethacrylate synthesized with anionic catalysts

TG and DTA data are used to show that the thermal decomposition of polymethylmethacrylate (PMMA) synthesized with anionic catalysts depends on the nature of the catalyst. It is found that the thermal stability of PMMA obtained by using anionic amide catalysts is higher than that of radical PMMA and of PMMA obtained with other anionic catalysts, and depends on the temperature of polymerization and on the molecular weight of the polymer.     

Miscibility and crystallization behaviors of stereocomplex-type poly(l- and d-lactide)/poly(methyl methacrylate) blends

Stereocomplex-poly(l- and d-lactide) (sc-PLA) and poly(methyl methacrylate) (PMMA) blends were prepared by solution blending at PMMA loadings from 20 to 80 mass%. The miscibility and crystallization behaviors of the blends have been studied in detail by differential scanning calorimeter. The single-glass transition temperatures (T _g) of the blends demonstrated that the obtained system was miscible in the amorphous state. It was observed that the crystallization peak temperature of sc-PLA/PMMA blends was marginally lower than that of neat sc-PLA at various cooling rates, indicating the dilution effect of PMMA on the sc-PLA component to restrain the overall crystallization process. In the study of isothermal crystallization kinetics, the reciprocal value of crystallization peak time ( \( t_{\text{p}}^{ - 1} \) ) decreased with increasing PMMA content, indicating that the addition of non-crystalline PMMA inhibited the isothermal crystallization of sc-PLA at an identical crystallization temperature (T _c). Moreover, the negative value of Flory–Huggins interaction parameter (χ ₁₂ = ?0.16) of the blend further indicated that sc-PLA and PMMA formed miscible blends.     

Carbon nanotubes induced poly(vinylidene fluoride) crystallization from a miscible poly(vinylidene fluoride)/poly(methyl methacrylate) blend

Different contents of carbon nanotubes (CNTs) were introduced into a miscible poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend. The interfacial affinity between CNTs and components of the blend was evaluated by calculating the interfacial tension. The dispersion and microstructure of CNTs in the nanocomposites were investigated through scanning electron microscope and rheological measurement. The effect of CNTs on the crystallization of PVDF was comparatively investigated through nonisothermal and isothermal crystallization processes. The results showed that CNTs exhibited stronger interfacial affinity to PMMA. Homogeneous dispersion of CNTs in the nanocomposites was achieved. Largely enhanced crystallization temperature and increased crystallinity of PVDF were obtained by adding CNTs during the nonisothermal crystallization process. The results obtained from the isothermal crystallization process proved that CNTs induced the concentration fluctuation in the sample, which resulted in the formation of spherulites with different types, i.e., the banded spherulites and compact spherulites. Furthermore, both the crystallization temperature and the content of CNTs exhibited great influence on the crystalline morphology of PVDF.     

Graft copolymers via combination of cationic polymerization and atom transfer radical polymerization and their phase separation into spherical/worm-like nanostructures

Poly(p-chloromethyl styrene)-graft-poly(methyl methacrylate) (PCMS-g-PMMA) and poly(p-chloromethyl styrene)-graft-poly(benzyl methacrylate) (PCMS-g-PBzMA) graft copolymers with asymmetric branches are synthesized via the combination of cationic polymerization and atom transfer radical polymerization (ATRP). The process involves first, the preparation of poly(p-chloromethyl styrene) (PCMS-CH₂Cl) macroinitiator without any cross-linking or side reactions through pendant benzyl chloride (?CH₂Cl) functionality by cationic polymerization using a simple FeCl₃-based initiating system at 25 °C. The as-synthesized PCMS-CH₂Cl, without any transformation, is then used as the macroinitiator to graft PMMA and PBzMA branches by ATRP to produce PCMS-g-PMMA and PCMS-g-PBzMA graft copolymers of varying compositions with controlled molecular weight and moderately narrow polydispersities (M _w/M _n?≤?1.32). The resulting PCMS₂₁ -g-PMMA₂₃₂ graft copolymer in thin film form phase separates into spherical morphology with an average diameter of 170?±?72 nm. Whereas the PCMS₂₁ -g-PBzMA₁₅₆ graft copolymer gives worm-like nanostructures with an average length of 94 nm and width of 31 nm due to phase separation as visualized through atomic force microscopy. On the other hand, the phase-separated morphology is not very well-defined for other graft copolymers (PCMS₁₁₃ -g-PMMA₂₂₇ and PCMS₁₁₃ -g-PBzMA₁₅₄) thin films containing longer PCMS chains. This approach represents a rapid and convenient route to prepare unique spherical/worm-like polymer nanostructures. Figure

Well-defined poly(p-chloromethyl styrene)-graft-poly(methyl methacrylate) (PCMS-g-PMMA) and poly(p-chloromethyl styrene)-graft-poly(benzyl methacrylate) (PCMS-g-PBzMA) graft copolymers with asymmetric branches are synthesized by the combination of living cationic polymerization and atom transfer radical polymerization (ATRP). The resulting PCMS₂₁ -g-PMMA₂₃₂ and PCMS₂₁ -g-PBzMA₁₅₆ graft copolymers phase separate into nanostructured spherical and worm-like morphologies, respectively, in thin film form. The phase-separated morphology is not very well-defined for graft copolymers (PCMS₁₁₃ -g-PMMA₂₂₇ and PCMS₁₁₃ -g-PBzMA₁₅₄) thin films containing longer PCMS chains.     

Reverse atom transfer radical polymerization of methyl methacrylate in the presence of Azo-functionalized carbon nanotubes: a grafting from approach

After oxidation of carbon nanotubes (CNT), its carboxyl groups were subsequently converted to acyl chloride and hydroxyl functionalities. Subsequently, 4,4′-azobis (4-cyanopentanoic acid) (ACPA) was attached to the hydroxyl groups of nanotubes by an esterification reaction to yield azo initiator-anchored nanotubes (CNTAzo). Then, grafting from reverse atom transfer radical polymerization of methyl methacrylate in the presence of CNTAzo in different weight percents was carried out. Appearance of N_1s band in the spectrum of CNTAzo originates from the covalent attachment of ACPA on CNT. Successful functionalization of CNT with EG, ACPA, and PMMA was also proved by FTIR. SEC results show that molecular weight and PDI values of the attached chains are higher. XRD and Raman spectroscopy were used to study the structural characteristics of the CNTs. Graft density of modifier and PMMA in various CNTs was evaluated by TGA. Finally, morphology of the CNTs was studied by scanning and transmission electron microscopies.     

PMMA films refractive index modulation via TiO2 nanoparticle inclusions and corona poling

The present study is focused on the characterization of optical properties of poly (methyl methacrylate) (PMMA) films and the possibilities of modulation and fine tuning of their refractive index by the inclusion of different concentrations of nano-sized titanium dioxide (TiO₂) particles (less than 33 nm) and corona poling. The samples are prepared by the “spin coating” method and they are charged in a conventional point-to-plain corona system. The transparent PMMA/TiO₂ films exhibit good optical properties in the visible range. An investigation of the film’s surface refractive index by two wavelengths laser refractometry utilizing the disappearing diffraction pattern method is carried out. The refractive index increases with increasing the TiO₂ content in the nanocomposite films. The corona poling increases the refractive index values for all samples regardless of the polarity and concentration of TiO₂ nanoparticles. The results show that the prepared nanocomposite films have a potential application for optical devices.     

Characterization of poly(2-vinylpyridine)-block-poly(methyl methacrylate) copolymers and blends of their homopolymers by liquid chromatography at critical conditions

Poly(2-vinylpyridine)s (P2VPs) are important polymers with extensive applications in modern day material science. P2VP is an exceptional case for liquid chromatography because of certain polar interactions with most of the stationary phases. In the present study, we established the critical adsorption point (CAP) of P2VP for the first time. The effectiveness of the method is demonstrated by analyses of blends and block copolymers of P2VP and PMMA. The CAP of PMMA is established for determination of molar mass of P2VP component of above mentioned blends and block copolymers. The methods successfully demonstrate the separation of both types of homopolymers from the rest of the samples in conjunction with the determination of molar mass distribution of noncritical block or component. Graphical Abstract

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Evaluation of flame retardancy and shear resistivity characteristics of organoclay within acrylate polymer

The present work focuses on the effect of organically modified nanoclays on the fire resistance and processability characteristics of poly(methyl methacrylate) (PMMA). PMMA nanocomposite of cloisite 30B (methyl tallow bis-2 hydroxyethyl quarternary ammonium salt modifier) (C30B) was prepared by melt blending technique. A comparative study of flame retardant characteristics of virgin and filled matrix was carried out using cone calorimeter at a heat flux of 50 kW m^?2, and the service temperature range was analyzed from thermogravimetric analysis. Parallel plate rheometry revealed the variation in processability as a function of C30B reinforcement and corresponding melt strength of the samples was evaluated through complex viscosity, storage, and loss modulus. Similarly, application-level modulus values were evaluated through viscoelastic properties by dynamic mechanical analysis. Supportive information for the observations from the above characterization was conducted using morphological studies by X-ray diffraction and transmission electron microscopy.     

Facile formation of stimuli-responsive,fluorescent and magnetic nanoparticles based on cellulose stearoyl ester via nanoprecipitation

In comparison to stimuli-responsive, multi-functional nanoparticles (NPs) from synthetic polymers, such NPs based on sustainable, naturally occurring polysaccharides are still scarce. In the present study, stable stimuli-responsive, fluorescent and magnetic NPs were fabricated using cellulose stearoyl esters (CSEs) consisting of cellulose and stearoyl groups. The multifunctional NPs with the average diameters between 80 and 250 nm were obtained after facile nanoprecipitation using CSE solutions containing Fe₃O₄-NPs. Using the aqueous solution of fluorescent rhodamine B as precipitant, NPs with rhodamine B on NP surface were obtained. Rhodamine B could be released depending on the temperature. In comparison, stearoylaminoethyl rhodamine B can be encapsulated in CSE-NPs, which renders obtained NPs reversible fluorescence in response to UV illumination and heat treatment.     

Polyoxotungstate nanoclusters supported on silica as an efficient solid-phase microextraction fiber of polycyclic aromatic hydrocarbons

A highly porous silica-supported tungstophosphoric acid (PW) nanocluster was prepared for use in solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The PWs represent a class of discrete transition metal-oxide nanoclusters and their structures resemble discrete fragments of metal-oxide structures of definite size and shape. Transition metal-oxide nanoclusters display large structural diversity, and their monodisperse sizes can be tuned from several Ångstroms up to 10 nm. The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The nanomaterial was immobilized on a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS. Analytical merits include limits of detection that range from 0.02 to 0.1 pg mL^?1 and a dynamic range as wide as from 0.001 to 100 ng mL^?1. Under optimum conditions, the repeatability for one fiber (n?=?3), expressed as the relative standard deviation, is between 4.3 % and 8.6 %. The method is simple, rapid, and inexpensive. The thermal stability of the fiber and the high relative recovery make this method superior to conventional methods of extraction.

The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS.     

Solid-phase microextraction/gas chromatography–mass spectrometry method optimization for characterization of surface adsorption forces of nanoparticles

A complete characterization of the different physico-chemical properties of nanoparticles (NPs) is necessary for the evaluation of their impact on health and environment. Among these properties, the surface characterization of the nanomaterial is the least developed and in many cases limited to the measurement of surface composition and zetapotential. The biological surface adsorption index approach (BSAI) for characterization of surface adsorption properties of NPs has recently been introduced (Xia et al. Nat Nanotechnol 5:671–675, 2010; Xia et al. ACS Nano 5(11):9074–9081, 2011). The BSAI approach offers in principle the possibility to characterize the different interaction forces exerted between a NP's surface and an organic—and by extension biological—entity. The present work further develops the BSAI approach and optimizes a solid-phase microextraction gas chromatography–mass spectrometry (SPME/GC-MS) method which, as an outcome, gives a better-defined quantification of the adsorption properties on NPs. We investigated the various aspects of the SPME/GC-MS method, including kinetics of adsorption of probe compounds on SPME fiber, kinetic of adsorption of probe compounds on NP's surface, and optimization of NP's concentration. The optimized conditions were then tested on 33 probe compounds and on Au NPs (15 nm) and SiO₂ NPs (50 nm). The procedure allowed the identification of three compounds adsorbed by silica NPs and nine compounds by Au NPs, with equilibrium times which varied between 30 min and 12 h. Adsorption coefficients of 4.66?±?0.23 and 4.44?±?0.26 were calculated for 1-methylnaphtalene and biphenyl, compared to literature values of 4.89 and 5.18, respectively. The results demonstrated that the detailed optimization of the SPME/GC-MS method under various conditions is a critical factor and a prerequisite to the application of the BSAI approach as a tool to characterize surface adsorption properties of NPs and therefore to draw any further conclusions on their potential impact on health. Graphical Abstract

The basic principle of SPME/GC-MS method for characterization of nanoparticles surface adsorption forces     

Impact of PS/SiO2 morphologies on the SERS activity of PS/SiO2/Ag nanocomposite particles

To understand the relationship between the morphology of carboxyl-functionalized polystyrene/silica (PS/SiO₂) nanocomposite microspheres and the surface-enhanced Raman scattering (SERS) performance of PS/SiO₂/Ag nanocomposite particles, core-shell and raspberry-like PS/SiO₂ composite microspheres were used as templates to prepare PS/SiO₂/Ag nanocomposite particles. The core-shell and raspberry-like structured PS/SiO₂ templates were prepared via in situ sol-gel reaction by hydrolysis tetraethyl orthosilicate (TEOS) in alkali solution. Silver nanoparticles (10–50 nm) were loaded on the PS/SiO₂ templates’ surface by chemical reduction. The morphology and structure of the PS/SiO₂/Ag particles were characterized by TEM, SEM, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. Rhodamine 6G (R6G) was selected as a model chemical to study the enhancement performance of substrate constructed by PS/SiO₂/Ag nanocomposite. Results indicated that the PS/SiO₂/Ag nanocomposite prepared based on the core-shell templates showed higher SERS activity. The beneficial effect was associated with a lower specific area of core-shell structure and the larger average diameter of nanosilvers than that of the raspberry-like templates.     

Structural and thermal properties of HDPE/n-AlN polymer nanocomposites

High-density polyethylene (HDPE) containing various volume fractions (0–20 vol%) of aluminum nitride nanoparticles (n-AlN) is prepared by melt mixing. Structural and morphological characterizations of the prepared composites are carried out by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). Thermal stability and degradation kinetics of HDPE/AlN (nano) composites are investigated by Thermogravimetric analysis (TG). HR-TEM micrographs confirm fairly uniform dispersion of AlN nanoparticles, as well as the existence of long interconnected chain-like aggregates. AFM images also confirm homogeneous dispersion of n-AlN in the polymer matrix. Roughness analysis from the AFM data indicates the presence of substantial undulation from the mean surface level. Thermogravimetric data indicate small improvement in the thermal stability of the composites. Kinetic parameters, viz., the activation energy (E _a), frequency factor (A), and reaction order (n) are estimated using the isoconversional methods of Kissinger, Flynn–Wall–Ozawa (FWO), KAS, and Friedman. Activation energies (E _a) calculated by the above four models display nearly similar features and are enhanced by the presence of AlN nanoparticles. Kinetics of degradation of HDPE-AlN (nano) composites follows a first-order reaction.     

Fluorescent protein-based FRET sensor for intracellular monitoring of redox status in bacteria at single cell level

Monitoring of intracellular redox status in a bacterial cell provides vital information about the physiological status of the cell, which can be exploited in several applications such as metabolic engineering and computational modeling. Fluorescent protein-based genetically encoded sensors can be used to monitor intracellular oxidation/reduction status. This study reports the development of a redox sensor for intracellular measurements using fluorescent protein pairs and the phenomenon of Förster resonance energy transfer (FRET). For the development of the sensor, fluorescent proteins Citrine and Cerulean were genetically modified to carry reactive cysteine residues on the protein surface close to the chromophore and a constructed FRET pair was fused using a biotinylation domain as a linker. In oxidized state, the FRET pairs are in close proximity by labile disulfide bond formation resulting in higher FRET efficiency. In reducing environment, the FRET is diminished due to the increased distance between FRET pairs providing large dynamic measurement range to the sensor. Intracellular studies in Escherichia coli mutants revealed the capability of the sensor in detecting real-time redox variations at single cell level. The results were validated by intensity based and time resolved measurements. The functional immobilization of the fluorescent protein-based FRET sensor at solid surfaces for in vitro applications was also demonstrated. Graphical Abstract

Schematic representation of FRET-based redox sensor     

Heat of reaction and curing of epoxy resin

The heat of reaction and kinetics of curing of diglycidyl ether of bisphenol-A (DGEBA) type of epoxy resin with catalytic amounts of ethylmethylimidazole (EMI) have been studied by differential power-compensated calorimetry as a part of the program for the study of process monitoring for composite materials. The results were compared with those from 1∶1 and 1∶2 molar mixtures of DGEBA and EMI. A method of determination of heat of reaction from dynamic thermoanalytical instruments was given according to basic thermodynamic principles. The complicated mechanism, possibly involving initial ionic formation, has also been observed in other measurements, such as by time-domain dielectric spectroscopy. The behavior of commercially available DGEBA resin versus purified monomeric DGEBA were compared. The melting point of purified monomeric DGEBA crystals is 41.4 °C with a heat of fusion of 81 J/g. The melt of DGEBA is difficult to crystallize upon cooling. The glass transition of purified DGEBA monomer occurs around ?22 °C with aΔC _p of 0.60 J/K/g.     

Quantitative characterization by asymmetrical flow field-flow fractionation of IgG thermal aggregation with and without polymer protective agents

Complexes formed between poly(acrylates) and polyclonal immunoglobulin G (IgG) in its native conformation and after heat stress were characterized using asymmetric flow field-flow fractionation (AF4) coupled with on-line UV-Vis spectroscopy and multi-angle light-scattering detection (MALS). Mixtures of IgG and poly(acrylates) of increasing structural complexity, sodium poly(acrylate) (PAA), a sodium poly(acrylate) bearing at random 3 mol % n-octadecyl groups, and a random copolymer of sodium acrylate (35 mol %), N-n-octylacrylamide (25 mol %) and N-isopropylacrylamide (40 mol %), were fractionated in a sodium phosphate buffer (0.02 M, pH 6.8) in the presence, or not, of 0.1 M NaCl. The AF4 protocol developed allowed the fractionation of solutions containing free poly(acrylates), native IgG monomer and dimer, poly(acrylates)/IgG complexes made up of one IgG molecule and a few polymer chains, and/or larger poly(acrylates)/IgG aggregates. The molar mass and recovery of the soluble analytes were obtained for mixed solutions of poly(acrylates) and native IgG and for the same solutions incubated at 65 °C for 10 min. From the combined AF4 results, we concluded that in solutions of low ionic strength, the presence of PAA increased the recovery ratio of IgG after thermal stress because of the formation of electrostatically-driven PAA/IgG complexes, but PAA had no protective effect in the presence of 0.1 M NaCl. Poly(acrylates) bearing hydrophobic groups significantly increased IgG recovery after stress, independently of NaCl concentration, because of the synergistic effect of hydrophobic and electrostatic interactions. The AF4 results corroborate conclusions drawn from a previous study combining four analytical techniques. This study demonstrates that AF4 is an efficient tool for the analysis of protein formulations subjected to stress, an important achievement given the anticipated important role of proteins in near-future human therapies. ?      

Thermogravimetric analysis of the desorption of iodine from ion-exchange resins

A method was developed for the evaluation of isothermal and dynamic thermogravimetric measurements of the desorption of low molecular weight compounds dissolved in polymers. The method is based on a solution of the non-linear equation for the diffusion of the low molecular weight compounds. Experimental data were analyzed for the desorption of alcohol from PMMA and of iodine from ion-exchange resins, the latter being strongly influenced by the degree of association of the polyiodide in the anions.     

Visual detection of arginine,histidine and lysine using quercetin-functionalized gold nanoparticles

We report on the use of quercetin-functionalized gold nanoparticles (QC-AuNPs) as a colorimetric probe for the amino acids arginine (Arg), histidine (His) and lysine (Lys). The method is based on the aggregation of the QC-AuNPs that is caused by these amino acids and leads to a visually detectable color change from red to blue. The absorption maxima shift from 525 nm to 702, 693, and 745 nm, respectively. Aggregations are confirmed by dynamic light scattering (DLS) and transmission electron microscopic techniques (TEM). The effects of the QC concentration, temperature and reaction time for the preparation of QC-Au NPs were tested. Other amino acids do not interfere. Under the optimal conditions, linear relationships exist between the absorption ratios at 702/525 nm (for Arg), 693/525 nm (for His), and 745/525 nm (for Lys) over the concentrations ranges from 2.5–1,250 μM (Arg) and 1–1,000 μM (His and Lys), respectively. The respective limits of detection are 0.04, 0.03, and 0.02 μM. The method provides a useful tool for the rapid visual and instrumental determination of the three amino acids. Figure

We report the use of quercetin as novel reagent for preparation and functionalization of gold nanoparticles to colorimetric sensing of three aminoacids (arginine, histidine and lysine). This is based on the aggregation of QC-AuNPs induced by three aminoacids.