Galactose Oxidase/Prussian Blue Based Biosensors

This paper describes the development of an amperometric biosensor based on galactose oxidase (GAOx) immobilization within a laponite clay film deposited on Carbon Screen‐Printed Electrodes modified by electrodeposited Prussian Blue and coated with poly‐(O‐phenylenediamine) (PPD/PB/CSPEs). Amperometric performances of GAOx@laponite/PPD/PB/CSPEs bioelectrodes were determined using several GAOx substrates. Using these modified electrodes the reduction of enzymatically generated hydrogen peroxide was performed at ?0.2 V vs. Ag‐AgCl. In an initial attempt, E.Coli transketolase activity on its immobilized form was followed using a bienzymatic GAOx‐TK biosensor.     

Synthesis and electrorheological response of nano-sized laponite stabilized poly(methyl methacrylate) spheres

Poly(methyl methacrylate) (PMMA) nanospheres were fabricated via surfactant-free Pickering emulsion polymerization, in which hydrophilic laponite clay was used to stabilize the emulsions of methyl methacrylate dispersed in distilled water. These synthesized PMMA nanoparticles, of which the surface is compactly wrapped by laponite clay, are observed, as confirmed by scanning electron microscopy and transmission electron microscope images. Fourier-transform infrared spectra and thermogravimetry analysis confirm the chemical composition, thermal property, and mass percent of the laponite located on the surface of PMMA particles. Finally, laponite-wrapped nano-sized PMMA spheres were adopted as an electrorheological material. By using an optical microscope, the chain-like structure was observed when an external electric field was applied. In addition, the ER performance was also examined via a rotational rheometer equipped with a high voltage generator.     

A kinetic investigation of surfactant‐free emulsion polymerization of styrene using laponite clay platelets as stabilizers

We report the kinetics and mechanism of soap‐free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, $ \bar n $ , was found to be high in the range 3–6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Competition between entropy and electrostatic interactions in a binary colloidal mixture of spheres and platelets

We describe the phase behavior of an aqueous mixture of discotic nanoparticles of laponite and spherical magnetic nanoparticles of maghemite. To obtain stable mixtures from a chemical point of view, the maghemite nanoparticles are first coated by a thin layer of silica in order to adapt their surface chemistry to that of laponite nanoparticles: this enables one to raise volume fractions of maghemite Phi mag in the laponite suspensions up to several percent. Although the system is out of equilibrium, a "fluid-solid" state diagram was established showing that the mixtures undergo a fluid-solid transition, similar to that of pure suspensions of laponite, over a given volume fraction of laponite Phi lap and over a given Phi mag. An increase in Phi mag shifts Phi lap toward the lower values. When a solid sample is just above Phi lap, the application of an external magnetic field gradient induces a solid-to-liquid transition if the sample is located not too far from Phi lap on the state diagram. The structure of the mixtures, determined either at small scale by small-angle neutron scattering (SANS) or at intermediate scales by optical microscopy, shows that the solid samples are phase separated at a local scale: they are made of densely connected domains of laponite nanoparticles surrounding liquid pockets of maghemite nanoparticles. The size of the pockets grows with time. The magnetic liquid pockets are responsible for the rupture of the solid samples when an external magnetic field gradient is applied since their deformation induces local mechanical stress, internally damaging the network formed by the solid domains of laponite. The microscopic phase separation is the result of two opposite effects: (i) entropic effects that tend to phase separate the system macroscopically when the packing entropy overcomes the orientational entropy and (ii) long-range electrostatic repulsions that freeze the system.     

Highly filled polystyrene-laponite nanocomposites prepared by emulsion polymerization

Polystyrene-based nanocomposite films containing up to 20 wt% laponite clay have been prepared by emulsion polymerization. Significant increases in the storage and tensile moduli were observed in both the glassy and rubbery state on laponite addition. However, whereas in the glassy state these increases were correlated with the extent of exfoliation of the laponite, in the rubbery state they were more dependent on the overall laponite content. These results are discussed in terms of the observed morphologies and micromechanical models for the reinforcing effect of rigid nano-sized filler particles.     

合成锂皂石分散体系

综述了合成锂皂石在水中的分散及其分散体系的胶体和流变学性质。重点介绍了改变离子强度、pH、温度以及添加表面活性剂对合成锂皂石分散体系性质的影响和研究进展。     

Copper acetylacetonate anchored onto amine-functionalised clays

Copper (II) acetylacetonate was immobilised directly onto two clays, laponite (Lap) and K10-montmorillonite (K10), and after their amine functionalisation with (3-aminopropyl)triethoxysilane (APTES). All the materials were characterised by nitrogen adsorption isotherms at -196 degrees C, elemental analysis, TG-DSC, XRD, and IR spectroscopy. The K10-based materials were also characterised by XPS. The APTES-functionalised K10 showed higher copper loading than K10, indicating that the clay functionalisation enhanced the complex immobilisation; on the contrary, in Lap-based materials higher metal content was obtained by direct complex anchoring, probably due to the delaminated nature of Lap which induced the particles aggregation on functionalisation with APTES. All the results pointed out that the Cu complex was anchored onto the amine-functionalised clays by Schiff condensation between the amine groups of anchored APTES and the carbonyl groups of the acetylacetonate ligand, whereas direct immobilisation proceeded mostly through interaction between the metal centre and the clay surface hydroxyl groups.     

Model for cage formation in colloidal suspension of laponite

In this paper we investigate glass transition in aqueous suspension of synthetic hectorite clay, laponite. We believe that upon dispersing laponite clay in water, the system comprises of clusters (agglomerates) of laponite dispersed in the same. Subsequent osmotic swelling of these clusters leads to an increase in their volume fraction. We propose that this phenomenon is responsible for slowing down of the overall dynamics of the system. As clusters fill up the space, the system undergoes glass transition. Along with the mode coupling theory, the proposed mechanism rightly captures various characteristic features of the system in the ergodic regime as it approaches glass transition.     

Fluorescence Resonance Energy Transfer between organic dyes adsorbed onto nano-clay and Langmuir–Blodgett (LB) films

In this communication we investigate two dyes N,N′-dioctadecyl thiacyanine perchlorate (NK) and octadecyl rhodamine B chloride (RhB) in Langmuir and Langmuir–Blodgett (LB) films with or with out a synthetic clay laponite. Observed changes in isotherms of RhB in absence and presence of nano-clay platelets indicate the incorporation of clay platelets onto RhB-clay hybrid films. AFM images confirm the incorporation of clay into hybrid films. FRET is observed in clay dispersion and LB films with and without clay. Efficiency of energy transfer is maximum in LB films with clay.     

Effect of added salt on the depletion attraction caused by non-adsorbing clay particles

Total internal reflection microscopy (TIRM) has been used to study the effect of a model clay colloid (laponite) on the interparticle forces acting between a 6 μm polystyrene sphere and a glass slide when the two are separated by 50–350 nm of an aqueous solution containing up to 1 mM of NaCl. In the absence of clay, the Brownian sphere samples elevations in the vicinity of the secondary minimum formed by gravitational attraction, van der Waals attraction and double-layer repulsion. The addition of clay induces a discernible depletion attraction at concentrations greater than 100 ppm and for separation distances as large as 200 nm, which greatly exceeds the diameter of the laponite disks (25 nm). Increasing the clay concentration increases the magnitude of this attraction without changing the range (defined as the largest separation distance at which the attractive potential is 1 kT). Increasing the concentration of an indifferent electrolyte (NaCl) reduces both the magnitude and range of the depletion attraction. These observations are in quantitative agreement with the primitive theory in which depletion attraction is computed as the product of the osmotic pressure of the polyelectrolyte (calculated from Donnan’s equation) and the area of overlap of the depletion layers. Besides the effect of the polyelectrolyte on the Debye length, the only adjustable parameter is the depletion layer thickness or ‘effective radius’ of the platelets which is found to be the radius of the laponite disks plus five Debye lengths.     

Electrochemical deposition and characterization of NiCu coatings as cathode materials for hydrogen evolution reaction

In this study, NiCu composite coatings were electrochemically deposited on a copper electrode (Cu/NiCu) and characterized by atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) techniques in view of their possible applications as electrocatalytic materials for the hydrogen evolution reaction (HER). The HER activity of the prepared electrodes were studied in 1 M KOH solution by cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that, the NiCu coating has a porous structure and good electrocatalytic activity for the HER in alkaline medium. The HER activity of the Cu/NiCu electrode was higher than uncoated (Cu) and Ni coated (Cu/Ni) copper electrodes. Its catalytic activity was related to the porosity as well as synergistic interaction of Ni and Cu.     

Photoinduced electron transfer reactions at methylene blue adsorbed nafion and clay coated electrodes

Nafion and montmorillonite clay adsorbed methylene blue coated onto platinum electrode were prepared. These dye modified electrodes were used as photoelectrodes in a photogalvanic cell in the presence of Fe²⁺ ions. The photoelectrochemical investigations showed that the dye coated electrodes behaved as cathode upon irradiation whereas the plain platinum electrode dipped in a homogeneous solution containing methylene blue and Fe²⁺ ions behaved as anode. It is suggested that the intermediate complex formed between the photoreduced methylene blue and ferric ion lead to the reductive reaction at the coated electrode.     

Nanoparticle-reinforced associative network hydrogels

ABA triblock copolymers in solvents selective for the midblock are known to form associative micellar gels. We have modified the structure and rheology of ABA triblock copolymer gels comprising poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) through addition of a clay nanoparticle, laponite. Addition of laponite particles resulted in additional junction points in the gel via adsorption of the PEO corona chains onto the clay surfaces. Rheological measurements showed that this strategy led to a significant enhancement of the gel elastic modulus with small amounts of nanoparticles. Further characterization using small-angle X-ray scattering and dynamic light scattering confirmed that nanoparticles increase the intermicellar attraction and result in aggregation of PLA-PEO-PLA micelles.     

Cation and anion exchange on clay modified electrodes

Carbon paste electrodes modified with clay minerals were used for the study of ion-exchange properties of these clay minerals. Cation exchange of Cu(II) was studied by the dependence on the pH, ionic strength and the form of the minerals. The highest anionic exchange of Hg(II) acetates and chlorides was found on montmorillonites. Anionic exchange of Au(III) chloro complexes was found on montmorillonite, but their sorption is strongly influenced by other anions such as chlorides and thiocyanates. The results found are important with regard to the study of the anion-exchange properties of clay minerals. Received: 2 December 1999 / Accepted: 2 March 2000     

Electrochemical nitrate biosensor based on poly(pyrrole-viologen) film-nitrate reductase-clay composite

The immobilization of nitrate reductase (NR) was performed by entrapment in a laponite clay gel and cross-linking by glutaraldehyde. In presence of nitrate and methyl viologen, a catalytic current appeared at -0.60 V illustrating the enzymatic reduction of nitrate into nitrite via the reduced form of the freely diffusing methyl viologen. The electropolymerization of a water-soluble pyrrole viologen derivative within the interlamellar spaces and channels of the host clay matrix successfully carried out the electrical wiring of the entrapped NR. Rotating disk measurements led to the determination of kinetic constants, namely k(2)=10.7 s(-1) and K(M)=7 microM. These parameters reflect the efficiency of the electro-enzymatic reduction of nitrate and the substrate affinity for the immobilized enzyme.     

Enhanced Direct Electron Transfer of a Multihemic Nitrite Reductase on Single‐walled Carbon Nanotube Modified Electrodes

Single‐walled carbon nanotubes (SWCNTs) deposits on glassy carbon and pyrolytic graphite electrodes have dramatically enhanced the direct electron transfer of the multihemic nitrite reductase from Desulfovibrio desulfuricans ATCC 27774, enabling a 10‐fold increase in catalytic currents. At optimal conditions, the sensitivity to nitrite and the maximum current density were 2.4±0.1 A L mol^?1 cm^?2 and 1500 µA cm^?2, respectively. Since the biosensor performance decreased over time, laponite clay and electropolymerized amphiphilic pyrrole were tested as protecting layers. Both coating materials increased substantially the bioelectrode stability, which kept about 90 % and 60 % of its initial sensitivity to nitrite after 20 and 248 days, respectively.     

Voltammetric Sensing of Mercury and Copper Cations at Poly(EDTA‐like) Film Modified Electrode

Complexing polymer‐coated electrodes have been synthesized by oxidative electropolymerization of ethylenediamine tetra‐N‐(3‐pyrrole‐1‐yl)propylacetamide (monomer L ). The presence of four polymerizable pyrrole fragments on the same EDTA skeleton was thought to confer enhanced rigidity and controlled dimensionality to the resulting complexing materials, which were used for the electrochemical detection of Hg(II), Cu(II), Pb(II) and Cd(II) ions by means of the chemical preconcentration‐anodic stripping technique. The polyamide electrode material showed particularly a significant selectivity towards mercury ions, even in the presence of a large excess of other metal cations. Moreover, the use of imprinted polymer‐coated electrodes prepared by electropolymerization of L in the presence of metal cations turned out to significantly improve the detection limits, down to 5×10^?10 mol L^?1 for Hg(II) and Cu(II) species.     

PVC-laponite nanocomposites: Enhanced resistance to UV radiation

Laponite, a clay mineral, was treated by intercalation of two different phthalocyanine amide polymers based on aliphatic amine (MF-PcAl) as well as an aromatic one (MF-PcAr). The intercalation of the amide polymers was followed by X-ray diffraction (XRD). The different forms of laponite even in its untreated form were incorporated into poly(vinyl chloride) (PVC) formulations via melt blending method to produce PVC-laponite nanocomposites of exfoliated type which was confirmed by XRD. The stabilization mode of the incorporated laponites against UV radiation is discussed based on scanning electron microscopy (SEM), XRD, UV-vis absorption and transmission spectra, electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and mechanical properties. Improved resistance to the UV degradative effect was explained on the light of the ability of the clay to scatter the light and to trap any growing radicals as well in addition to the sacrificing role of phthalocyanines by absorbing the incident light on the expense of the PVC and transmitting the rest of the light in another non-harmful form such as heat.     

Graphene arrested in laponite-water colloidal glass

Graphene production in water from graphite sources is an important technological route toward harvesting the unique properties of this material. Graphene forms thermodynamically unstable dispersions in water, limiting the use of this solvent due to aggregation. We show that graphene-water dispersions can be controlled kinetically to produce graphene by using laponite clay. Laponite exhibits rapid gelation kinetics when dispersed in water above its gelation concentration, allowing graphene aggregation to be halted after exfoliation in water at ambient conditions. The transparency of laponite colloidal glass and films is important in examining the extent of graphene exfoliation.     

Electropolymerized coatings of polyaniline on copper by using the galvanostatic method and their corrosion protection performance in HCl medium

The synthesis of polyaniline coatings on the copper (Cu) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by Fourier transform infrared spectroscopy, UV–visible absorption spectrometry and scanning electron microscopy. The anticorrosion performances of polyaniline coatings were investigated in 0.5 M HCl medium by the potentiodynamic polarization technique and electrochemical impedance spectroscopy. The corrosion rate of polyaniline‐coated Cu was found to be ～27 times lower than bare Cu, and potential corrosion increased from ?0.21 V versus Ag/AgCl for uncoated Cu to ?0.19 V versus Ag/AgCl for polyaniline‐coated Cu electrodes. Electrochemical measurements indicate that polyaniline coating has good inhibiting properties with a mean efficiency of ~96% at 10 mAcm^?2 current density applied on Cu corrosion in acid media. The results of this study clearly ascertain that the polyaniline has an outstanding potential to protect Cu against corrosion in an acidic environment. Copyright © 2014 John Wiley & Sons, Ltd.