Pt nanoflower/polyaniline composite nanofibers based urea biosensor

Hybrid materials with special structures are of great interest because of their superior properties compared with their pure counterparts. Hybrid polyaniline (PANi) nanofibers with integrated Pt nanoflowers are studied in this research. PANi is prepared by in situ polymerization of aniline on an electrospun nanofiber template in an acidic solution with ammonium persulfate (APS) as the oxidant. Pt nanoflowers are further electrodeposited onto the PANi nanofibers backbone by cyclic voltammetry (CV), resulting in novel functionalized hybrid nanofibers. The coverage of Pt nanoflowers on PANi nanofibers can be facilely controlled by adjusting the electrodeposition conditions. The factors affecting Pt nanoflowers formation are further investigated. As a demonstration, urease is immobilized onto the Pt/PANi hybrid nanofibers and the composite was employed as the sensing platform for urea detection in a flow-injection-analysis (FIA) system. The detection of urea shows a wide linear range (up to 20 mM), a good limit of detection of 10 μM (S/N=3), and an excellent anti-interference property against chloride ion. In addition, it was found that the response to urea was attributed not only to the conductivity change of PANi due to the interaction between PANi and ammonia (liberated from the enzymatic reaction), but also to the interaction between Pt nanoflowers and amine groups in urea. The strategy developed in this study can be extended to synthesize other composite nanofibers consisting of conducting polymer and metal nanoparticles for a wide range of sensing applications.     

Study of water sorption on modified Agave fibres

Polymer composite materials are usually reinforced by synthetic matter such as carbon or glass fibres. However, owing to their good mechanical properties and low density, natural fibres are now increasingly being considered as reinforcement. With the aim of a new natural fibre based composite, various chemical treatments have been performed on Agave (Americana L.) fibres in order to improve their compatibility with the polymer matrix and to reduce their affinity for water. The effect of these treatments on the fibre water sorption power has been investigated by means of a micro-balance. Equilibrium water sorption isotherms have been deduced from weight variations of the fibres under water vapor pressure increments. Several specific physico-chemical models have been tested to describe the water sorption isotherms. The Park’s model was found to describe the experimental results accurately and over a wide activity range. The sorption kinetics was also exploited in order to evaluate the diffusivity of water in the fibres. The variation of the water diffusion coefficient with water concentration is in agreement with the triple sorption mode described by the Park’s model. These results show a global increase of moisture resistance of the fibres after chemical treatment. This effect is interpreted in terms of chemical and structural modifications of the cell-wall structure.     

Combinatorial polymer electrospun matrices promote physiologically-relevant cardiomyogenic stem cell differentiation

Myocardial infarction results in extensive cardiomyocyte death which can lead to fatal arrhythmias or congestive heart failure. Delivery of stem cells to repopulate damaged cardiac tissue may be an attractive and innovative solution for repairing the damaged heart. Instructive polymer scaffolds with a wide range of properties have been used extensively to direct the differentiation of stem cells. In this study, we have optimized the chemical and mechanical properties of an electrospun polymer mesh for directed differentiation of embryonic stem cells (ESCs) towards a cardiomyogenic lineage. A combinatorial polymer library was prepared by copolymerizing three distinct subunits at varying molar ratios to tune the physicochemical properties of the resulting polymer: hydrophilic polyethylene glycol (PEG), hydrophobic poly(ε-caprolactone) (PCL), and negatively-charged, carboxylated PCL (CPCL). Murine ESCs were cultured on electrospun polymeric scaffolds and their differentiation to cardiomyocytes was assessed through measurements of viability, intracellular reactive oxygen species (ROS), α-myosin heavy chain expression (α-MHC), and intracellular Ca(2+) signaling dynamics. Interestingly, ESCs on the most compliant substrate, 4%PEG-86%PCL-10%CPCL, exhibited the highest α-MHC expression as well as the most mature Ca(2+) signaling dynamics. To investigate the role of scaffold modulus in ESC differentiation, the scaffold fiber density was reduced by altering the electrospinning parameters. The reduced modulus was found to enhance α-MHC gene expression, and promote maturation of myocyte Ca(2+) handling. These data indicate that ESC-derived cardiomyocyte differentiation and maturation can be promoted by tuning the mechanical and chemical properties of polymer scaffold via copolymerization and electrospinning techniques.     

Composite matrix membranes as synthetic receptor systems. 2. Structural-morphological characteristics

Structural and morphological characteristics of composite imprinted membranes for selective recognizing of adenosine 3',5'-cyclic monophosphate (cAMP) were studied. Composite polyvinylidene fluoride microfiltration membranes (Millipore) covered with a thin imprinted polymer layer were prepared using photoinitiated copolymerization of dimethylaminoethylmetacrylate with trimethylolpropanethrimethacrylate in the presence of cAMP as template. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to visualise surfaces and cross-sections of imprinted membranes and to determine their structural and morphological parameters such as pore size, thickness of selective imprinted layer, surface roughness as well as total surface contact area. The impact of structural characteristics on separation properties of the imprinted membranes was analyzed. It was found out that the thickness of the imprinted polymer layer with optimal recognizing properties is limited.     

DNA immobilization/hybridization on plasma-polymerized pyrrole

The present work describes the fabrication and characterization of the conducting polymer coatings prepared by the continuous wave plasma polymerization and the applications as adhesion layers for studying DNA immobilization/hybridization. The stability of plasma polymerized pyrrole (ppPY) in the aqueous solution was characterized by ellipsometry. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate polymer matrix properties and oligonucleotide/DNA binding interaction. The successful DNA immobilization on ppPY surfaces was found to depend on the macromolecular architecture of plasma polymerized films. The plasma polymers with similar thickness deposited at different input powers showed various comparable immobilization properties. The plasma-polymerized films prepared at the low input power showed a lower sensitivity toward DNA binding than those films deposited at the high input power. This result will be important to study plasma polymerized films as potential DNA biosensors in the future.     

Recent advances in polyaniline based biosensors

The present paper contains a detailed overview of recent advances relating to polyaniline (PANI) as a transducer material for biosensor applications. This conducting polymer provides enormous opportunities for binding biomolecules, tuning their bio-catalytic properties, rapid electron transfer and direct communication to produce a range of analytical signals and new analytical applications. Merging the specific nature of different biomolecules (enzymes, nucleic acids, antibodies, etc.) and the key properties of this modern conducting matrix, possible biosensor designs and their biosensing characteristics have been discussed. Efforts have been made to discuss and explore various characteristics of PANI responsible for direct electron transfer leading towards fabrication of mediator-less biosensors.     

Overoxidized polypyrrole film directed single-walled carbon nanotubes immobilization on glassy carbon electrode and its sensing applications

In this paper, the films of overoxidized polypyrrole (PPyox) directed single-walled carbon nanotubes (SWNTs) have been electrochemically coated onto glassy carbon electrode (GCE). Electroactive monomer pyrrole was added into the solution containing sodium dodecyl sulfate (SDS) and SWNTs. Then, electropolymerization was proceeded at the surface of GCE, and a novel kind of conducting polymer/carbon nanotubes (CNTs) composite film with the orientation of CNTs were obtained correspondingly. Finally, this obtained polypyrrole (PPy)/SWNTs film modified GCE was oxidized at a potential of +1.8 V. It can be found that this proposed PPyox/SWNTs composite film modified GCE exhibited excellent electrocatalytic properties for some species such as nitrite, ascorbic acid (AA), dopamine (DA) and uric acid (UA), and could be used as a new sensor for practical applications. Compared with previous CNTs modified electrodes, SWNTs were oriented towards the outside of modified layer by PPyox and SDS, which made the film easily conductive. Moreover, this proposed film modified electrode was more stable, selective and applicable.     

Rheological behaviour of a succinoglycan polysaccharide in dilute and semi-dilute solutions

We report the rheological behaviour of a succinoglycan polysaccharide in dilute and semi-dilute solutions as a function of temperature, ionic strength and the nature of counterion. We have examined the viscosity dependence as a function of molecular weight using samples obtained by ultrasonication. We have also prepared samples lacking succinate substitutes and compared their behaviour with that of the native polymer. In both cases, we observed that, after heating a polymer solution for the first time above the conformational transition temperature, a different ordered state was obtained on cooling. This state had a lower molecular weight and intrinsic viscosity but identical chemical structure and local properties. A role for the side chain in the stabilization of breaks in the backbone is suggested. Nevertheless, a unique curve is obtained for the specific viscosity as a function of the overlap parameter c[eta] for different polymer concentrations of both the native and heated forms. However, different curves are obtained for normal and succinate-free polymers, and the succinate-free polymer is characterized by a lower Huggins constant.     

Pt based enzyme electrode probes assembled with Prussian Blue and conducting polymer nanostructures

Conductive polymer nanotubules of 1,2-diaminobenzene (1,2-DAB) were prepared using a porous polycarbonate membrane template, placed on a Pt foil and used to support the polymer, then, the electropolymerisation was performed by chronocoulometry. The obtained conductive polymer nanostructures were then placed on Pt electrode and used to support highly dispersed prussian blue (PB), which acts as the active component for H2O2 detection. The observed good stability of PB as catalyst of H2O2 was related to the presence of organic non-conventional conducting polymers in a composite nanostructured film. These nanostructured polymer/PB composite films were also characterised by scanning electron microscopy (SEM) and Raman spectroscopy. The non-conventional conducting polymer nanotubules/PB modified Pt electrodes were tested by cyclic voltammeter for stability at different pH values, then, by amperometry, for hydrogen peroxide, ascorbic acid, acetaminophen, uric acid and acetylcholine. Glucose oxidase (GOD), lactate oxidase (LOD), L-amino acid oxidase (L-AAOD), alcohol oxidase (AOD), glycerol-3-phosphate oxidase (GPO), lysine oxidase (LyOx), and choline oxidase (ChOx) were immobilised on PB layer supported on 1,2-diaminobenzene (1,2-DAB) nanotubules onto the Pt electrodes. Different strategies for enzyme immobilisation were performed and used. Analytical parameters such as reproducibility, interference rejection, response time, storage and operational stability of the sensors have been studied and optimised. Results provide a guide to design high sensitive, stable and interference-free biosensors. The glucose biosensors assembled with nanostructured poly(1,2-DAB) showed a detection limit of 5 x 10(-5) mol l(-1), a wide linearity range (5 x 10(-5) to 5 x 10(-3) mol l(-1)), a high selectivity, a stability of 3 months at 4 degrees C, and at least 4 weeks at room temperature. Similar analytical parameters and stability were also studied for L-(+)-lactic acid, L-leucine, ethanol, glycerol-3-phosphate, lysine, and choline biosensors.     

Contributions of polystyrene to the mechanical properties of blended mixture of old newspaper and wood pulp

Composites from recycled newspaper would result in the effective use of the waste product which is currently burned or land-filled, as well as potential reduction in the cost of manufactured composite. In this work, old newspaper (ONP) together with yellowish wood pulp and waste polystyrene from packaging were used to produce composite. The technique studied in this work is an alternative to the conventional melt compounding and was expected to provide efficient wetting of fibers by the polymer. Polystyrene was grafted with acrylonitrile, ethylmethacrylate and butylmethacrylate, respectively, using benzoyl peroxide as an initiator. The amount of polystyrene to monomer is 1:0.75 and to initiator is 1:1. The grafted copolymers were characterized using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Different ratios of waste polystyrene or grafted waste polystyrene were mixed with a blend of old newsprint and wood pulp to form composites. The mechanical properties of these composites as well as water uptake were studied. The tensile properties of the prepared composites did not show essential improvement, except for the modulus of elasticity. Scanning electron microscopy indicate that composites with grafted polystyrene showed more homogeneity than the composite with polystyrene and also than blank, so the grafted polymer is distributed very well improving the mechanical properties of the composites. Strong adhesion between the fiber and grafted polymer was found.     

Polyvalent side chain peptide-synthetic polymer conjugates as HIV-1 entry inhibitors

This report describes the synthesis and properties of a series of polyvalent side chain peptide-synthetic polymer conjugates designed to block the CD4 binding site on gp120 and inhibit HIV-1 entry into a host cell. The peptide sequences in the conjugates are based on the CDR H3 region of the neutralizing anti-HIV-1 antibody IgG1 b12. Using a consecutive ester-amide/thiol-ene postpolymerization modification strategy, a library of polymer conjugates was prepared. Evaluation of the HIV-1 inhibitory properties revealed that midsized polymer conjugates displayed the highest antiviral activity, while shorter and longer conjugates proved to be less efficacious inhibitors. The lower molecular weight conjugates may not have sufficient length to span the distance between two neighboring gp120 containing spikes, while the higher molecular weight conjugates may be compromised due to a higher entropic penalty that would accompany their binding to the viral envelope. Although the IC(50) values for these polymer conjugates are higher than that of the parent IgG1 b12 antibody, the strategy presented here may represent an interesting antiviral approach due to the attractive properties of such polymer therapeutics (relatively inexpensive production and purification costs, high thermal and chemical stability in storage conditions, long half-life in biological tissues, low immunogenicity, and protection from proteolytic degradation).     

Quantum dot-containing polymer particles with thermosensitive fluorescence

Composite polymer particles consisting of a solid poly(acrolein-co-styrene) core and a poly(N-vinylcaprolactam) (PVCL) polymer shell doped with CdSe/ZnS semiconductor quantum dots (QDs) were fabricated. The temperature response of the composite particles was observed as a decrease in their hydrodynamic diameter upon heating above the lower critical solution temperature of the thermosensitive PVCL polymer. Embedding QDs in the PVCL shell yields particles whose fluorescence is sensitive to temperature changes. This sensitivity was determined by the dependence of the QD fluorescence intensity on the distances between them in the PVCL shell, which reversibly change as a result of the temperature-driven conformational changes in the polymer. The QD-containing thermosensitive particles were assembled with protein molecules in such a way that they retained their thermosensitive properties, including the completely reversible temperature dependence of their fluorescence response. The composite particles developed can be used as local temperature sensors, as carriers for biomolecules, as well as in biosensing and various bioassays employing optical detection schemes.     

One-step co-electropolymerized conducting polymer-protein composite film for direct electrochemistry-based biosensors

A novel meliorative conducting polymer-redox protein composite film was fabricated via one-step co-electropolymerization approach. With electrostatic interactions between the conducting polymer and the protein, the composite film possesses attractive features, especially in studies of direct electron transfer of redox proteins as well as the development of unique protein based biosensors. Electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), reflectance absorption infrared spectroscopy (RAIR) and ultraviolet visible spectroscopy (UV-vis) were performed to characterize the unique film. The direct electron transfer of the redox protein in the composite film were explored, and its bioactivity was also investigated by catalyzing the reductions of H(2)O(2) and NO(2)(-), demonstrating its great potential applications in direct electrochemistry-based high performance biosensors.     

Fe3O4/ 生物可降解复合材料研究

磁性氧化铁纳米粒子因具有尺寸小、低毒性和超顺磁性等特点,已经引起了生物化工、医药工业领域的广泛关注。生物可降解高分子材料是生物医用高分子研究中最活跃的领域之一,已广泛用于外科手术缝合线,植入体材料及药物释放载体等。将Fe3O4和生物可降解高分子材料进行复合,可以扩大两者的应用范围,达到理想的治疗效果,并有望开创临床治疗的新时代。本文介绍了磁性四氧化三铁粒子的化学制备方法,包括共沉淀法、溶胶-凝胶法、微乳液法,并对各种方法的优缺点进行了比较;重点阐述了磁性壳聚糖,磁性聚乳酸,磁性PEG,磁性PCL复合材料的制备,及它们在酶的固定化、磁靶向药物及基因载体等医学领域的应用,显示了Fe3O4/生物可降解复合材料在医学领域的广阔应用前景;最后对复合材料走向临床应用所面临的问题及发展前景进行了讨论。     

Bacterial cellulose nanocrystals exhibiting high thermal stability and their polymer nanocomposites

Nanocrystals prepared from bacterial cellulose are considered as 'green nanomaterials' depending on their renewable nature and ease of production without the involvement of hazardous chemical treatments. In this investigation, a top down approach was followed for the preparation of bacterial cellulose nanocrystals (BCNC) using a commercially available cellulase enzyme so as to retain native properties of bacterial cellulose even in its nanodimensional form. The morphological and dimensional parameters of BCNC were studied using atomic force microscope (AFM) and transmission electron microscope (TEM). Thermal properties of BCNC produced using the novel enzyme treatment and conventional sulfuric acid hydrolysis were compared. The thermal stability of enzyme processed BCNC was almost two fold higher than sulfuric acid processed ones. Further, the activation energy required for decomposition of enzyme processed BCNC was much higher than the other. Using this enzyme processed BCNC, Polyvinylalcohol (PVA) nanocomposite films were prepared and characterized. Incorporation of these nanocrystals in polymer matrix resulted in a remarkable improvement in the thermal stability as well as mechanical properties of nanocomposite films. These nanocomposites exhibited higher melting temperature (Tm) and enthalpy of melting (ΔHm) than those of pure PVA, suggesting that the addition of nanocrystals modified the thermal properties of PVA. The effective load transfer from polymer chains to the BCNC resulted in an improved tensile strength from 62.5 MPa to 128 MPa, by the addition of just 4 wt% of BCNC. Furthermore, the elastic modulus was found to increase from 2 GPa to 3.4 GPa. The BCNC obtained through cellulose treatment under controlled conditions were associated with several desirable properties and appear to be superior over the conventional methods of nanocrystals production. The enzymatic method followed in this study is expected to contribute the fabrication of high performance polymer nanocomposites in a much greener and innovative manner.     

Preparation and characterization of wheat straw fibers for reinforcing application in injection molded thermoplastic composites

The potential of wheat straw fibers prepared by mechanical and chemical processes as reinforcing additives for thermoplastics was investigated. Fibers prepared by mechanical and chemical processes were characterized with respect to their chemical composition, morphology, and physical, mechanical and thermal properties. Composites of polypropylene filled with 30% wheat straw fibers were prepared and their mechanical properties were also evaluated. The fibers prepared by chemical process exhibited better mechanical, physical and thermal properties. Wheat straw fiber reinforced polypropylene composites exhibited significantly enhanced properties compared to virgin polypropylene. However, the strength properties of the composites were less for chemically prepared fiber filled composites. This was due to the poor dispersion of the fibers under the processing conditions used. These results indicate that wheat straw fibers can be used as potential reinforcing materials for making thermoplastic composites.     

Novel composite blend microbeads of sodium alginate coated with chitosan for controlled release of amoxicillin

Composite blend microbeads of sodium alginate (NaAlg) with sodium carboxymethyl cellulose (NaCMC) containing magnesium aluminum silicate (MAS) particles and enteric coated with chitosan have been prepared to achieve controlled release (CR) of amoxicillin in stomach environment. The composite beads have been characterized by X-ray diffraction (XRD) to study drug distribution, DSC for understanding thermal stability and Fourier transform infrared (FTIR) spectroscopy to investigate chemical interactions as well as to assess the structure of the drug-loaded formulations. Surface morphology of the beads was investigated by scanning electron microscopy (SEM). The size distribution of beads loaded with drug as studied by particle size analyzer was in the range of 745-889 μm. The beads exhibited quite widely varying encapsulation efficiencies from 52 to 92%. Equilibrium swelling of the beads measured in water and in vitro release of amoxicillin in pH 1.2 medium suggests that drug release depends on polymer blend composition, concentration of MAS and extent of enteric coating.     

Impedance studies of a nano-structured conducting polymer and its application to the design of reliable scaffolds for impedimetric biosensors

Electrochemical impedance spectroscopy (EIS) as a powerful, non-invasive and informative technique was used to obtain important information about kinetics of doping process in conducting polymers. Polypyrrole (PPy) and its derivatives can form conducting polymer films which represent excellent charge transfer behaviors during doping processes. It can also have a wide range of applications in bioelectrochemistry. In the present study the conducting polymer of alpha-carboxy pyrrole (alpha-COOH-PPy), appended onto the underlying film of PPy, was prepared by electrochemical methods and its behavior was analyzed using EIS. From highly accurate fitting of impedance results it was found that the charging mechanism is governed by the diffusion process. In addition, the impedance analyses provided values for the bulk polymer parameters including diffusion coefficient (D), equilibrium capacitance (C(0)) and diffusion resistance (R(0)). The surface morphology of the polymeric film was characterized using scanning electron microscopy (SEM). The film was then used to immobilize the cytochrome C (cyt-C) and to perform its electrochemical studies. The modified cyt-C/alpha-COOH-PPy electrode was used for electrocatalytic reduction of H(2)O(2) in solution and its viability as a new impedimetric biosensor was examined. Based on the calibration curve obtained for the proposed impedimetric biosensor, the limit of detection and relative standard deviation were evaluated as 0.25mumolL(-1) and 7%, respectively. Finally, the prolonged stability test was performed and high stability and reproducibility of the new biosensor was confirmed.     

Optical, bactericidal and water repellent properties of electrospun nano-composite membranes of cellulose acetate and ZnO

In this report, ZnO nanoparticles embedded cellulose acetate (CA) fibrous membrane with multifunctional properties have been prepared through electrospinning method. The morphology of the electrospun composite membrane was analyzed by Scanning Electron Microscope (SEM). It was found that the polymer concentration in the solution has a significant effect on the morphology of the fibers. The optical property of the sample was tested using Photo Luminescence (PL) spectra. There is no significant change in the emission features of cellulose acetate with the addition of ZnO. The anti-bacterial property of the sample was studied using disc diffusion method. The wettability of the pure and composite fibrous membrane was also studied by measuring the contact angle of water on the membrane. It was observed that the embedded ZnO in the CA was responsible for the hydrophobic nature of the surface.