Biofunctionalization of Multiwalled Carbon Nanotubes by Electropolymerized Poly(pyrrole‐concanavalin A) Films

The synthesis and electropolymerization of a pyrrolic concanavalin A derivative (pyrrole‐Con A) onto a multiwalled carbon nanotube (MWCNT) deposit is reported. Glucose oxidase was then immobilized onto the MWCNT‐poly(pyrrole‐Con A) coating by affinity carbohydrate interactions with the polymerized Con A protein. The resulting enzyme electrode was applied to the amperometric detection of glucose exhibiting a high sensitivity of 36 mA cm^?2 mol^?1 L and a maximum current density of 350 μA cm^?2.     

Polypyrrole/multiwalled carbon nanotubes‐based biosensor for cholesterol estimation

The nanocomposite electrode comprising of polypyrrole (PPY) and carboxy functionalized multiwalled carbon nanotubes (MWCNT) has been electrochemically fabricated onto indium–tin–oxide (ITO) electrode using p‐toluene sulfonic acid (PTS). Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been immobilized onto this PPY– MWCNT/ITO nanocomposite electrode using N‐ethyl‐N‐(3‐dimethylaminopropyl) carbodiimide and N‐hydroxy succinimide chemistry for estimation of esterified cholesterol. The ChEt–ChOx/PPY–MWCNT/PTS/ITO bioelectrode has been characterized using Fourier transform infrared spectroscopy, electrochemical techniques, and scanning electron microscope. This ChEt–ChOx/PPY–MWCNT/PTS/ITO nanobioelectrode has a response time of about 9 s, linearity of 4 × 10^?4 to 6.5 × 10^?3 M/l of cholesterol oleate concentration, K_m of 0.02 mM, and thermal stability of upto 45°C. This electrode exhibits improved biosensing characteristics compared with other total cholesterol electrodes reported in literature till date and can be used to estimate cholesterol in blood serum samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemical Capacitive Behaviour of Multiwalled Carbon Nanotubes Modified with Electropolymeric Films of Nickel Tetraaminophthalocyanine

Electrochemical capacitive behaviour of the electropolymeric nickel tetra‐aminophthalocyanine (poly‐NiTAPc) supported on multiwalled carbon nanotube (MWCNT) platform is described. From the data in 1 M H₂SO₄, the MWCNT‐poly‐NiTAPc exhibited superior capacitance (112 mF cm^?2 or 777 F g^?1). The supercapacitance of the MWCNT‐polyNiTAPc was found to be much better in 1 M H₂SO₄ than in 1 M NaOH medium. Impedance data proved that most of the stored energy of the MWCNT‐poly‐NiTAPc could be accessible at high frequency (1.6 kHz). The electrode is capable of undergoing continuous charge‐discharge process for more than a 1000 cycles without any significant deterioration in the stability.     

Nanostructured Cobalt(II) Tetracarboxyphthalocyanine Complex Supported Within the MWCNT Frameworks: Electron Transport and Charge Storage Capabilities

The electrochemical redox properties of a surface‐confined thin solid film of nanostructured cobalt(II) tetracarboxyphthalocyanine integrated with multiwalled carbon nanotube (nanoCoTCPc/MWCNT) have been investigated. This novel nanoCoTCPc/MWCNT material was characterized using SEM, TEM, zeta analysis and electrochemical methods. The nanoCoTCPc/MWCNT nanohybrid material exhibited an extra‐ordinarily high conductivity (15 mS cm^?1), which is more than an order of magnitude greater than that of the MWCNT‐SO₃H (527 µS cm^?1) and three orders of a magnitude greater than the nanoCoTCPc (4.33 µS cm^?1). The heterogeneous electron transfer rate constant decreases as follows: nanoCoTCPc/MWCNT (k_app≈19.73×10^?3 cm s^?1)>MWCNT‐SO₃H (k_app≈11.63×10^?3 cm s^?1)>nanoCoTCPc (k_app≈1.09×10^?3 cm s^?1). The energy‐storage capability was typical of pseudocapacitive behaviour; at a current density of 10 µA cm^?2, the pseudocapacitance decreases as nanoCoTCPc/MWCNT (3.71×10^?4 F cm^?2)>nanoCoTCPc (2.57×10^?4 F cm^?2)>MWCNT‐SO₃H (2.28×10^?4 F cm^?2). The new nanoCoTCPc/MWCNT nanohybrid material promises to serve as a potential material for the fabrication of thin film electrocatalysts or energy‐storage devices.     

Spatial Architecture of Modified Carbon Nanotubes/Electrochemically Reduced Graphene Oxide Nanomaterial for Fast Electron Transfer. Application in Glucose Biosensor

Electron transfer (ET) reactions in bioelectrocatalysis of enzymes at electrode surfaces require not only the efficient immobilization, but also highly conductive nanostructured platform, which allows for retaining its bioactivity and structural conformation. The novel architecture of spatially separated electrochemically reduced graphene oxide (ERGO) by multi‐walled carbon nanotubes functionalized with 4‐(pyrrole‐1‐yl) benzoic acid (MWCNT/PyBA) with the accurate porous structure could be an alternative for earlier approaches to the construction of bioelectrocatalytic systems with rapid diffusion of reagents from the solution to the enzyme molecule. The formation of ERGO/MWCNT/PyBA system was confirmed by electrochemical, spectroscopic and microscopic methods. The cyclic voltammetry experiments revealed that the presence of ERGO in the conductive material affects the electronic communication between the enzyme molecule and modified electrode surface greatly improving its ET properties resulting in a double increase of the heterogeneous ET rate constant value (k_s=6.5 s^?1). The fabricated glucose oxidase based biosensor sensitively detects glucose, therefore, ERGO/MWCNT/PyBA architecture could provide a novel and efficient platform for immobilization of redox enzymes.     

Bioelectrochemical response of the polyaniline galactose oxidase electrode

Galactose oxidase has been immobilized in a polyaniline film. The response current of the galactose oxidase electrode is a function of the applied potential and increases as the pH increases from 5.61 to 7.25. The optimum pH of the immobilized galactose oxidase is 7.25. The activation energy of the enzyme-catalysed reaction is 41.8 kJ mol⁻¹. The response current of the enzyme electrode shows good reproducibility at temperatures below the optimum temperature of 30.4°C and increases as the galactose concentration increases from 0.2 to 6 mmol dm⁻³. Thus the polyaniline galactose oxidase electrode can be used to determine galactose concentration.     

Preparation and morphological,electrical, and mechanical properties of polyimide‐grafted MWCNT/polyimide composite

Precursor of polyimide, polyamic acid has been prepared sucessfully. Acid‐modified carbon nanotube (MWCNT) was grafted with soluble polyimide then was added to the polyamic acid and heated to 300 °C to form polyimide/carbon nanotube composite via imidation. Morphology, mechanical properties and electrical resistivity of the MWCNT/polyimide composites have been studied. Transmission electron microscope microphotographs show that the diameter of soluble polyimide‐grafted MWCNT was increased from 30–60 nm to 200 nm, that is a thickness of 70–85 nm of the soluble polyimide was grafted on the MWCNT surface. PI‐g‐MWCNT was well dispersed in the polymer matrix. Percolation threshold of MWCNT/polyimide composites has been investigated. PI‐g‐MWCNT/PI composites exhibit lower electrical resistivity than that of the acid‐modified MWCNT/PI composites. The surface resistivity of 5.0 phr MWCNT/polyimide composites was 2.82 × 10⁸ Ω/cm² (PI‐g‐MWCNT) and 2.53 × 10⁹ Ω/cm² (acid‐modified MWCNT). The volume resistivity of 5.0 phr MWCNT/polyimide composites was 8.77 × 10⁶ Ω cm (PI‐g‐MWCNT) and 1.33 × 10¹³ Ω cm (acid‐modified MWCNT).Tensile strength and Young's modulus increased significantly with the increase of MWCNT content. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3349–3358, 2007     

Synthesis and Cytotoxic Activity of Macromolecular Prodrug of Cisplatin Using Poly(ethylene glycol) with Galactose Residues or Antennary Galactose Units

To provide a macromolecular prodrug with recognition ability for hepatoma cells, we synthesized new conjugates of cisplatin (CDDP) and poly(ethylene glycol) (PEG) with galactose residues or antennary galactose units (Gal4A, four branched galactose residues) at the chain terminus, Gal‐PEG‐DA/CDDP or Gal4A‐PEG‐DA/CDDP conjugates. An antennary (branched) structure of Gal4A was designed based on the fact that saccharide clusters with branched structures show highly effective binding with saccharide receptors, a phenomenon known as the ‘cluster effect’. The cytotoxic activity of the conjugates was investigated against HepG2 human hepatoma cells in vitro and compared with a control conjugate without galactose, MeO‐PEG‐DA/CDDP. Gal‐PEG‐DA/CDDP and Gal4A‐PEG‐DA/CDDP conjugates showed lower IC₅₀ values (3.1×10^–4 and 2.3×10^–4 M , respectively) than the MeO‐PEG‐DA/CDDP conjugate (10.5×10^–4 M ). The cytotoxic activities of these conjugates with galactose residues or antennary galactose units were inhibited as a result of the addition of galactose and strongly inhibited by the addition of Gal4A, however the inclusion of a methoxy group (the MeO‐PEG‐DA/CDDP conjugate) did not affect the activity. These results suggest that the Gal4A unit introduced to the conjugate has effective recognition ability against HepG2 human hepatoma cells.     

Preparation and Electrochemical Characterization of an Enzyme Electrode Based on Catalase Immobilized onto a Multiwall Carbon Nanotube‐Thionine Film

The present study was aimed at investigating the use of a mixture multiwall carbon nanotube (MWCNT) and thionine (Th) dye in designing of a thionine‐based electrochemical biosensor containing catalase (Ct) enzyme (MWCNT‐Nafion‐Th/Ct) onto a glassy carbon electrode (GCE). The effects of pH, MWCNT concentration and thionine concentration on electrochemical response were explored for optimum analytical performance. The modified electrode exhibited a pair of well‐defined, quasi‐reversible peaks at formal potential (E^o′) = ‐0.218 ± 0.017 V vs. Ag/AgCl corresponding to the Th_ox/Th_red redox couples in the presence of MWCNT, Nafion, and Ct. The electrochemical parameters, including charge‐transfer coefficient (0.36), and apparent heterogeneous electron transfer rate constant (4.28 ± 0.26 s^?1) were determined. Using differential pulse voltammetry, the prepared enzyme electrode exhibited a linear response to hydrogen peroxide (H₂O₂) in the range of 10.0‐100.0 μM with a detection limit 8.7 μM and a sensitivity of 6051.0 μA mM^?1 cm^?2.     

Avidin and Glucose Oxidase‐non‐covalently Functionalized Multi‐walled Carbon Nanotubes: A New Analytical Tool for Building a Bienzymatic Glucose Biosensor

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL^?1 MWCNTs in a solution of 2.00 mg mL^?1 GOx+1.00 mg mL^?1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at ?0.100 V in the presence of 5.0×10^?4 M hydroquinone, was (4.8±0.3) μA mM^?1 (r²=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk.     

Molecular motion,morphology, and thermal properties of multiwall carbon nanotube/polysilsesquioxane composite

Diglycidyl ether of bisphenol A (DGEBA)‐bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with 3‐aminopropyltriethoxysilane. Acid‐modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A‐bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A‐bridged polysilsesquioxane (MWCNT/DGEBA‐PSSQ) composites. The molecular motion of MWCNT/DGEBA‐PSSQ nanocomposites was studied by high‐resolution solid‐state ¹³C NMR. Acid‐modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA‐PSSQ decreased with acid‐modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA‐PSSQ was increased. SEM and TEM microphotographs confirm that acid‐modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA‐PSSQ. The dynamic mechanical properties of acid‐modified MWCNT/DGBEA‐PSSQ composites are more favorable than those of unmodified MWCNT. T_g of the DGEBA‐PSSQ decreased from 174.0 °C (neat DGEBA‐PSSQ) to 159.0 °C (1 wt % unmodified MWCNT) and 156.0 °C (1 wt % acid‐modified MWCNT). The storage modulus (at 30 °C) of the DGEBA‐PSSQ increased from 1.23 × 10⁹ Pa (neat DGEBA‐PSSQ) to 1.65 × 10⁹ Pa (1 wt % acid‐modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA‐PSSQ decreased to 6.88 × 10⁸ Pa (1 wt % unmodified MWCNT). At high temperature, above 150 °C, storage modulus of nanocomposites was higher than that of neat polymer system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 472–482, 2008     

Glucose Biosensor Based on Multi‐Walled Carbon Nanotube Modified Glassy Carbon Electrode

An amperometric glucose biosensor based on multi‐walled carbon nanotube (MWCNT) modified glassy carbon electrode has been developed. MWCNT‐modified glassy carbon electrode was obtained by casting the electrode surface with multi‐walled carbon nanotube materials. Glucose oxidase was co‐immobilized on the MWCNT‐modified glassy carbon surface by electrochemical deposition of poly(o‐phenylenediamine) film. Enhanced catalytic electroreduction behavior of oxygen at MWCNT‐modified electrode surface was observed at a potential of ?0.40 V (vs. Ag|AgCl) in neutral medium. The steady‐state amperometric response to glucose was determined at a selected potential of ?0.30 V by means of the reduction of dissolved oxygen consumed by the enzymatic reaction. Common interferents such as ascorbic acid, 4‐acetamidophenol, and uric acid did not interfere in the glucose determination. The linear range for glucose determination extended to 2.0 mM and the detection limit was estimated to be about 0.03 mM.     

Voltammetric Determination of Phenoxybenzyl‐Type Insecticides at Chemically Modified Conducting Polymer‐Carbon Nanotubes Coated Electrodes

The electrochemical reduction of three common insecticides such as cypermethrin (CYP), deltamethrin (DEL) and fenvalerate (FEN) was investigated at glassy carbon electrode (GCE), multiwalled carbon nanotubes modified GCE (MWCNT‐GCE), polyaniline (herein called as modifier M₁) and polypyrrole (herein called as modifier M₂) deposited MWCNT/GCE using cyclic voltammetry. Influences of pH, scan rate, and concentration were studied. The surface morphology of the modified film was characterized by scanning electron microscopy (SEM) and X‐ray diffraction analysis (XRD). A systematic study of the experimental parameters that affect differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived at. The calibration plots were linear over the insecticide's concentration range 0.1–100 mg L^?1 and 0.05–100 mg L^?1 for all the three insecticides at MWCNT‐GCE and MWCNT(M₁)‐GCE respectively. The MWCNT(M₂)‐GCE performed well among the three electrode systems and the determination range obtained was 0.01–100 mg L^?1 for CYP, DEL and FEN. The limit of detection (LOD) was 0.35 μg L^?1, 0.9 μg L^?1 and 0.1 μg L^?1 for CYP, DEL and FEN respectively on MWCNT(M₂)‐GCE modified system. Suitability of this method for the trace determination of insecticide in spiked soil sample was also determined.     

An Amperometric Biological Toxic Hydrazine Sensor Based on Multiwalled Carbon Nanotubes and Iron Tetrasulfonated Phthalocyanine Composite Modified Electrode

Hydrazines are well‐known for their diverse biological properties but especially for their toxicity. An amperometric hydrazine sensor was developed at multi‐walled carbon nanotubes (MWCNT) and iron tetrasulfonated phthalocyanine (FeTsPc) composite modified electrode for the first time. The TEM and UV‐Vis spectroscopy results revealed the successful formation of MWCNT/FeTsPc composite. Compared with the response of MWCNT and FeTsPc modified electrodes, the MWCNT/FeTsPc composite showed enhanced oxidation current response with lower overpotential for hydrazine. Under optimum conditions, the amperometric i–t response of hydrazine was linear in the concentration range from 100 nM L^?1 to 3 μM L^?1 with the detection limit of 7.6 nM L^?1. The response time of hydrazine was found as 6 s with a high sensitivity of 7.615 μA/μM L^?1 cm^?2.     

Synthesis and studies of thermal,mechanical and electrical properties of MWCNT–cyclodextrin as a nanoparticle in polyamide matrix based on 2,2‐Bis[4‐(4‐aminophenoxy)phenyl] propane

In the present research, polyamide (PA) ( 6 ) was synthesized by the polycondensation reaction of 2,2‐Bis[4‐(4‐aminophenoxy)phenyl] propane as a diamine ( 4 ) with adipic acid ( 5 ) in the optimized condition. The resulting PA was characterized using Fourier transform infrared spectroscopy, Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy, inherent viscosity (η_inh), X‐ray diffraction, and solubility tests. Also, the thermal property of the new PA ( 6 ) was investigated by using Thermogravimetric analysis. To apply multiwall carbon nanotube (MWCNT) as an effective reinforcement in polymer composites, it is essential to have appropriate proper dispersion, interfacial adhesion between the MWCNT and polymer matrix, and increasing solubility. With this end particularly, functionalized MWCNTs were combined with a soluble molecule, and a series of modified MWCNT with cyclodextrin (Cy) known as PA/MWCNT‐Cy composite film (2, 5, and 8 wt%) were prepared by a solution intercalation technique. Field emission scanning electron microscopy images showed that MWCNT‐Cy was well dispersed in the PA matrix. Thermogravimetric analysis indicated an increase in thermal stability of nanocomposites as compared with the pristine PA. Anisotropic structure of the synthesized films and dispersed MWCNT‐Cy in the films approved by use of X‐ray diffraction and field emission scanning electron microscopy. The resultant PA/MWCNT‐Cy composite films were electrically conductive, which is favorable for many practical uses. Measurements of mechanical properties of these composite films showed high strength in 8% MWCNT‐Cy content. Also, results showed increases in Young's modulus and tensile strength. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of a Molecularly Imprinted Poly(Acrylic Acid)‐MWCNT Nanocomposite Electrochemical Sensor for Tramadol Determination in Pharmaceutical Samples

A new voltammetric sensor based on molecularly imprinted poly(acrylic acid)‐MWCNT nanocomposite (MIP‐MWCNT) drop‐coated onto glassy carbon electrode (GCE) was developed and applied to tramadol (TR) determination in pharmaceutical samples. The voltammetric sensor prepared by suspension of MIP‐MWCNT at 1 : 1 (w/w) ratio show an improved performance compared to unmodified GCE. The electrochemical method is based on preconcentration of tramadol onto MIP‐MWCNT modified GCE surface at ?1.5 V vs Ag/AgCl for 180 s in 0.1 Britton‐Robinson buffer (pH 8.0) at stirred solution. Upon preconcentration, the differential anodic voltammogram was recorded under the optimized condition giving rise to an analytical curve varying from 9.0 up to 30.0 μmol L^?1 (R²=0.997) and limits of detection and quantification of 1.4 and 4.8 μmol L^?1, respectively. The method precision was assessed in terms of intraday (n=6) and interday (two consecutive days) precision, giving relative standard deviations (RSD%) values between 2.8 to 7.4 %. Excipients usually found in pharmaceutical pills (magnesium stearate, microcrystalline cellulose, starch, and silica) and paracetamol were evaluated as potential interferents, however no interference was evidenced in TR determination. The method applicability was evaluated by TR analysis in pharmaceutical samples. Moreover, the method accuracy was attested by comparison of addition and recovery assays with a reference technique (high‐performance liquid chromatography).     

Synthesis of metal (Fe or Pd)/alloy (Fe–Pd)‐nanoparticles‐embedded multiwall carbon nanotube/sulfonated polyaniline composites by γ irradiation

Composites of multiwall carbon nanotubes (MWCNTs) and sulfonated polyaniline (SPAN) were prepared through the oxidative polymerization of a mixture of aniline, 2,5‐diaminobenzene sulfonic acid, and MWCNTs. Fe, Pd, or Fe–Pd alloy nanoparticles were embedded into the MWCNT–SPAN matrix by the reduction of Fe, Pd, or a mixture of Fe and Pd ions with γ radiation. Sulfonic acid groups and the emeraldine form of backbone units in SPAN served as the source for the reduction of the metal ions in the presence of γ radiation. The existence of metallic/alloy particles in the MWCNT–SPAN matrix was further ascertained through characterization by high‐resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, and conductivity measurements. HRTEM pictures clearly revealed the existence of Fe, Pd, and Fe–Pd nanoparticles of various sizes in the MWCNT–SPAN matrices. There were changes in the electronic properties of the MWCNT–SPAN–M composites due to the interaction between the metal nanoparticles and MWCNT–SPAN. Metal‐nanoparticle‐loaded MWCNT–SPAN composites (MWCNT–SPAN–M; M = Fe, Pd, or Fe–Pd alloy) showed better thermal stability than the pristine polymers. The conductivity of the MWCNT–SPAN–M composites was approximately 1.5 S cm^?1, which was much higher than that of SPAN (2.46 × 10^?4 S cm^?1). Metal/alloy‐nanoparticle‐embedded, MWCNT‐based composite materials are expected to find applications in molecular electronics and other fields. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3355–3364, 2006     

Filling Carbon Nanotubes with Prussian Blue Nanoparticles of High Peroxidase‐Like Catalytic Activity for Colorimetric Chemo‐ and Biosensing

Facile filling of multiwalled carbon nanotubes (MWCNTs) with Prussian blue nanoparticles (PBNPs) of high peroxidase‐like catalytic activity was performed to develop novel colorimetric sensing protocols for assaying H₂O₂ and glucose. Fine control of PBNP growth was achieved by modulating the concentration ratio of K₃[Fe(CN)₆] and FeSO₄ precursors in an acidic solution containing ultrasonically dispersed MWCNTs, and thus size‐matched PBNPs could be robustly immobilized in the cavities of the MWCNTs (MWCNT‐PB_in). Unlike other reported methods involving complicated procedures and rigorous preparation/separation conditions, this mild one‐pot filling method has advantages of easy isolation of final products by centrifugation, good retention of the pristine outer surface of the MWCNT shell, and satisfactory filling yield of (24±2) %. In particular, encapsulation of PBNPs of poor dispersibility and limited functionality in dispersible and multifunctional MWCNT shells creates new and valuable opportunities for quasihomogeneous‐phase applications of PB in liquid solutions. The MWCNT‐PB_in nanocomposites were exploited as a peroxidase mimic for the colorimetric assay of H₂O₂ in solution by using 3,3′,5,5′‐tetramethylbenzidine (TMB) as reporter, and they gave a linear absorbance response from 1 μM to 1.5 mM with a limit of detection (LOD) of 100 nM . Moreover, glucose oxidase (GOx) was anchored on the outer surface of MWCNT‐PB_in to form GOx/MWCNT‐PB_in bionanocomposites. The cooperation of outer‐surface biocatalysis with peroxidase‐like catalysis of interior PB resulted in a novel cooperative colorimetric biosensing mode for glucose assay. The use of GOx/MWCNT‐PB_in for colorimetric biosensing of glucose gave a linear absorbance response from 1 μM to 1.0 mM and an LOD of 200 nM . The presented protocols may be extended to other multifunctional nanocomposite systems for broad applications in catalysis and biotechnology.     

Microwave‐assisted synthesis of nanocomposites from polyimides chemically cross‐linked with functionalized carbon nanotubes for aerospace applications

Polymer‐carbon nanotube nanocomposites are extensively investigated for microelectronics and aerospace applications. In this study, novel polyimide/f‐MWCNT nanocomposites made from 2,4‐bis(4‐aminophenylamido)‐6‐chloroquinazoline, pyromellitic dianhydride and functionalized‐Multi Walled Carbon Nanotubes (f‐MWCNT) by an efficient microwave assisted method were investigated. The structure of the prepared diamine monomer was confirmed by FT‐IR, ¹H‐NMR, and ¹³C‐NMR spectral techniques. The prepared nanocomposites (T_g values from 338°C to 375°C) show improved thermal property as indicated by differential scanning calorimetry and thermogravimetric analysis. Polyimide/f‐MWCNT nanocomposites were found to have higher dielectric constant, and the limiting oxygen index values of prepared nanocomposites are in the range of 29.5 to 35.5, indicating a high flame retardancy. Additionally, the morphological studies were conducted by X‐ray diffraction and scanning electron microscopy. Overall, it is observed that chemically connected polyimide‐functionalized carbon nanotube nanocomposites could be used for aerospace and microelectronics applications that require high T_g, dielectric constant and high flame retardancy.     

Highly Sensitive Choline Oxidase Enzyme Inhibition Biosensor for Lead Ions Based on Multiwalled Carbon Nanotube Modified Glassy Carbon Electrodes

The determination of lead ions by inhibition of choline oxidase enzyme has been evaluated for the first time using an amperometric choline biosensor. Choline oxidase (ChOx) was immobilized on a glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT) through cross‐linking with glutaraldehyde. In the presence of ChOx, choline was enzymatically oxidized into betaine at –0.3 V versus Ag/AgCl reference electrode, lead ion inhibition of enzyme activity causing a decrease in the choline oxidation current. The experimental conditions were optimised regarding applied potential, buffer pH, enzyme and substrate concentration and incubation time. Under the best conditions for measurement of the lowest concentrations of lead ions, the ChOx/MWCNT/GCE gave a linear response from 0.1 to 1.0 nM Pb²⁺ and a detection limit of 0.04 nM. The inhibition of ChOx by lead ions was also studied by electrochemical impedance spectroscopy, but had a narrower linear response range and low sensitivity. The inhibition biosensor exhibited high selectivity towards lead ions and was successfully applied to their determination in tap water samples.