Low potential detection of glucose at carbon nanotube modified glassy carbon electrode with electropolymerized poly(toluidine blue O) film

A mediator glucose biosensor has been constructed by immobilizing glucose oxidase at electropolymerized poly(toluidine blue O) film on carbon nanotube modified glass carbon electrode. The toluidine blue O moieties served as redox mediators for enzymatic glucose oxidation and as polymeric network to maintain the biosensor activity. Great enhancement in current response was observed for the glucose biosensor. The detection potential could be decreased to −0.1 V (versus Ag|AgCl), where common interferences such as ascorbic acid, uric acid and acetamidophenol were not oxidized to cause interferences. The amperometric glucose biosensor offered a sensitivity of 14.5 mA M⁻¹ cm⁻² for the linear range of 1-7 mM.     

Amperometric glucose biosensor based on immobilization of glucose oxidase in electropolymerized o-aminophenol film at Prussian blue-modified platinum electrode

An amperometric glucose biosensor is developed, based on immobilization of glucose oxidase (GO_X) in an electrochemically polymerized, non-conducting poly(o-aminophenol) (POAP) film at Prussian blue (PB)-modified platinum (Pt) microelectrode. Effects of polymerization cycle number for POAP and PB, applied potential used in the determination, pH value of the detection solution and electroactive compounds on the amperometric response of the sensor were investigated and discussed. The electroactive property and rough surface of PB film result in the improvement of the detection limit and the increase of the maximum response current and sensitivity. The biosensor based on Pt/PB/POAP/GO_X electrode has two times lower detection limit, five times larger maximum current and nine times higher sensitivity than those of the biosensor based on Pt/POAP/GO_X electrode. Additionally, the biosensor shows fast response time, large response current, and good anti-interferent ability for l-ascorbic acid, uric acid and acetaminophen. Excellent reproducibility and stability of biosensor are also observed.     

Hybridization of poly(rI) with poly(rC) adsorbed to the carbon nanotube surface

Hybridization of homopolynucleotide poly(rC) adsorbed to the carbon nanotube surface with poly(rI) free in solution has been studied by absorption spectroscopy and molecular dynamics method. It was found that hybridization on the nanotube surface has a slow kinetics, the behavior of which differs essentially from fast hybridization of free polymers. The duplex obtained is characterized with the reduced thermostability and a lower hyperchromic coefficient than it was observed when the duplex was formed in the absence of the nanotube. These features point to the imperfectness in the structure of the duplex hybridized on the nanotube surface. Computer simulation showed that the strong interaction of nitrogen bases with the nanotube surface weakens significantly hybridization of two complementary oligomers, as the surface prevents the necessary conformational mobility of the polymer to be hybridized.     

Single wall carbon nanotube templated oriented crystallization of poly(vinyl alcohol)

Shearing of poly(vinyl alcohol) (PVA)/single wall carbon nanotube (SWNT) dispersions result in the formation of self-assembled oriented PVA/SWNT fibers or ribbons, while PVA solution results in the formation of unoriented fibers. Diameter/width and length of these self-assembled fibers was 5-45 μm and 0.5-3 mm, respectively. High-resolution transmission electron micrographs showed well resolved PVA (200) lattice with molecules oriented parallel to the nanotube axis. Nanotube orientation in the self-assembled fibers was also determined from Raman spectroscopy. PVA fibers exhibited about 48% crystallinity, while crystallinity in PVA/SWNT fibers was 84% as determined by wide angle X-ray diffraction. PVA and carbon nanotubes were at an angle of 25-40° to the self-assembled fiber axis. In comparison to PVA, PVA/SWNT samples exhibited significantly enhanced electron beam radiation resistance. This study shows that single wall carbon nanotubes not only nucleate polymer crystallization, but also act as a template for polymer orientation.     

Amperometric glucose biosensor based on Prussian blue-multiwall carbon nanotubes composite and hollow PtCo nanochains

In this paper, a novel glucose biosensor was developed based on immobilizing glucose oxidase (GOD) on Prussian blue-multiwall carbon nanotubes (PB@MWNTs) composite and hollow PtCo (H-PtCo) nanochains modified electrode. The PB@MWNTs/H-PtCo membrane showed good biocompatibility, large surface-to-volume ratio and excellent electron-conductive ability. The successful fabrication of the PB@MWNTs composite synthesized with MWNTs as a template and Fe(III)-reducer were characterized by UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectrometry and transmission electron microscopy (TEM). The hollow PtCo nanochains were also characterized by TEM and X-ray photoelectron spectroscopy (XPS). The response of the biosensor towards glucose under the optimized conditions, as investigated by chronoamperometry, is linear from 3.0 μM to 3.6 mM, with a low detection limit of 0.85 μM (S/N = 3) and a high sensitivity 21 mA M⁻¹ cm⁻². Moreover, the biosensor exhibits strong anti-interferent ability, good reproducibility and excellent stability.     

Amperometric glucose biosensor prepared with biocompatible material and carbon nanotube by layer-by-layer self-assembly technique

Prussian Blue (PB) based glucose biosensor was prepared by immobilizing glucose oxidase (GOD) in layer-by-layer (LBL) films with chitosan (Chi) and multi-walled carbon nanotubes (MWNTs). With the increasing of Chi/MWNTs/GOD layers, the response current to glucose was changed regularly and reached a maximum value when the number of layer was six. At the optimized condition, the biosensor exhibits excellent response performance to glucose with a linear range from 1 to 7 mM and a low detection limit of 0.05 mM. The biosensor also shows a high sensitivity of 8.017 μA mM⁻¹ cm⁻², which is attributed to the biocompatible nature of the LBL films. Furthermore, the biosensor shows rapid response, good reproducibility, long-term stability and freedom of interference from other co-existing electroactive species such as ascorbic acid and acetaminophen.     

Amperometric glucose biosensor with high sensitivity based on self-assembled Prussian Blue modified electrode

A glucose biosensor, which was based on self-assembled Prussian Blue (PB) modified electrode with glucose oxidase (GOD) immobilized in cross-linked glutaraldehyde matrix, was developed. Fourier-transform infrared spectroscopy shows that the immobilized GOD retains its native conformation. Cyclic voltammetry was used to examine the electrocatalytic property of the enzyme electrode. The prepared glucose biosensor exhibits fast response (<4 s) and low detection limit of 5 × 10⁻⁶ M. The calculated apparent Michaelis constant K_M was 6.3 ± 1.2 mM, indicating a high affinity between the GOD and glucose. The effects of glutaraldehyde concentration and GOD loading on the sensitivity of the glucose biosensor have also been investigated. Under the optimal conditions, the biosensor shows a high sensitivity of about 80 mA M⁻¹ cm⁻² in a concentration range up to 1 × 10⁻³ M. The relative standard deviation (RSD) for intra-electrode and inter-electrode were 4% and 5%, respectively. In addition, the anti-interferent ability and stability of the biosensor were also discussed.     

Rheology and properties of melt-processed poly(ether ether ketone)/multi-wall carbon nanotube composites

Poly(ether ether ketone) (PEEK)/multi-wall carbon nanotube (MWNT) composites containing up to 17 wt% filler were prepared using a twin screw extruder. Transmission electron microscopy (TEM) images reveal that the MWNTs were homogeneously dispersed in the PEEK matrix. Linear viscoelastic measurements show that both complex viscosity and moduli increase with increasing MWNT concentration. The storage modulus, G^′ exhibits a dramatic seven order increase in magnitude around 1 wt%, leading to a solid-like low-frequency behaviour at higher loadings; the effect can be attributed to network formation at a rheological percolation threshold. Rheotens measurements show that the melt strength also increases significantly on addition of nanotubes, however, the drawability decreases. An analytical Wagner model was used to calculate the apparent elongational viscosity over a wide range of elongational rates, and to reveal significant increases on addition of MWNTs, with a similar threshold behaviour. The electrical response is also dominated by percolation effects, increasing by nearly 10 orders of magnitude from 10⁻¹¹ to 10⁻¹ S/cm, on the addition of only 2 wt% MWNTs. In contrast, the thermal conductivity and tensile elastic modulus of the composites increased linearly with nanotube content, rising by 130% and 50%, at 17 wt% MWNTs, respectively.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.     

An ECL biosensor for glucose based on carbon-nanotube/Nafion film modified glass carbon electrode

Glucose oxidase was encapsulated in carbon-nanotube/Nafion film modified glass carbon electrode and was used as electrochemiluminescence (ECL) biosensor for glucose. The glucose oxidase can be fixed firmly in the Nafion film and carbon nanotubes offer excellent electrocatalytic activity toward luminol and hydrogen peroxide liberated in enzymatic reaction between glucose oxidase and glucose, which would enable sensitive determination of glucose. Under the optimum condition, the linear response range of glucose was found to be 5.0 × 10⁻⁶ to 8.0 × 10⁻⁴ mol/L, and the detection limit (defined as the concentration that could be detected at the signal-to-noise ratio of 3) was 2.0 × 10⁻⁶ mol/L. The present carbon-nanotube/Nafion biocomposite glucose oxidase ECL biosensor showed excellent properties for sensitive determination for glucose with good reproducibility and stability, and it has been used to determine the glucose concentrations in real serum samples with the satisfactory results.     

Poly(lactic acid)/carbon nanotube nanocomposites with integrated degradation sensing

For the first time, an in-situ degradation monitoring system for biodegradable polymers is reported in present work. The proposed concept is based on a conductive biodegradable polymer composite, where carbon nanotubes (CNTs) are incorporated in poly(lactic acid) (PLA) in order to develop an intelligent biocomposite system that can sense biodegradation. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of the biopolymer. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, with resistivity changes of about four orders of magnitude with biodegradation. In contrast to many other stimuli, biodegradation resulted in a reduction in resistivity due to an increased CNT network density after partial removal of the amorphous phase of the polymer matrix.     

Amperometric biosensor for ethanol based on co-immobilization of alcohol dehydrogenase and Meldola's Blue on multi-wall carbon nanotube

In this work, multi-wall carbon nanotube (MWCT) is evaluated as transducer, stabilizer and immobilization matrix for the construction of amperometric biosensor based on alcohol dehydrogenase (ADH) and Meldola's Blue (MB). The amperometric response was based on the electro catalytic properties of MB to oxidize NADH, which was generated in the enzymatic reaction of ethanol with NAD⁺ under catalysis of ADH. It is shown that the employed materials are promising as electrochemical mediators and enzyme stabilizers. The enzyme was immobilized onto the MWCT adsorbed with MB by cross-linking with glutaraldehyde. The dependence on the biosensor response for ethanol was investigated in terms of pH, supporting electrolyte, ADH and NAD⁺ amounts and working potential. The amperometric response for alcohol using this biosensor showed excellent sensitivity (4.75 μA cm⁻² mmol L⁻¹), operational stability (around 95% of the activity was maintained after 300 determinations) and wide linear response range (0.05-10 mmol L⁻¹). These favorable characteristics allowed its application for measurements of ethanol in a great variety of alcoholic beverages with a simple dilution. The precision and recovery data showed by the proposed biosensor may give reliable results for real complex matrices.     

A highly performing electrochemiluminescent biosensor for glucose based on a polyelectrolyte-chitosan modified electrode

A highly performing ECL glucose biosensor was developed by immobilizing glucose oxidase (GOD) onto a membrane modified glassy carbon electrode, which was prepared by using poly(diallyldimethylammonium chloride) (PDDA) doped with chitosan. In order to obtain the optimal performance of the ECL biosensor, the composition of modified membranes and a series of measurement conditions were investigated. Under the optimal conditions, this ECL biosensor was able to detect glucose in the range of 0.5-4.0 × 10⁴ nM with a detection limit of 0.1 nM (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The relative standard deviation was 0.99% for 5 × 10⁻⁸ mol/L glucose in repetitive measurements in the primary 12 potential cycles. This ECL biosensor offered the effectively improved stability of the electron transfer mediator and exhibited excellent properties for the ultrasensitive and selective determination of glucose with good reproducibility and stability. The present biosensor has also been used to determine the glucose concentrations in real serum samples. The recovery value for the assay of glucose ranged from 96.2 to 107% in the serum samples. The present biosensor displayed both specificity for glucose and retention of signal response even in a complex environment. Therefore, it provided an approach to the sensitive determination of glucose.     

Synthesis and electrochemical capacitance of core-shell poly (3,4-ethylenedioxythiophene)/poly (sodium 4-styrenesulfonate)-modified multiwalled carbon nanotube nanocomposites

A noncovalent method was used to functionalize multiwalled carbon nanotubes with poly (sodium 4-styrene sulfonate). And then, the core-shell poly (3,4-ethylenedioxythiophene)/functionalized multiwalled carbon nanotubes (PEDOT/PSS-CNTs) nanocomposite was successfully realized via in situ polymerization under the hydrothermal condition. In the process, PSS served for not only solubilizing and dispersing CNTs well into an aqueous solution, but also tethering EDOT monomer onto the surface of CNTs to facilitate the formation of a uniform PEDOT coating. Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to characterize the resultant PEDOT/PSS-CNTs. In addition, the PEDOT/PSS-CNTs nanocomposite (50 wt.% PEDOT) had a specific capacitance (SC) of 198.2 F g⁻¹ at a current density of 0.5 A g⁻¹ and a capacitance degradation of 26.9% after 2000 cycles, much better than those of pristine PEDOT and PEDOT/CNTs (50 wt.% PEDOT). The enhanced electrochemical performance of the PEDOT/PSS-CNTs nanocomposite (50 wt.% PEDOT) should be attributed to the high uniform system of the nanocomposite, resulting in the large surface easily contacted by abundant electrolyte ions through the three-dimensional conducting matrix.     

Processing, structure and properties of poly(ether ketone) grafted few wall carbon nanotube composite fibers

Poly(ether ketone) (PEK) was grafted onto few wall carbon nanotube (FWNT) using in-situ polymerization of 4-phenoxybenzoic acid (4-PBA) in poly(phosphoric acid) (PPA), and fibers were processed using dry-jet wet-spinning. The PEK/FWNT weight ratio was in the range of 99/1 to 80/20. The fibers have been characterized for their morphology, structure, mechanical properties, as well as electrical conductivity. The toughness (work of rupture) of the PEK fibers, as measured from the area under the stress-strain curves, was as high as 130 J/g and often exceeded the toughness of the toughest synthetic fibers such as Kevlar™ (∼45 J/g) and Zylon™ (∼50 J/g) and approached values closer to that of spider silk (∼170 J/g). PEK and PEK-g-FWNT fibers exhibit good thermal stability with degradation onset of above 500 °C under nitrogen environment, and possess high char yield (∼50% for 5 wt% FWNT containing PEK fiber). PEK-g-FWNT fibers can be processed that exhibit good dimensional stability up to 300 °C (coefficient of thermal expansion ∼−1.2 × 10⁻⁵/°C) and the axial electrical conductivity was as high as 240 S/m at 20 wt% FWNT loading.     

Structure-property behavior of poly(dimethylsiloxane) based segmented polyurea copolymers modified with poly(propylene oxide)

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure-property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10-35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.     

In situ synthesis and characterization of poly(2,5-benzoxazole)/multiwalled carbon nanotubes composites

This article reports the synthesis of poly(2,5-benzoxazole)/multiwalled carbon nanotubes (ABPBO/MWNT) composites by in situ polycondensation and their chemical and physical properties. The functional groups yielded from the surface modification of MWNTs by hydrochloric acids have been demonstrated to participate in the polymerization and thus led to the composites with homogenous dispersion of carbon nanotubes. The chemical structures and morphology of the afforded polymer composites have been fully characterized by FTIR, WAXD, UV-vis, TGA and SEM. The ABPBO/MWNT composites exhibit excellent thermal stability and greatly improved mechanical properties. The tensile modulus and tensile strength of the composites are 47% and 83%, respectively, higher than those of the polymer matrix. The dielectric constant of the composites is also significantly enhanced from 4 of the polymer matrix to 65 with the incorporation of 5 wt% MWNTs.     

聚对氨基苯磺酸/石墨烯复合膜修饰玻碳电极测定葡萄糖

制备了对氨基苯磺酸/石墨烯复合膜修饰电极,研究了葡萄糖在该修饰电极上的电化学行为.在0.1 moL/L NaOH溶液中,峰电流与葡萄糖的浓度在1 ×1O-6 ～5 ×1O-4 mol/L的范围内呈良好的线性关系,检出限为2×10-7 mol/L(S/N =3).实验结果表明对氨基苯磺酸/石墨烯复合膜显著提高了方法的检测...     

Development of electrochemical oxidase biosensors based on carbon nanotube-modified carbon film electrodes for glucose and ethanol

Functionalised multi-walled carbon nanotubes (MWCNTs) were cast on glassy carbon (GC) and carbon film electrodes (CFE), and were characterised electrochemically and applied in a glucose-oxidase-based biosensor. MWCNT-modified carbon film electrodes were then used to develop an alcohol oxidase (AlcOx) biosensor, in which AlcOx-BSA was cross-linked with glutaraldehyde and attached by drop-coating. The experimental conditions, applied potential and pH, for ethanol monitoring were optimised, and ethanol was determined amperometrically at −0.3 V vs. SCE at pH 7.5. Electrocatalytic effects of MWCNT were observed with respect to unmodified carbon film electrodes. The sensitivity obtained was 20 times higher at carbon film/MWCNT-based biosensors than without MWCNT.     

Preparation and characterisation of poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene)/poly(neutral red) modified carbon film electrodes, and application as sensors for hydrogen peroxide

Poly(3,4-ethylenedioxythiophene) (PEDOT) films have been prepared for the first time on carbon-film electrodes (CFE) in aqueous solution using electropolymerisation by potential cycling, potentiostatically and galavanostatically. Characterisation of the modified electrodes was done by cyclic voltammetry and electrochemical impedance spectroscopy and the stability of the polymer films was probed. The coated electrodes were tested for application as hydrogen peroxide sensors, by oxidation and reduction. A novel polymer film was also formed by modification of CFE by co-electropolymerisation of EDOT and the phenazine dye neutral red (NR) – (PEDOT/PNR) with a view to enhancing the properties for sensor applications. It was found that hydrogen peroxide reduction at the PEDOT/PNR coated electrodes could be carried out at a less negative potential, the sensor performance comparing very favourably with that of other polymer-modified electrodes reported in the literature.