Copper-decorated carbon nanotubes based composite electrodes for non-enzymatic detection of glucose

ABSTRACT: The aim of this study was to prepare three types of multi-wall carbon nanotube (CNT)-based composite electrodes and to modify their surface by copper electrodeposition for non-enzymatic oxidation and determination of glucose from aqueous solution. Copper decorated multi-wall carbon nanotube composite electrode (Cu/CNT-Epoxy) exhibited the highest sensitivity to glucose determination. The reliability of the Cu/CNT-Epoxy electrode was verified by application of this composite electrode for the determination of glucose in real blood serum samples.     

Development of highly sensitive non-enzymatic sensor for the selective determination of glucose and fabrication of a working model

Copper oxide (CuO)/copper oxalate (CuOx) modified non-enzymatic electrochemical sensor for the detection of glucose in alkaline medium was fabricated by electrochemical anodisation of copper electrodes in potassium oxalate solution. Morphology of the modified copper electrode was studied by Scanning Electron Microscopy (SEM) and its electrochemical behaviour by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The formation of CuOx on the copper electrode was confirmed by the Infra-red Reflection Absorption Spectrum (IRRAS). The modified electrodes were found to be microporous and rough. Linear Sweep Voltammetry (LSV) and amperometry were adopted to investigate the direct electrocatalytic oxidation of glucose on CuO/CuOx modified electrode in alkaline medium which showed excellent catalytic activity. The best performance of the sensor was obtained at 0.7 V and in 0.1 M sodium hydroxide (NaOH). At this optimum potential, the sensor was highly selective to glucose in the presence of ascorbic acid (AA) and uric acid (UA) which are common interfering species in biological fluids. The sensitivity was found to be very high (1890 μA mM⁻¹ cm⁻²) with excellent linearity (R = 0.9999) up to 15 mM having a low detection limit of 0.05 μM (S/N = 3). The modified electrode was tested for glucose level in blood serum. Based on the optimised conditions, a working model of the sensor was made and successfully tested for glucose.     

PtRu nanoparticles supported on nitrogen-doped multiwalled carbon nanotubes as catalyst for methanol electrooxidation

Nitrogen-doped carbon nanotubes (N-CNT) obtained by plasma treatment were compared to the conventional acid-treated carbon nanotubes (O-CNT) as catalyst support for platinum-ruthenium (PtRu) nanoparticles in the anodic oxidation of methanol in direct methanol fuel cells. PtRu catalysts were prepared by an impregnation-reduction method from chloride precursors with metal loadings of 20 wt.%, and were characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical methods. Voltammetry and chronoamperometry studies showed that the performance of PtRu/N-CNT was significantly higher compared to PtRu/O-CNT and also to the commercial E-TEK PtRu/C catalyst, indicating that N-CNT are an interesting support material for fuel cell electrocatalyst. Nitrogen plasma treatment produced pyridinic and pyrrollic species on the CNT surface, which acts as the anchoring sites for the deposition of PtRu particles. A mechanism for the deposition of PtRu on N-CNT is tentatively proposed and discussed.     

Three-dimensional heterostructure of metallic nanoparticles and carbon nanotubes as potential nanofiller

ABSTRACT: The effect of the dimensionality of metallic nanoparticle-and carbon nanotube-based fillers on the mechanical properties of an acrylonitrile butadiene styrene (ABS) polymer matrix was examined. ABS composite films, reinforced with low dimensional metallic nanoparticles (MNPs, 0-D) and carbon nanotubes (CNTs, 1-D) as nanofillers, were fabricated by a combination of wet phase inversion and hot pressing. The tensile strength and elongation of the ABS composite were increased by 39% and 6%, respectively, by adding a mixture of MNPs and CNTs with a total concentration of 2 wt%. However, the tensile strength and elongation of the ABS composite were found to be significantly increased by 62% and 55%, respectively, upon addition of 3-D heterostructures with a total concentration of 2 wt%. The 3-D heterostructures were composed of multiple CNTs grown radially on the surface of MNP cores, resembling a sea urchin. The mechanical properties of the ABS/3-D heterostructured nanofiller composite films were much improved compared to those of an ABS/mixture of 0-D and 1-D nanofillers composite films at various filler concentrations. This suggests that the 3-D heterostructure of the MNPs and CNTs plays a key role as a strong reinforcing agent in supporting the polymer matrix and simultaneously serves as a discrete force-transfer medium to transfer the loaded tension throughout the polymer matrix.     

Enhanced degradation of reactive dyes using a novel carbon ceramic electrode based on copper nanoparticles and multiwall carbon nanotubes

A novel carbon ceramic electrode consisting of CuNPs and MWCNT was developed to treat reactive orange 84 (RO84) wastewater using ultrasound-assisted electrochemical degradation. The proposed electrode generated more hydroxyl radicals than non-nanoparticle electrodes did. In addition, a new electrochemical sensor was applied to determine residue RO84 in an aqueous medium during discoloration. This sensor is based on a glassy carbon electrode modified with gold nanourchins and graphene oxide and can detect RO84 concentration in the range of 1.0-1200 μmol·L^-1 with the detection limit of 0.03 μmol·L^-1. The degradation effects of the modified electrode on RO84 were evaluated systematically with different initial pH values, time durations, and amounts of CuNPs and MWCNT. The results suggested that the removal efficiency of RO84 was approximately 83% after 120 min of electrolysis in a phosphate buffer with pH 8.0 using a carbon ceramic electrode made with 4.0 wt% CuNPs and 4.0 wt% MWCNT. The possible mechanism of RO84 degradation was monitored by gas chromatography-mass spectrometry, and degradation pathways were proposed.     

Seed-mediated growth of platinum nanoparticles on carbon nanotubes for the fabrication of electrochemical biosensors

Platinum nanoparticles (PtNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped onto the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution which contains H₂PtCl₆ and ascorbic acid. PtNPs were successfully grown onto the CNT surface due to the chemical reduction of Pt(IV). The electrode modified with AuNP_seed/PtNP/CNT film displayed excellent electrochemical response to H₂O₂ at 0.45 V versus saturated calomel electrode (SCE) with sensitivity much larger than that of PtNP/CNT and AuNP_seed/PtNP modified electrodes. Glucose oxidase was selected as a model enzyme and electrodeposited onto the AuNP_seed/PtNP/CNT modified electrode in the presence of a detergent. The resulting biosensor enabled selective determination of glucose with high sensitivity of 4.49 μA mM⁻¹, quick response time about 2 s, low-detection limit of 0.5 μM and wide linear range from 1 μM to 4 mM with a correlation coefficient 0.9998. Thus, the modified electrode proved to be a nice electrochemical biosensing platform for the fabrication of oxidase-based biosensors.     

Photocatalytic properties of mesoporous TiO2 nanocomposites modified with carbon nanotubes and copper

The photocatalytic activity of mesoporous TiO₂ modified by the addition of carbon nanotubes (CNTs) and Cu is reported. Nanocomposites of carbon nanotubes (CNTs) containing varying amounts of Cu were formed by treatment with Cu²⁺ then reduced to Cu⁰ using NaBH₄ as the reducing agent. The mesoporous TiO₂, synthesized by a sol-gel method from titanium isopropoxide, was combined with the CNT/Cu nanocomposites to form the photocatalysts which were characterized by XRD, SEM, TEM, FTIR, XPS and BET surface area analysis. The photocatalytic properties of the mesoporous TiO₂ composites were studied by measuring the degradation of methyl orange (MO) which was optimal in the sample containing 20 wt% of the Cu-CNT nanocomposite. The degradation efficiency for MO was a synergistic effect of photo-degradation of TiO₂ and may be due to improvement of the electrical conductivity of the system by the presence of the CNT/Cu networks, since the photodegradation of MO and the photocatalytic activity of the photoactive systems increased with increasing copper content.     

Constructing polymer brushes on multiwalled carbon nanotubes by in situ reversible addition fragmentation chain transfer polymerization

A fascinating nanoobject, diblock polymer brushes with a hard core of multiwalled carbon nanotubes (MWNTs) and a relatively soft shell of poly(methylmethacrylate)-block-polystyrene (PMMA-b-PS), was easily constructed by in situ reversible addition fragmentation chain transfer polymerization (RAFT) of methylmethacrylate followed by styrene (St) on the modified convex surfaces of MWNTs (MWNT-PMMA). The structure and morphology of the hybrid nanomaterials were characterized by FTIR, TEM, SEM, NMR, DSC and TGA. The results showed that both styrene and acrylate type monomers can be easily initiated and then propagated on the MWNT sidewalls via the in situ RAFT approach, and the length of the PS blocks increases with increasing St:MWNT-PMMA weight feed ratio.     

Dispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions

The dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloroform and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer^® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions.     

Semi-continuous production of multiwalled carbon nanotubes using magnetic field assisted arc furnace

A high-temperature arc furnace with an applied external magnetic field has been used to grow carbon nanotubes. The magnetic field was able to spread and stabilize the plasma enabling the use of larger electrodes than could be used successfully with no magnetic field. By having a stable plasma across the entire anode surface, larger amounts of carbon black were able to be transformed into carbon nanotubes. In addition, a multiple-pronged anode was designed. The use of the pronged anode created a semi-continuous process which allowed for the amount of nanotubes produced per run to increase.     

Polyelectrolyte-functionalized multiwalled carbon nanotubes: preparation, characterization and layer-by-layer self-assembly

Two kinds of polyelectrolyte: polyacrylic acid (PAA) and poly(sodium 4-styrenesulfonate) (PSS), were grafted onto the convex surfaces of multiwalled carbon nanotubes (MWNTs) by surface-initiating ATRP (atom transfer radical polymerization) from the initiating sites previously anchored onto the convex surfaces of MWNTs. The grafted polyelectrolyte can be efficiently quantified by the feed ratio of monomer to MWNT-based macroinitiator, and the maximum amount of grafted polymer is higher than 55 wt%. The polyelectrolyte-coated MWNTs resembled core-shell structures justified by the TEM images of the samples obtained, which provided direct evidence for the covalent modification of MWNT. FTIR, ¹H NMR and TGA were used to determine the chemical structure of the resulting products. Comparison of UV-Vis spectra demonstrated that the products were water-soluble, and that PSS was more effective for improving the water solubility of carbon nanotubes. Using the polyelectrolyte- and carboxylic acid-functionalized MWNTs as templates, and poly(2-(N,N-dimethylaminoethyl) methacrylate (PDMAEMA)/hyperbranched polysulfone amine (HPSA) and PSS as polycation and polyanion, respectively, layer-by-layer (LbL) electrostatic self-assembly was conducted in order to explore the application of the functionalized nanotubes. It was found that the functionalized MWNTs have a high efficiency for loading polyelectrolytes by the LbL approach (the adsorbed polymer quantity is higher than 10 wt% in one assembling step). TEM observations showed that the assembled polymer shell on the MWNT surfaces was very even and flat.     

Functional gold nanorod particles on conducting polymer poly(3-octylthiophene) as non-enzymatic glucose sensor

The immobilization of surface-functionalized self-assembled monolayer (SAM) gold nanoparticles onto poly(3-octylthiophene) (POT) was achieved by the cooperation of hydrophobic forces. SAMs were prepared by 11-mercaptoundecanoicacid (MUA), 4-mercaptophenyl boronic acid (MPB), and 1-decanethiol (DT) hydrophobic substrates. Nanoparticles-SAM-POT system was characterized by cyclic voltammetry, SEM, EDAX and contact angle measurements. SAMs (MUA) is closely packed providing effective blocking of the underlying platinum electrode and preventing a ferrocyanide molecule from penetrating. However, potential scanning was applied at SAMs (MUA) modified electrode on which electron penetrating holes or defects were occured. Since SAMs (MPB) is poorly packed according to SAMs (MUA), ferrocyanide molecules could penetrate to SAMs (MPB) modified electrode surface. POT-Au-SAM (MPB) electrode was used for glucose determination as potentiometric non-enzymatic glucose sensor. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 5-30 mM glucose including the level of human blood glucose.     

Radiolytic introduction of multiple functional groups to multiwalled carbon nanotubes and their application as biosensor supports

Tyrosinase was immobilized on multiwalled carbon nanotube (MWNT) supports that were functionalized with multiple groups. It was then used for the detection of phenolic compounds. The radiation‐induced graft polymerization of 1‐[(4‐ethenylphenyl)methyl]‐3‐buthyl‐imidazolium chloride and vinyl ferrocene introduced functional groups derived from both species onto the nanotubes' surfaces: imidazolium salts that contained sites for the enzyme's immobilization via ionic bonding and ferrocene compounds that acted as electron transfer mediators via redox reactions. Using these additives at a 1 : 4 molar ratio resulted in an electrode with optimized current. The multifunctionalized nanotube supports were characterized by X‐ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis. The prepared tyrosinase‐immobilized biosensor showed a sensing range of 1.0 × 10^?4 M to 7.0 × 10^?4 M and was used for the detection of phenolic compounds in red wines. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Diameter control of multiwalled carbon nanotubes using experimental strategies

Multiwalled carbon nanotubes (MWNTs) were synthesized using a chemical vapor deposition floating feed method in a vertical reactor. Effects of the preparation variables on the average diameter of carbon nanotubes were systematically examined using the fractional factorial design (FFD), path of the steepest ascent, and central composite design (CCD) coupled with the response surface methodology. From the FFD study, the main and interactive effects of reaction temperature, methane flow rate, and chamber pressure were concluded to be the key factors influencing the diameter of MWNTs. Two empirical models, representing the dependence of the diameter of carbon nanotubes at the vicinities around maximum (420 nm) and minimum (15 nm) on the reaction temperature and methane flow rate, were constructed in two independent CCD studies. These models, shown as contour diagrams, indicated that the diameter of carbon nanotubes generally increased with increasing reaction temperature and methane flow rate. Based on both models, the diameter of MWNTs from 15 to 420 nm can be controlled precisely by using a continuous CVD fabrication method.     

Surface oxygen complexes as governors of neopentane sorption in multiwalled carbon nanotubes

Multiwalled carbon nanotube (MWCNT) samples were obtained by purification and ball-milling of a MWCNT sample synthesized by catalytic chemical vapor decomposition. These samples were oxidized with KMnO₄-H₂SO₄ solution. A heat treatment was employed to decompose the oxygenated groups created by the oxidation treatment. The samples were characterized by transmission electron microscopy (TEM), adsorption of nitrogen, pore size distribution, and by thermogravimetric analysis combined with mass spectroscopy (TG-MS). The dynamics of 2,2-dimethyl-propane (neopentane) sorption was studied by frequency-response (FR) spectroscopy. The FR spectra obtained clearly demonstrate the effect of (a) the ball-milling, (b) the oxidative treatment and (c) the heat treatment on the sorption uptake processes involved in these treated samples.     

In vitro studies of carbon nanotubes biocompatibility

Cellular tests have been applied to study the biocompatibility of high purity multiwalled carbon nanotubes (MWNTs). The viability of fibroblasts, osteoblasts and osteocalcin concentrations in osteoblasts cultures in the presence of nanotubes has been examined, as well as the degree of cells stimulation, based on the amount of released collagen type I, IL-6 and oxygen free radicals. The high level of viability of the examined cells in contact with the nanotubes, the slight increase of collagen formation, the lack of pro-inflammatory IL-6 cytokine as well as the induction of free radicals, confirm a good biocompatibility of nanotubes, which is similar to that of polysulfone currently used in medicine. The collagen synthesis induced on nanotubes by both fibroblasts and osteoblasts may be significant for future medical applications of nanotubes, in particular as substrates for the regeneration of tissues.     

Effects of fullerenes and single-wall carbon nanotubes on murine and human macrophages

The discovery in 1985 of C-fullerenes, a novel carbon allotrope with a polygonal structure made up solely by 60 carbon atoms, and in 1991 of C-nanotubes, thin carbon filaments (1-3 μm in length and 0.001 μm in diameter) with extraordinary mechanical properties, opened a wide field of activity in carbon research. While toxicity and biocompatibility of C-fullerenes have been widely investigated, literature data concerning the biological properties and biotoxicity of C-nanotubes are poor and contradictory. Here we test the ability of highly purified C-Single-Walled-Nanotubes (SWNTs) and C-fullerenes to elicit an inflammatory response by murine and human macrophage cells in vitro. In order to determine the potential of these C-derivatives as biological inducers of inflammatory reactions we evaluate the ability of C-single-walled nanotubes and C-fullerenes to induce the release of NO by murine macrophages cells, to stimulate the phagocytic activity of human macrophage cells and to be cytotoxic against these cells. We show that SWNTs-C-nanotubes, when highly purified, as well as C-fullerenes, do not stimulate the release of NO by murine macrophage cells in culture, their uptake by human macrophage cells is very low, and they possess a very low toxicity against human macrophage cells.