Immobilization Of Multi-walled Carbon Nanotubes Research Articles

Synthesis of a Polymer Composite Based on a Modified Aminohumic Acid Tuned to a Sorbed Copper Ion

A composite based on amino-containing humic acid with the immobilization of multi-walled carbon nanotubes preliminarily tuned to a copper ion has been obtained. The synthesis of a composite pre-tuned for sorption by the local arrangement of macromolecular regions was obtained by introducing multi-walled carbon nanotubes and a molecular template into the composition of humic acid, followed by copolycondensation with acrylic acid amide and formaldehyde. The template was removed from the polymer network by acid hydrolysis. As a result of this tuning, the macromolecules of the composite "remember" conformations that are favorable for sorption, i.e., adsorption centers are formed in the polymer network of the composite, capable of repeated, highly specific interaction with the template and the highly selective extraction of target molecules from the solution. The reaction was controlled by the added amine and by the content of oxygen-containing groups. The structure and composition of the resulting composite were proven by physicochemical methods. A study of the sorption properties of the composite showed that after acid hydrolysis, the capacity increased sharply compared to a similar composite without tuning and a composite before hydrolysis. The resulting composite can be used as a selective sorbent in the process of wastewater treatment.

MWCNTs-Fe2O3nanoparticle nanohybrid-based highly sensitive electrochemicalsensor for the detection of kaempferol in broccoli samples

This work reports an electrochemical sensor with a modified glassy carbon electrode for the detection of kaempferol. The method was tailored by the immobilization of multiwalled carbon nanotubes (MWCNTs) assimilated with Fe$_{2}$O$_{3}$ nanoparticles (NPs) onto the electrode surface to detect kaempferol using differential pulse voltammetry. Thermogravimetric, transmission electron microscopic, cyclic, and differential voltammetric techniques were employed to characterize the developed electrochemical sensor. The kaempferol produces an anodic quasireversible peak at pH 6.6 in phosphate buffer with Fe$_{2}$O$_{3}$NPs/MWCNTs/GCE. The current of the anodic peak at 0.32 V increases linearly upon addition of kaempferol standard, resulting in Ip($\mu $A) = 1.577($\mu $M) $+$ 1.347 (R$^{2}$ = 0.9930). The limits of detection and limits of quantification were found to be 0.53 $\mu $M and 1.73 $\mu $M, respectively. Upon quantitative analysis of kaempferol in broccoli samples, it was found to be 3.78 $\mu $g g$^{-1}$ with an average percent recovery of 99.55%. The findings of this study identify the efficient catalytic property as a major contributor in the electron-transferring capacity from the electrode surface to the analyte, with promising possibilities of designing a highly sensitive electrochemical sensor for food industry applications.

A cobalt(II) phthalocyanine with indole substituents: formation, characterization and electrocatalytic studies

Herein, we report the formation of a new cobalt(II) phthalocyanine (CoPc) containing peripheral tetra-substituted indole (CoPc-ind, 2) moieties. The derivatized phthalonitrile, 4-(indole-4-oxy)phthalonitrile (1) as well its corresponding metal complex was characterized by NMR (for 1), IR– and UV–Vis spectroscopy as well as TOF mass spectrometry and elemental analysis (for 2). The electrochemical properties of the N4-macrocyclic metal complex were investigated using cyclic- and square-wave voltammetry as well as corroborated by UV–Vis spectroelectrochemistry. The CoPc was electrodeposited onto the surface of a Pt working electrode followed by the immobilization of multiwalled carbon nanotubes (MWCNTs) onto the modified working electrode surface. The electrocatalytic activity of the resultant modified electrode toward dopamine revealed a lower ΔE value of 80 mV versus Ag|AgCl for the modified (2-MWCNTs) Pt electrode compared to the bare Pt electrode (ΔE = 280 mV vs. Ag|AgCl). The diffusion- and convection-controlled electron-transfer kinetics of the chemically modified electrode were evaluated by chronoamperometry and rotating disk electrode techniques. Electrochemical impedance spectroscopic studies revealed that the 2-MWCNTs Pt electrode had a lower charge-transfer resistance and a higher apparent electron-transfer rate constant.

Correction: Preparation, characterization and analytical application of an electrochemical laccase biosensor towards low level determination of isoprenaline in human serum samples

A novel electrochemical biosensor has been developed based on the immobilization of multiwalled carbon nanotubes (MWCNT) on to a glassy carbon electrode (GCE) and subsequent casting of silica sol–gel (SiSG) entrapped laccase (Lac) enzyme on to the MWCNT/GCE. The catalytic activity of laccase biosensor was found to be good enough for sensitive determination of isoprenaline (ISP) with the aid of voltammetric techniques and we have also demonstrated the detailed electrochemical redox mechanism of ISP. From the effect of the pH, we have optimized the optimum pH as 6.5, and from effect of scan rate we have evaluated the kinetic parameters, heterogeneous rate constant, charge transfer coefficient and diffusion coefficient values. Furthermore the limit of detection (LOD) and limit of quantification (LOQ) values were found to be 1.8 × 10−7 M and 6.0 × 10−7 M, respectively. The simultaneous determination of ISP in the presence of uric acid (UA) and ascorbic acid (AA) was successfully carried out. The surface nature of the biosensor was characterized by using electrochemical impedance spectroscopy. Finally the validation of the proposed method was verified by the recovery of injection (ISP) in serum samples and their recoveries were found to be in a satisfactory range. The proposed method was found to have good repeatability, reproducibility and stability with low relative standard deviation (RSD) values.

Preparation, characterization and analytical application of an electrochemical laccase biosensor towards low level determination of isoprenaline in human serum samples

A novel electrochemical biosensor has been developed based on the immobilization of multiwalled carbon nanotubes (MWCNT) followed by sol–gel entrapment of laccase (Lac) enzyme on to the GCE.

Immobilized MWCNT support osteogenic cell culture

The broad use of versatile, strong, lightweight multi-walled carbon nanotubes (MWCNT) for use in biomaterial applications is tempered by ongoing debate about their safety. Recent reports suggest that factors such as their diameter and surface coating affect their function and cytotoxicity. The cell culture surfaces used in the current study were made of MWCNT immobilized in a high-density polyethylene substrate, differentiating it from most studies of MWCNT cytotoxicity. The purity, chemical functionalization, and immobilization of MWCNT were evaluated to elucidate their effect on MWCNT behavior relative to controls. While purity was found not to be significant in determining the behavior of cells on MWCNT relative to standard controls, the presence of carboxyl functional groups was generally associated with reduced cell metabolic activity, proliferation, and differentiation as measured using the MTS assay, nucleic acid incorporation, and alkaline phosphatase expression, respectively. This study demonstrates that the culture of osteogenic cells on surfaces made of nonfunctionalized and immobilized MWCNT is associated with a level of cell growth and differentiation comparable to those of standard tissue culture controls.

A disposable electrochemical immunosensor arrays using 4-channel screen-printed carbon electrode for simultaneous detection of Escherichia coli O157:H7 and Enterobacter sakazakii

An electrochemical immunosensor for Escherichia coli O157:H7 (E. coli O157:H7) and Enterobacter sakazakii (E. sakazakii) detection using carbon screen-printed low-density arrays is reported. The sensors were fabricated based on screen-printed carbon arrays containing four carbon working electrode, an integrated carbon counter electrodes and an integrated Ag/AgCl reference electrode. Multi-walled carbon nanotubes (MWCNTs)/sodium alginate (SA)/carboxymethyl chitosan (CMC) composite films were coated on all the working electrodes to enhance the sensitization of the electrode. Horseradish peroxidases (HRP) labeled antibodies of two bacteria were immobilize on different working electrode of the same screen-printed electrode respectively. The immobilization of MWCNTs, HRP labeled antibodies onto the screen-printed carbon electrodes was examined using atom force microscopy (AFM) and cyclic voltammetry (CV). The analytical performance of proposed immunosensor arrays toward E. sakazakii and E. coli O157:H7 was investigated by AFM and CV. Under optimal conditions, the linear range of E. sakazakii and E. coli O157:H7 were from 104 to 1010cfu/ml, with a detection limit of 4.57×103cfu/ml (S/N=3) and 3.27×103cfu/ml (S/N=3), respectively. The specificity, reproducibility, stability and accuracy of the proposed immunosensor arrays were also evaluated. Two antibodies modified work electrodes were tested and compared in terms of sensitivity and ability to recognize different pathogenic biological species.

Electrochemical sensor for bisphenol A determination based on MWCNT/melamine complex modified GCE

Abstract Based on the unique electronic properties and high adsorption capacity of carbon nanotubes as well as the electrostatic attraction between protonated melamine and negatively charged bisphenol A (BPA), a novel electrochemical sensor for the determination of BPA in water was fabricated by immobilization of multi-walled carbon nanotubes (MWCNTs)/melamine complex onto the surface of glassy carbon electrode. The cyclic voltammetry results showed that the sensor exhibited strong catalytic activity toward the oxidation of BPA with a well-defined cyclic voltammetric peak at 0.56 V. Moreover, the electrochemical sensor exhibited a wider linearity range from 10.0 nM to 40.8 μM BPA with a detection limit of 5.0 nM (S/N = 3). The enhanced performance of the sensor can be attributed to the combination of the excellent electrocatalytic property of MWCNTs and the electrostatic attraction of the protonated melamine to the negatively charged BPA. This novel sensor was successfully applied to determine BPA leached from real plastic samples with good recovery, ranging from 96% to 102%.

Chemical Immobilization of Multi-walled Carbon Nanotubes onto Glass Surface in Aqueous Media

Chemical Immobilization of Multi-walled Carbon Nanotubes onto Glass Surface in Aqueous Media

Amperometric Glucose Biosensor Electrode Modified with Carbon Nanotubes

The construction of biosensors based on nanostructures is an attractive challenge, mainly due to the properties of these materials. New strategies involved in the design of biosensors include nanoparticles, nanowires and carbon nanotubes; which is expected to impact on clinic diagnosis, environmental and food analysis. Within the enzyme biosensors, glucose biosensors are further development, mainly due to the impact of diabetes on society. In this paper, we propose a platform for the immobilization of multi-walled carbon nanotubes (CNT), using nafion and polyethylenimine as dispersants and glucose oxidase, allowing a significant improvement in the quantification of glucose.

Examination of incubation time of bare gold electrode inside cysteamine solution for immobilization of multi-walled carbon nanotubes on a gold electrode modified with cysteamine

A cysteamine (CysAm) nanostructure was generated to act as an intermediate layer between gold electrode and carbon nanotubes. A bare gold electrode was placed in a solution of CysAm to create a self-assembled monolayer on its surface. The modified electrode was then incubated with a solution of multi-walled carbon nanotubes. Cyclic voltammetry and atomic force microscopy were used to characterize the modified electrode. The results indicated that the number of functionalized MWCNTs on the surface of the electrodes increased by enhancing incubation time.

A novel hydrazine electrochemical sensor based on a carbon nanotube-wired ZnO nanoflower-modified electrode

ZnO nanoflowers were synthesized by a simple process (ammonia-evaporation-induced synthetic method) and were applied to the hydrazine electrochemical sensor. The prepared material was characterized by means of scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) and was then immobilized onto the surface of a glassy carbon electrode (GCE) via multi-walled carbon nanotubes (MWCNTs) to obtain ZnO/MWCNTs/GCE. The potential utility of the constructed electrodes was demonstrated by applying them to the analytical determination of hydrazine concentration. An optimized limit of detection of 0.18 μM was obtained at a signal-to-noise ratio of 3 and with a fast response time (within 3 s). Additionally, the ZnO/MWCNTs/GCE exhibited a wide linear range from 0.6 to 250 μM and higher sensitivity for hydrazine than did the ZnO modified electrode without immobilization of MWCNTs.

Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescence sensor based on carbon nanotube/organically modified silicate films

In this paper, a novel electrochemiluminescence (ECL) sensor was constructed to determine herring sperm (HS) double-stranded (ds) DNA. Tetramethoxysilane and dimethyldimethoxysilane were selected as co-precursors to form an organically modified silicate (ORMOSIL) film for the immobilization of multiwall carbon nanotubes (MWNTs) wrapped by poly( p-styrenesulfonate) (PSS), and then Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy) 3 2+) was successfully immobilized on a glassy carbon electrode via ion-association. PSS was employed to increase the conductivity of the ORMOSIL film and disperse the cut MWNTs, which were cut and shortened in a mixture of concentrated sulfuric and nitric acids, in the film. It was found that MWNTs could adsorb Ru(bpy) 3 2+ and acted as conducting pathways to connect Ru(bpy) 3 2+ sites to the electrode. MWNTs also played a key role as materials for the mechanical and thermal properties. The ECL performance of this modified electrode was evaluated in a flow injection analysis (FIA) system, and the detection limit ( S/ N = 3) for HS ds-DNA was 2.0 × 10 −7 g mL −1 with a linear range from 1.34 × 10 −6 to 6.67 × 10 −4 g mL −1 ( R 2 = 0.9876). In addition, the ECL sensor presented excellent characteristics in terms of stability, reproducibility and application life.

Catalytic oxidation of thiols at preheated glassy carbon electrode modified with abrasive immobilization of multiwall carbon nanotubes: applications to amperometric detection of thiocytosine, l-cysteine and glutathione

The performance of preheated glassy carbon electrode modified with carbon nanotubes is described. First glassy carbon electrode is heated for 5 min at 50 °C, then abrasive immobilization of multiwall carbon nanotubes on a preheated glassy carbon electrode was achieved by gentle rubbing of electrode surface on a filter paper supporting carbon nanotubes. Carbon nanotubes (CNTs)-modified glassy carbon electrodes exhibit strong and stable electrocatalytic response toward thiols oxidation in wide pH range. These properties permit an important decrease in over voltage for the oxidation of thiocytosine, glutathione and l-cysteine, as well as a dramatic increase in the peak currents in comparison with bare glassy carbon electrode. Furthermore, the thiols amperometric response of the coated electrodes is extremely stable, with more than 95% of the initial activity after 30 min stirring of 0.1 mM thiols. The electrocatalytic behavior is further exploited as a sensitive detection scheme for thiols detection by hydrodynamic amperometry. The substantial decrease in the overvoltage of the thiols oxidation associated with a stable amperometric response and antifouling properties of nanotubes films allow the development of highly sensitive thiols sensor without using any redox mediator. Such ability of carbon nanotubes to promote the thiols electron transfer reaction, short response time (5 s) and long-term stability, low detection limit, extended linear concentration range, high sensitivity suggest great promise for thiols amperometric sensors and detector for chromatographic analysis of thiol derivatives.

Abrasive immobilization of carbon nanotubes on a basal plane pyrolytic graphite electrode: application to the detection of epinephrine.

The performance of a basal plane pyrolytic graphite (bppg) electrode modified with carbon nanotubes is described. Abrasive immobilization of multiwall carbon nanotubes on a bppg electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes. The resulting electrode showed excellent mediation of epinephrine oxidation: a decrease in the overvoltage of the epinephrine electro-oxidation (200-500 mV) was observed as well as a dramatic increase in the peak current (4 times) compared to that seen at a bare bppg electrode. The oxidation peaks of epinephrine and ascorbic acid which overlap on bare bppg electrode were separated successfully (by ca. 220 mV) at the surface of the modified bppg electrode. The modified electrode showed good stability in comparison to most modified carbon nanotubes electrodes prepared by alternative methods.

In Vivo Monitoring of the Thiols in Rat Striatum by Liquid Chromatography with Amperometric Detection at a Functionalized Multi‐Wall Carbon Nanotubes Modified Electrode

AbstractA new chemically modified electrode (CME) was fabricated, which was based on the immobilization of multi‐wall carbon nanotubes fuctionalized with carboxylic group (MWNT‐COOH). The results indicated that the CME exhibited efficiently electrocatalytic oxidation for L‐cysteine and glutathione with relatively high sensitivity, stability and long‐life. Coupled with HPLC, the MWNT‐COOH CME was utilized for amperometric detection of the thiols. The peak currents of L‐cysteine and glutathione were linear to their concentrations ranging from 3.0×10−7 to 1.0×10−3 mol/L with the calculated detection limit (S/N=3) of 1.2×10−7, 2.2×10−7 mol/L, respectively. The method had been successfully applied to assess the contents of L‐cysteine and glutathione in rat striatal microdialysates.