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Abstract: We have developed a polyaniline/carboxy-functionalized multiwalled carbon nanotube (PAn/MWCNTCOOH) nanocomposite by blending the emeraldine base form of polyaniline (PAn) and carboxy-functionalized multiwalled carbon nanotubes (MWCNT) in dried dimethyl sulfoxide (DMSO) at room temperature. The conductivity of the resulting PAn/MWCNTCOOH was 3.6×10−3 Scm−1, mainly as a result of the protonation of the PAn with the carboxyl group and the radical cations of the MWCNT fragments. Horseradish peroxidase (HRP) was immobilized within the PAn/MWCNTCOOH nanocomposite modified Au (PAn/MWCNTCOOH/Au) electrode to form HRP/PAn/MWCNTCOOH/Au for use as a hydrogen peroxide (H2O2) sensor. The adsorption between the negatively charged PAn/MWCNTCOOH nanocomposite and the positively charged HRP resulted in a very good sensitivity to H2O2 and an increased electrochemically catalytical current during cyclic voltammetry. The HRP/PAn/MWCNTCOOH/Au electrode exhibited a broad linear response range for H2O2 concentrations (86μM–10mM). This sensor exhibited good sensitivity (194.9μAmM−1 cm−2), a fast response time (2.9s), and good reproducibility and stability at an applied potential of −0.35V. The construction of the enzymatic sensor demonstrated the potential application of PAn/MWCNTCOOH nanocomposites for the detection of H2O2 with high performance and excellent stability. [Copyright &y& Elsevier]

Abstract: Multi-walled carbon nanotubes (MWCNT)/polyelectrolyte (PE) hybrid thin films were fabricated by alternatively depositing negatively charged MWCNT and positively charged (diallyldimethylammonium chloride) (PDDA) via layer-by-layer (LbL) assembly technique. The stepwise growth of the multilayer films of MWCNT and PDDA was characterized by UV–vis spectroscopy. Scanning electron microscopy (SEM) images indicated that the MWCNT were uniformly embedded in the film to form a network and the coverage density of MWCNT increased with layer number. Au nanoparticles (NPs) could be further adsorbed onto the film to form PE/MWCNT/Au NPs composite films. The electron transfer behaviour of multilayer films with different compositions were studied by cyclic voltammetry using [Fe(CN)6]3−/4− as an electrochemical probe. The results indicated that the incorporation of MWCNT and Au NPs not only greatly improved the electronic conductivity of pure polyelectrolyte films, but also provided excellent electrocatalytic activity towards the oxidation of nitric oxide (NO). [Copyright &y& Elsevier]

Abstract: In this paper, the gold nanorods (GNRs)/multiwalled carbon nanotubes (CNT) composite film-modified glassy carbon (GC) electrode was fabricated simply by the electrostatic interaction between the positively charged GNRs and the negatively charged CNT. And the GNRs/CNT/GC electrode was used for the selective and sensitive determination of dopamine (DA) in the presence of ascorbic acid (AA). It was found that the GNRs/CNT/GC electrode had higher catalytic activity towards the oxidation of DA and ascorbic acid (AA) comparing with the bare GC and CNT/GC electrodes. It may be due to the synergic effect of GNRs and CNT, because the surface area of the GNRs/CNT/GC electrode increased, the edge plan sites presented on the CNT surface can improve the electron transfer between the modified electrode and DA, and the rod-shaped gold may be served as the mediator for the oxidation of dopamine and provided the electrocatalytic ability. Moreover, the voltammetric peaks of AA and DA were separated enough at the GNRs/CNT/GC electrode, which was sufficiently enough for the selective determination of DA. Thus, the selective determination of DA was carried out with low detection limit (0.8nM, S/N=3). Also it was obtained that the proposed method was feasible to detect the concentration of DA in human blood serum. Therefore, it can be concluded that the GNRs/CNT modified electrode may be advantageous for the DA determination. [Copyright &y& Elsevier]

Abstract: Au/MWCNTs catalysts were synthesised by chemical reduction and tested as anode electrodes in a glucose microfluidic fuel cell as a function of time at different temperatures. Physicochemical characterisation of Au/MWCNTs showed an average particle size of approximately 4nm with high dispersion among the MWCNTs support. The use of MWNTCs as support provides chemical stability and good performance for microfluidic fuel cells. The maximum power density reached with Au/MWCNTs was 0.28mWcm−2. Chronoamperometric testing (4h) at three operating temperatures (15, 25 and 35°C) demonstrated that the use of Au/MWCNTs as anode electrodes showed better stability compared with that of Au/C. [Copyright &y& Elsevier]

Abstract: Three-way data obtained from different pulse heights of differential pulse voltammetry (DPV) was analyzed using multivariate curve resolution by alternating least squares (MCR-ALS) algorithm. Differential pulse voltammograms of tryptophan were recorded at a gold nanoparticles decorated multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNTs-nanoAu). The determination of tryptophan was performed even in the presence of unexpected electroactive interference(s). Both the simulated and experimental data were non-bilinear. Therefore a potential shift algorithm was used to correct the observed shift in the data. After correction, the data was augmented and MCR-ALS was applied to the augmented data. A relative error of prediction of less than 8% for the determination of the simulated analyte of interest and tryptophan in synthetic samples indicated that the methodology employing voltammetry and second-order calibration could be applied to complex analytical systems. [Copyright &y& Elsevier]

Abstract: A novel electrochemical sensing interface, electrodeposition of gold–platinum alloy nanoparticles (Au–PtNPs) on carbon nanotubes, was proposed and used to fabricate a label-free amperometric immunosensor. On the one hand, the multiwalled carbon nanotubes (MWCNTs) could increase active area of the electrode and enhance the electron transfer ability between the electrode and redox probe; on the other hand, the Au–PtNPs not only could be used to assemble biomolecules with bioactivity kept well, but also could further facilitate the shuttle of electrons. In the meanwhile, horseradish peroxidase (HRP) instead of bovine serum albumin (BSA) was employed to block the possible remaining active sites and avoid the nonspecific adsorption. With the synergetic catalysis effect of Au–PtNPs and HRP towards the reduction of hydrogen peroxide (H2O2), the signal could be amplified and the sensitivity could be enhanced. Using alpha-fetoprotein (AFP) as model analyte, the fabricated immunosensor exhibited two wide linear ranges in the concentration ranges of 0.5–20ngmL−1 and 20–200ngmL−1 with a detection limit of 0.17ngmL−1 at a signal-to-noise of 3. Moreover, the immunosensor exhibited good selectivity, stability and reproducibility. The developed protocol could be easily extended to other protein detection and provided a promising potential in clinical diagnosis application. [Copyright &y& Elsevier]

Abstract: An electrochemical sensor based on gold nanoparticles (GNPs)/multiwalled carbon nanotubes (MWCNTs)/poly (1,5-naphthalenediamine) films modified glassy carbon electrode (GCE) was fabricated. The effectiveness of the sensor was confirmed by sensitive detection of cellobiose dehydrogenase (CDH) gene which was extracted from Phanerochaete chrysosporium using polymerase chain reaction (PCR). The monomer of 1,5-naphthalenediamine was electropolymerized on the GCE surface with abundant free amino groups which enhanced the stability of MWCNTs modified electrode. Congo red (CR)-functionalized MWCNTs possess excellent conductivity as well as high solubility in water which enabled to form the uniform and stable network nanostructures easily and created a large number of binding sites for electrodeposition of GNPs. The continuous GNPs together with MWCNTs greatly increased the surface area, conductivity and electrocatalytic activity. This electrode structure significantly improved the sensitivity of sensor and enhanced the DNA immobilization and hybridization. The thiol modified capture probes were immobilized onto the composite films-modified GCE by a direct formation of thiol–Au bond and horseradish peroxidase–streptavidin (HRP–SA) conjugates were labeled to the biotinylated detection probes through biotin–streptavidin bond. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the film assembly and DNA hybridization processes. The amperometric current response to HRP-catalyzed reaction was linearly related to the common logarithm of the target nucleic acid concentration in the range of 1.0×10−15–1.0×10−10 M, with the detection limit of 1.2×10−16 M. In addition, the electrochemical biosensor exhibited high sensitivity, selectivity, stability and reproducibility. [Copyright &y& Elsevier]

Abstract: Two layers of cationic iron(III) meso-tetrakis (N-methylpyridinum-4-yl)porphyrin (FeTMPyP) and anionic gold nanoparticles (GNPs) were alternately assembled on a poly(diallyldimethylammonium chloride)-wrapped carbon nanotube (PDDA-CNT)-modified electrode via electrostatic interactions. The porphyrin-functionalized gold nanoparticles were characterized by scanning electron microscopy and UV–vis absorption spectrometry. The (FeTMPyP–GNP)2/PDDA-CNT modified electrode showed two stable and well-defined peaks at −0.112V and −0.154V, which were attributed to the GNP-accelerated redox process of Fe(III)TMPyP/Fe(II)TMPyP. The modified electrode possessed excellent electrocatalytic behavior for the reduction of peroxyacetic acid (PAA). The resulting biosensor exhibited a fast amperometric response to PAA (∼3s), with a wide linear range from 2.5×10−6 M to 1.05×10−3 M and a detection limit of 0.5μM at a signal-to-noise ratio of 3. More importantly, H2O2 did not interfere with the detection. Thus, this biosensor enabled highly sensitive detection of PAA without removing H2O2 and showed a promising potential in practical applications. [Copyright &y& Elsevier]

Abstract: A new strategy for the sensitive detection of biomarker using Prussian blue–carbon nanotubes/gold nanocomposites (GNPs–PB–CNTs) as labels and horseradish peroxidase (HRP) as an enhancer is presented herein. Chitosan hydrogel and TiO2 nanocomposites were first coated onto a glassy carbon electrode (GCE) surface, which provided a biocompatible interface with abundant –NH2 groups for the immobilization of primary antibodies (Ab1). The detectable signal was recorded and amplified based on a sandwich-type immunoassay by the employment of HRP-labeled secondary antibodies (HRP-Ab2) and GNPs–PB–CNTs bioconjugates according to the electrocatalytic reduction of H2O2 by bound HRP in the presence of PB. Using human chorionic gonadotropin (HCG) as a model analyte, experimental results showed that the prepared HRP-Ab2–GNPs–PB–CNTs bioconjugates exhibited satisfactory redox activity and high efficiency of enzyme catalysis. Under optimized conditions, the immunosensor showed a low detection limit of 0.023mIU/mL HCG, with a linear range from 0.05 to 150mIU/mL. The proposed method exhibited high sensitivity, acceptable stability and reproducibility, and could be extended to detect other protein targets. [Copyright &y& Elsevier]

Abstract: A novel composite electrode of Au/ZnO/MWCNTs/GC has been constructed for the electrochemical detection of nitrite, where ZnO thin film and Au nanoparticles are electrodeposited through layer-by-layer onto MWCNTs/GC substrate. The resulting electrode is characterized by scanning electron microscopy and energy-dispersed X-ray spectroscopy. Its electrocatalytic activity toward the electro-oxidation of nitrite has been examined and compared to various modified electrodes, including MWCNTs/GC, Au/ZnO/GC, Au/MWCNTs/GC, and ZnO/MWCNTs/GC via cyclic voltammetry. The electrodeposition time for ZnO and the Au loading amount together with the solution pH are investigated to achieve optimal conditions for the electrode fabrication and nitrite detection. Linear relationship between current response and nitrite concentration is observed in the range from 7.8×10−7 to 4.0×10−4 M and the limit of the detection is 4.0×10−7 M (S/N=3). The influence of various anions and cations on the nitrite detection has been studied. The proposed method is also employed for the determination of nitrite in real samples. [Copyright &y& Elsevier]

Abstract: Gold nanoparticle-functionalized carbon nanotubes (AuNP-CNT) have been prepared by a novel self-assembly method. The new material has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) and utilized for constructing AuNP-CNT-modified pyrolytic graphite electrode (AuNP-CNT/PGE) to investigate the electrochemical behavior of L-dopa in neutral phosphate buffer solution. Compared to bare PG electrode, AuNP-CNT/PGE shows novel properties towards the electrochemical redox of L-dopa in phosphate buffer solution at pH 7.0. The oxidation potential of L-dopa shows a significant decrease at the AuNP-CNT/PGE. The oxidation current of L-dopa is about 5-fold higher than that of the unmodified PGE. Using differential pulse voltammetry (DPV) method, the oxidation current is well linear with L-dopa concentration in the range of 0.1–150μM, with a detection limit of about 50nM (S/N=3). The proposed electrode can also effectively avoid the interference of ascorbic acid and uric acid, making the proposed sensor suitable for the accurate determination of L-dopa in both pharmaceutical preparations and human body fluids. [Copyright &y& Elsevier]

Abstract: We outline here the fabrication of a sensitive electrochemical DNA biosensor for the detection of sequence-specific target DNA. Zinc oxide nanowires (ZnONWs) were first immobilized on the surface of a glassy carbon electrode. Multi-walled carbon nanotubes (MWCNTs) with carboxyl groups were then dropped onto the surface of the ZnONWs. Gold nanoparticles (AuNPs) were subsequently introduced to the surface of the MWNTs/ZnONWs by electrochemical deposition. A single-stranded DNA probe with a thiol group at the end (HS–ssDNA) was covalently immobilized on the surface of the AuNPs by forming an Au–S bond. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to investigate the film assembly process. Differential pulse voltammetry (DPV) was used to monitor DNA hybridization by measuring the electrochemical signals of [Ru(NH3)6]3+ bounding to double-stranded DNA (dsDNA). The incorporation of ZnONWs and MWCNTs in this sensor design significantly enhances the sensitivity and the selectivity. This DNA biosensor can detect the target DNA quantitatively in the range of 1.0×10−13 to 1.0×10−7 M, with a detection limit of 3.5×10−14 M (S/N=3). In addition, the DNA biosensor exhibits excellent selectivity, even for single-mismatched DNA detection. [Copyright &y& Elsevier]

Abstract: In this work, a highly sensitive electrochemical sensor for the determination of tryptophan (Trp) was fabricate by electrodeposition of gold nanoparticles (AuNPs) onto carbon nanotube (CNT) films pre-cast on a glassy carbon electrode (GCE), forming an AuNP–CNT composite-modified GCE (AuNP–CNT/GCE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for the surface analysis of the electrode. The results indicate that the hybrid nanomaterials induced a substantial decrease in the overpotential of the Trp oxidation reaction and exhibited a remarkable synergistic effect on the electrocatalytic activity toward the oxidation of Trp. In phosphate buffer solution (pH 7.4), the modified electrode showed excellent analytical performance for the amperometric determination of Trp. The peak currents possess a linear relationship with the concentration of Trp in the range of 30nM to 2.5μM, and the detection limit is 10nM (S/N=3). In addition, the modified electrode was used to determine Trp concentration in pharmaceutical samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: In this paper, a novel reagentless amprometric immunosensor was built on the conductive multilayer, comprised of Nafion-coated multi-wall carbon nanotubes (MWCNT), thionine (Thi) and gold nanoparticles (nano-Au). First, Nafion-MWCNT homogeneous composite was dropped on the surface of the glass carbon electrode (GCE). Then Thi was chemisorbed by both carboxylic MWCNT and cation exchanger Nafion. Furthermore, the negative-charged nano-Au, which was used to immobilize biomolecules, was chemisorbed onto Thi film through the electrostatic force with the amino groups of Thi. The stepwise self-assembly process of the immunosensor was characterized by means of cyclic voltammetry (CV), and the microstructure of modified film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using α-1-fetoprotein (AFP) as a model, this novel immunosensor presented amplified sensitivity, good stability, and a broader linear response in two ranges from 0.5–20ng/mL and 20–200ng/mL with a detection limit of 0.26ng/mL, as well as good selectivity and storage stability. [Copyright &y& Elsevier]

Abstract: A monolayer of –NH2 terminated 3-aminopropyltriethoxysilane (APS) was self-assembled onto a p-type silicon (100) substrate. This amine terminated silane monolayer provided an electrostatic point of attachment for citrate stabilised gold colloid nanoparticles, which act as ‘seed’ particles for the electroless deposition of gold, creating an electrolessly deposited gold layer on silicon. A –NH2 terminated cysteamine monolayer was then deposited onto the gold layer and carbon nanotubes, with high carboxylic acid functionality, were immobilised via a condensation reaction. A redox active molecule ferrocenemethanol was then chemically attached to the immobilised carbon nanotubes. These nanostructures were used as working electrodes in cyclic voltammetry to observe the oxidation and reduction of ferrocene. Important electrochemical parameters such as electrode kinetics, electron transfer rate and surface concentration of the redox active molecules were obtained, providing information on the ability of electroless plated gold surfaces to act as supports for carbon nanotube-based electrodes. This information has also provided insights into the behaviour of vertically aligned carbon nanotubes immobilised on nanoscale gold wires, which have been previously fabricated using atomic force microscopy. [Copyright &y& Elsevier]