A sensitive electrochemical sensor for nitrobenzene (NB) detection has been developed based on macro-/meso-porous carbon materials (MMPCMs). MMPCMs were prepared by pyrolysis of the ionic-liquid ([AEIm]BF4) polymer (PIL) pre-wrapped onto SiO2 microspheres and then removal of the silica core. The morphology and structure of MMPCMs were characterized by scanning electron microscopy (SEM) and nitrogen adsorption/desorption measurements. Owing to the macro-/meso-porous structure, large specific surface area and accumulation effect of MMPCMs, the MMPCMs modified glassy carbon (MMPCMs/GC) electrode has high catalytic activity towards the reduction of NB. At the optimal pH value and accumulation time, the resulted electrochemical sensor shows satisfactory analytical performance for NB detection. The linear response range is from 0.2 μM to 40 μM and the detection limit is 8 nM based on the signal-to-noise ratio of 3. Moreover, the MMPCMs/GC electrode exhibits good stability and reproducibility, and acceptable selectivity.

We report a facile method for the synthesis of hollow platinum nanospheres/carbon nanotubes nanohybrids (CNTs-G-PtHNs). Silver nanoparticles were used as sacrificial templates and uniformly deposited on the functionalized carbon nanotubes (CNTs). By galvanic replacement reaction between CNTs-supported silver and PtCl62−, well-dispersed hollow platinum nanospheres (PtHNs) were “grown” on CNTs. The morphology and electrochemical properties of the CNTs-G-PtHNs nanohybrids have been investigated by transmission electron microscopy and cyclic voltammetry, respectively. PtHNs in the CNTs-G-PtHNs nanohybrids have an average diameter of about 8 nm and the CNTs-G-PtHNs nanohybrids have higher electrochemical surface area and better electrocatalytic performance towards methanol oxidation than CNTs-A-PtHNs nanohybrids which were obtained by adsorbing the pre-synthesized PtHNs onto CNTs. Most importantly, the long-term stability of CNTs-G-PtHNs nanohybrids for methanol electro-oxidation has obviously improved compared with that of the CNTs-A-PtHNs nanohybrids.Graphical abstractHighlights► Synthesis of hollow platinum nanospheres/carbon nanotubes nanohybrids. ► Hollow platinum nanospheres with high dispersion “grown” on CNTs. ► The obtained nanohybrids show excellent stability for methanol oxidation.

Graphite oxide (GO) was used to accelerate the graphitization of furan resin carbon. The effects of the GO content and the heat-treatment temperature (HTT) on the graphitization of furan resin carbon were investigated. The X-ray diffraction results indicate that the graphitization extent of furan resin carbon increases with the increase of the GO content and the HTT.

DNA methylation catalyzed by methyltransferase (MTase) is a significant epigenetic process for modulating gene expression. Traditional methods to study MTase activity require a laborious and costly DNA labeling process. In this article, we report a simple, colorimetric, and label-free methylation-responsive DNAzyme (MR-DNAzyme) strategy for MTase activity analysis. This new strategy relies on horseradish peroxidase (HRP) mimicking DNAzyme and the methylation-responsive sequence (MRS) of DNA which can be methylated and cleaved by the MTase/endonuclease coupling reaction. Methylation-induced scission of MRS would activate the DNAzyme that can catalyze the generation of a color signal for the amplified detection of methylation events. Taking Dam MTase and DpnI endonuclease as examples, we have developed two colorimetric methods based on the MR-DNAzyme strategy. The first method is to utilize an engineered hairpin-DNAzyme hybrid probe for facile turn-on detection of Dam MTase activity, with a wide linear range (6−100 U/mL) and a low detection limit (6 U/mL). Furthermore, this method could be easily expanded to profile the activity and inhibition of restriction endonuclease. The second method involves a methylation-triggered DNAzyme-based DNA machine, which achieves the ultrahigh sensitive detection of Dam MTase activity (detection limit = 0.25 U/mL) by a two-step signal amplification cascade.

A new amperometric glucose biosensor has been developed based on platinum (Pt) nanoparticles/polymerized ionic liquid-carbon nanotubes (CNTs) nanocomposites (PtNPs/PIL-CNTs). The CNTs was functionalized with polymerized ionic liquid (PIL) through directly polymerization of the ionic liquid, 1-vinyl-3-ethylimidazolium tetrafluoroborate ([VEIM]BF4), on carbon nanotubes and then used as the support for the highly dispersed Pt nanoparticles. The electrochemical performance of the PtNPs/PIL-CNTs modified glassy carbon (PtNPs/PIL-CNTs/GC) electrode has been investigated by typical electrochemical methods. The PtNPs/PIL-CNTs/GC electrode shows high electrocatalytic activity towards the oxidation of hydrogen peroxide. Taking glucose oxidase (GOD) as the model, the resulting amperometric glucose biosensor shows good analytical characteristics, such as a high sensitivity (28.28 μA mM−1 cm−2), wide linear range (up to 12 mM) and low detection limit (10 μM).

A novel strategy for fabricating the sensitive and stable biosensor was present by layer-by-layer (LBL) self-assembling glucose oxidase (GOD) on multiwall carbon nanotube (CNT)-modified glassy carbon (GC) electrode. GOD was immobilized on the negatively charged CNT surface by alternatively assembling a cationic poly(ethylenimine) (PEI) layer and a GOD layer. And the direct electrochemistry of GOD in the self-assembled {GOD/PEI}n film was investigated. CNT as an excellent nanomaterial greatly improved the direct electron transfer between GOD in {GOD/PEI}n film and the electrode. And the ultrathin {GOD/PEI}n film on the CNT surface provided a favorable microenvironment to keep the bioactivity of GOD. Moreover, PEI used as an out-layer was adsorbed on the top of the {GOD/PEI}n film to form the sandwich-like structure (PEI/{GOD/PEI}n), improving the stability of the enzyme electrode. On basis of these, the developed PEI/{GOD/PEI}n/CNT/GC biosensor has a high sensitivity of 106.57 μA mM−1 cm−2, and can measure as low as 0.05 mM glucose. In addition, the biosensor has excellent operational stability with no decrease in the activity of enzyme over a 1-week period. Therefore, the developed strategy making use of the advantages of CNT and LBL assembly is ideal for the direct electrochemistry of the redox enzymes and the construction of the sensitive and stable enzyme biosensor.

Graphene nanosheets, synthesized by a modified Hummers method, have been functionalized by PMo12, and used as the supports of the PtRu nanoparticles. The electrocatalytic properties of the resultant nanocatalysts (PtRu/PMo12-Graphene) for methanol electro-oxidation have been evaluated by cyclic voltammetry and chronoamperometry. The micrograph and the elemental composition have also been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopy. The results suggest that the addition of PMo12 benefits the high dispersion of graphene nanosheets in the water and the uniform dispersion of the PtRu nanoparticles on the graphene nanosheets, and the PtRu/PMo12-Graphene catalysts have higher electrocatalytic activity and better electrochemical stability for methanol oxidation compared to the PtRu/Graphene catalysts.

Polymerized ionic liquid-wrapped carbon nanotubes (PIL-CNTs) were firstly designed for direct electrochemistry and biosensing of redox proteins. The CNTs were coated successfully with polymerized ionic liquid (PIL) layer, as verified by transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The PIL-CNTs were dispersed better in water and showed superior electrocatalysis toward O2 and H2O2 comparing to pristine CNTs and the mixture of IL monomer and CNTs. With glucose oxidase (GOD) as a protein model, the direct electrochemistry of the redox protein was investigated on the PIL-CNTs modified glassy carbon (GC) electrode and excellent direct electrochemical performance of GOD molecules was observed. The proposed biosensor (GOD/PIL-CNTs/GC electrode) displayed good analytical performance for glucose with linear response up to 6 mM, response sensitivity of 0.853 μA mM−1, good stability and selectivity.

A novel label-free electrochemical strategy for monitoring the activity and inhibition of protein kinase is developed, based on the linkage between the phosphorylated peptide and DNA functionalized Au nanoparticles (DNA–AuNPs) by Zr4+ and the chronocoulometric response of [Ru(NH3)6]3+ absorbed on the DNA–AuNPs.

A simple and ultrasensitive label-free electrochemical impedimetric aptasensor for thrombin based on the cascaded signal amplification was reported. The sandwich system of aptamer/thrombin/aptamer-functionalized Au nanoparticles (Apt-AuNPs) was fabricated as the sensing platform. The change of the interfacial feature of the electrode was characterized by electrochemical impedance analysis with the redox probe [Fe(CN)6]3−/4−. For improving detection sensitivity, the three-level cascaded impedimetric signal amplification was developed: (1) Apt-AuNPs as the first-level signal enhancer; (2) the steric-hindrance between the enlarged Apt-AuNPs as the second-level signal amplification; (3) the electrostatic-repulsion between sodium dodecylsulfate (SDS) stabilized Apt-AuNPs and the redox probe [Fe(CN)6]3−/4− as the third-level signal amplification. Enlargement of Apt-AuNPs integrated with negatively charged surfactant (SDS) capping could not only improve the detection sensitivity of the impedimetric aptasensor for thrombin but also present a simple and general signal-amplification model for impedimetric sensor. The aptasensor based on the enlargement of negatively charged Apt-AuNPs showed an increased response of the electron-transfer resistance to the increase of thrombin concentration through a wide detection range from 100 fM to 100 nM. The linear detection range was 0.05−35 nM, and thrombin was easily detectable to a concentration of 100 fM. The aptasensor also has good selectivity and reproducibility.

In this paper, a bifunctional electrochemical biosensor for highly sensitive detection of small molecule (adenosine) or protein (lysozyme) was developed. Two aptamer units for adenosine and lysozyme were immobilized on the gold electrode by the formation of DNA/DNA duplex. The detection of adenosine or lysozyme could be carried out by virtue of switching structures of aptamers from DNA/DNA duplex to DNA/target complex. The change of the interfacial feature of the electrode was characterized by cyclic voltammertic (CV) response of surface-bound [Ru(NH3)6]3+. On the other hand, DNA functionalized Au nanoparticles (DNA-AuNPs) were used to enhance the sensitivity of the aptasensor because DNA-AuNPs modified interface could load more [Ru(NH3)6]3+ cations. Thus, the assembly of two aptamer-contained DNA strands integrated with the DNA−AuNPs amplification not only improves the sensitivity of the electrochemical aptasensor but also presents a simple and general model for bifunctional aptasensor. The proposed aptasensor has low detection limit (0.02 nM for adenosine and 0.01 μg mL−1 for lysozyme) and exhibits several advantages such as high sensitivity and bifunctional recognition.

A boron-doped carbon nanotube (BCNT)-modified glassy carbon (GC) electrode was constructed for the detection of l-cysteine (L-CySH). The electrochemical behavior of BCNTs in response to l-cysteine oxidation was investigated. The response current of L-CySH oxidation at the BCNT/GC electrode was obviously higher than that at the bare GC electrode or the CNT/GC electrode. This finding may be ascribed to the excellent electrochemical properties of the BCNT/GC electrode. Moreover, on the basis of this finding, a determination of L-CySH at the BCNT/GC electrode was carried out. The effects of pH, scan rate and interferents on the response of L-CySH oxidation were investigated. Under the optimum experimental conditions, the detection response for L-CySH on the BCNT/GC electrode was fast (within 7 s). It was found to be linear from 7.8 × 10−7 to 2 × 10−4 M (r = 0.998), with a high sensitivity of 25.3 ± 1.2 nA mM−1 and a low detection limit of 0.26 ± 0.01 μM. The BCNT/GC electrode exhibited high stability and good resistance against interference by other oxidizable amino acids (tryptophan and tyrosine).

SnO2-carbon nanotubes (CNTs) composites were prepared by sol–gel method, and characterized by scanning electron microscopy and X-ray diffraction. Due to high stability in diluted acidic solution, SnO2-CNTs composites were selected as the catalyst support and second catalyst for ethanol electrooxidation. The electrocatalytic properties of the SnO2-CNTs supported platinum (Pt) catalyst (Pt/SnO2-CNTs) for ethanol oxidation have been investigated by typical electrochemical methods. Under the same mass loading of Pt, the Pt/SnO2-CNTs catalyst shows higher electrocatalytic activity and better long-term cycle stability than Pt/SnO2 catalyst. Additionally, the effect of the mass ratio of CNTs to SnO2 on the electrocatalytic activity of the electrode for ethanol oxidation was investigated, and the optimum mass ratio of CNTs to SnO2 in the Pt/SnO2-CNTs catalyst is 1/6.3.

A simple method for the spontaneous deposition of manganese oxides on the surface of polyacrylonitrile (PAN)-based carbon fibers by a direct redox reaction between carbon fibers and permanganate ions is described. Catalytic graphitization of the PAN-based carbon fibers coated with manganese oxides was investigated by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results indicate that the graphitization of the PAN-based carbon fibers was accelerated in the presence of the manganese oxides even at the relatively low temperature of 1,600 °C.

The Boron-doped carbon nanotubes (BCNTs) modified glassy carbon (GC) electrode was obtained simply and used for highly selective and sensitive determination of dopamine (DA). Comparing with the bare GC and CNTs/GC electrodes, the BCNTs have higher catalytic activity toward the oxidation of DA and ascorbic acid (AA). Moreover, the voltammetric peaks of AA and DA were separated enough (ca. 238 mV) at the BCNTs/GC electrode, which is superior to that at the CNTs/GC electrode (ca. 122 mV). Thus, the selective determination of DA was carried out successfully in the presence of AA. A wide concentration range (2.0 × 10−8–7.5 × 10−5 M) and low detection limit (1.4 nM, S/N = 3) for the DA detection were obtained. The possibility of the BCNTs/GC electrode for the determination of DA in human blood serum has also been evaluated. The advantageous properties of this electrode for the DA determination lie in its excellent catalytic activity, selectivity and simplicity. The more edge plane sites presented on the BCNTs surface were partially responsible for its good analytical behavior.

A sensitive, label free electrochemical aptasensor for small molecular detection has been developed in this work based on gold nanoparticles (AuNPs) amplification. This aptasensor was fabricated as a tertiary hybrid DNA–AuNPs system, which involved the anchored DNA (ADNA) immobilized on gold electrode, reporter DNA (RDNA) tethered with AuNPs and target-responsive DNA (TRDNA) linking ADNA and RDNA. Electrochemical signal is derived from chronocoulometric interrogation of [Ru(NH3)6]3+ (RuHex) that quantitatively binds to surface-confined DNA via electrostatic interaction. Using adenosine triphosphate (ATP) as a model analyte and ATP-binding aptamer as a model molecular reorganization element, the introduction of ATP triggers the structure switching of the TRDNA to form aptamer–ATP complex, which results in the dissociation of the RDNA capped AuNPs (RDNA–AuNPs) and release of abundant RuHex molecules trapped by RDNA–AuNPs. The incorporation of AuNPs in this strategy significantly enhances the sensitivity because of the amplification of electrochemical signal by the RDNA–AuNPs/RuHex system. Under optimized conditions, a wide linear dynamic range of 4 orders of magnitude (1 nM–10 μM) was reached with the minimum detectable concentration at sub-nanomolar level (0.2 nM). Those results demonstrate that our nanoparticles-based amplification strategy is feasible for ATP assay and presents a potential universal method for other small molecular aptasensors.

Ru-doped SnO2 nanoparticles were prepared by chemical precipitation and calcinations at 823 K. Due to high stability in diluted acidic solution, Ru-doped SnO2 nanoparticles were selected as the catalyst support and second catalyst for methanol electrooxidation. The micrograph, elemental composition, and structure of the Ru-doped SnO2 nanoparticles were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. The electrocatalytic properties of the Ru-doped SnO2-supported Pt catalyst (Pt/Ru-doped SnO2) for methanol oxidation have been investigated by cyclic voltammetry. Under the same loading mass of Pt, the Pt/Ru-doped SnO2 catalyst shows better electrocatalytic performance than the Pt/SnO2 catalyst and the best atomic ratio of Ru to Sn in Ru-doped SnO2 is 1/75. Additionally, the Pt/Ru-doped SnO2 catalyst possesses good long-term cycle stability.The Pt/Ru-doped SnO2 catalyst shows better electrocatalytic performance for methanol electrooxidation than the Pt/SnO2 catalyst and the best atomic ratio of Ru to Sn in Ru-doped SnO2 is 1/75.

The well-aligned carbon nanotube arrays (ACNTs) were used as supporting material and the γ-MnO2/ACNT electrode with high dispersion of γ-MnO2 has been prepared by electrochemically induced deposition method. The crystal structure and morphology of the γ-MnO2/ACNT electrode were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The capacitive properties of γ-MnO2/ACNT electrode were characterized by cyclic voltammetry and galvanostatic charge–discharge method. The specific capacitance of the γ-MnO2/ACNT electrode is as high as 784 F g− 1 based on γ-MnO2 and 234 F g− 1 based on γ-MnO2/ACNT composites in 0.1 M Na2SO4 aqueous solution from 0 to 1 V when the charge–discharge current density is 1 mA cm− 2. Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge–discharge cycle stability.

The conductive polymer poly(neutral red) polymerized on a graphite electrode (PNR/graphite) as a support material was used for catalytic oxidation of ethanol in acidic solution and investigated by electrochemical methods. Pt particles loaded on the surface of PNR/graphite electrode exhibited higher electrocatalytic activity for ethanol oxidation in comparison with Pt particles supported directly on graphite. With the equivalent loading mass of Pt catalyst, the special activity (SA) at peak a of the Pt/PNR/graphite electrode polymerized for 10 cycles in 5 × 10−4 M NR + 0.5 M H2SO4 solution is 3,478 A C−1 and about 2.20 times higher than that of the Pt/graphite electrode (1,582 A C−1). The results show that the electrochemical performance of Pt catalyst for ethanol oxidation is improved by the addition of PNR

Doped carbon nanotubes are now extremely attractive and important nanomaterials in bioanalytical applications due to their unique physicochemical properties. In this paper, the boron-doped carbon nanotubes (BCNTs) were used in amperometric biosensors. It has been found that the electrocatalytic activity of the BCNTs modified glassy carbon (GC) electrode toward the oxidation of hydrogen peroxide is much higher than that of the un-doped CNTs modified electrode due to the large amount of edge sites and oxygen-rich groups located at the defective sites induced by boron doping. Glucose oxidase (GOD) was selected as the model enzyme and immobilized on the BCNTs modified glassy carbon electrode by entrapping GOD into poly(o-aminophenol) film. The performance of the sensor was investigated by electrochemical methods. At an optimum potential of +0.60 V and pH 7.0, the biosensor exhibits good characteristics, such as high sensitivity (171.2 nA mM−1), low detection limit (3.6 μM), short response time (within 6 s), satisfactory anti-interference ability and good stability. The apparent Michaelis–Menten constant (Kmapp) is 15.19 mM. The applicability to the whole blood analysis of the enzyme electrode was also evaluated.

The electrooxidation of ethanol on Pt/ZSM-5 zeolite-C catalyst was investigated in sulfuric acid aqueous solution. Because of high stability in general acidic solution, ZSM-5 zeolite particles were selected as the support and the second catalyst. The micrograph and elemental composition of Pt/ZSM-5 zeolite particles were characterized by scanning electron microscopy and energy disperse X-ray spectroscopy. The electrocatalytic properties of Pt/ZSM-5 zeolite-C catalyst for ethanol oxidation have been investigated by cyclic voltammetry. Under the same Pt-loading mass and experimental conditions for ethanol oxidation, Pt/ZSM-5 zeolite-C catalyst shows higher activity than Pt/C catalyst. Additionally, Pt/ZSM-5 zeolite-C catalyst possesses good long-term cycle stability. The results indicate that Pt/ZSM-5 zeolite-C catalyst may have good potential application in direct ethanol fuel cell.

Due to their high stability in general acidic solutions, SiO2 nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt–SiO2 nanocatalysts were prepared in this paper. The micrography and elemental composition of Pt–SiO2 nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The electrocatalytic properties of Pt–SiO2 nanocatalysts for ethanol oxidation were investigated by cyclic voltammetry. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt–SiO2 nanocatalysts show higher activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts. Additionally, Pt–SiO2 nanocatalysts possess good anti-poisoning ability. The results indicate that Pt–SiO2 nanocatalysts may have good potential applications in direct ethanol fuel cells.Due to good stability in general acidic solution, SiO2 nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt–SiO2 nanocatalysts with 1–2 nm show higher electrocatalytic activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts.

This paper reports on the greatly improved electrochemical properties of prussian blue (PB) by multi-walled carbon nanotubes (MWNTs). PB was efficiently deposited on the MWNTs modified pyrolytic graphite (PG) electrode. The microstructure and electrochemical behavior of the PG/MWNTs/PB electrodes were investigated by scanning electron microscopy and cyclic voltammetry, respectively. Compared with the PG/PB electrode, the PG/MWNTs/PB electrode shows much better electrochemical stability, much wider pH adaptive range and larger response current to the reduction of hydrogen peroxide (H2O2). Amperometric response of the PG/MWNTs/PB electrode to H2O2 at neutral solution pH was also investigated.

Organic molecule neutral red (NR), as electron transfer mediator, was introduced in the anodic electrocatalyst system for methanol oxidation and the resulting electrode was investigated by cyclic voltammetry, polarization method, and electrochemical impedance spectroscopy. For the same loading mass of platinum catalyst, 1.25 times larger exchange current density, 1.83 times higher specific activity, and better long-term cycle stability can be obtained at Pt/NR/graphite electrode, as compared to the electrode without NR. These results indicate that neutral red plays an important role on the enhanced electrocatalytic activity of platinum catalyst for methanol oxidation.

A simple and sensitive label-free electrochemical immunoassay electrode for detection of carcinoembryonic antigen (CEA) has been developed. CEA antibody (CEAAb) was covalently attached on glutathione (GSH) monolayer-modified gold nanoparticle (AuNP) and the resulting CEAAb–AuNP bioconjugates were immobilized on Au electrode by electro-copolymerization with o-aminophenol (OAP). Electrochemical impedance spectroscopy and cyclic voltammetry studies demonstrate that the formation of CEA antibody–antigen complexes increases the electron transfer resistance of [Fe(CN)6]3−/4− redox pair at the poly-OAP/CEAAb–AuNP/Au electrode. The use of CEA antibody–AuNP bioconjugates and poly-OAP film could enhance the sensitivity and anti-nonspecific binding of the resulting immunoassay electrode. The preliminary application of poly-OAP/CEAAb–AuNP/Au electrode for detection of CEA was also evaluated.

Electrochemical oxidation and determination of glutathione (GSH) were investigated with well-aligned carbon nanotube (CNT) arrays. Square wave voltammetric and amperometric results suggest that aligned-CNT electrode exhibits excellent electrochemical activity and good anti-fouling property for direct electrochemical oxidation of glutathione. Also, the preliminary application of the aligned-CNT electrode for amperometric determination of glutathione was evaluated.

Immobilization and electro-oxidation of calf thymus double-stranded deoxyribonucleic acid (dsDNA) were investigated at carbon nanotube (CNT) electrode modified with ethylene diamine. Well-defined oxidation peak and large peak current of dsDNA oxidation have been observed even at very low dsDNA concentration (40 ng mL−1). Interaction between promethazine hydrochloride and immobilized dsDNA was also investigated. The intercalative binding of promethazine hydrochloride with dsDNA results in an increase of electrochemical impedance and a decrease of dsDNA oxidation peak current. The possibility using functional CNT electrode immobilized dsDNA to sense promethazine hydrochloride was also explored.

A polyaniline (PANI)/carbon nanotubes (CNTs) composite modified electrode was fabricated by galvanostatic electropolymerization of aniline on multi-walled carbon nanotubes (MWNTs)-modified gold electrode. The electrode thus prepared exhibits enhanced electrocatalytic behavior to the reduction of nitrite and facilitates the detection of nitrite at an applied potential of 0.0 V. Although the amperometric responses toward nitrite at MWNTs/gold and PANI/gold electrodes have also been observed in the experiments, these responses are far less than that obtained at PANI/MWNTs/gold electrode. The effects of electropolymerization time, MWNTs concentration and pH value of the detection solution on the current response of the composite modified electrode toward sodium nitrite, were investigated and discussed. A linear range from 5.0 × 10−6 to 1.5 × 10−2 M for the detection of sodium nitrite has been observed at the PANI/MWNTs modified electrode with a sensitivity of 719.2 mA M−1 cm−2 and a detection limit of 1.0 μM based on a signal-to-noise ratio of 3.

Amperometric glucose biosensor is developed, based on immobilization of glucose oxidase (GOD), in an electrochemically polymerized non-conducting poly(o-aminophenol) (POAP) film at copper (Cu)-modified gold (Au) electrode. The rough surface and the ability to electrochemically oxidize glucose of Cu nanoparticles result in the improvement of the detection limit and the increase of the maximum response current and sensitivity. The biosensor based on Au/Cu/POAP/GOD electrode has two times lower detection limit, three times larger maximum current and 2.5 times higher sensitivity than those of the biosensor based on Au/POAP/GOD electrode. Additionally, the fast response time, large response current and good selectivity for ascorbic acid, uric acid and acetaminophen can also be obtained. On the other hand, effects of electrochemical deposition time of Cu, applied potential used in the determination and electroactive compounds on the amperometric response of the enzymatic sensor were investigated and discussed. Excellent reproducibility and stability of biosensor are also observed.

Platinum (Pt) electrocatalyst was electrochemically dispersed on well-aligned carbon nanotube (CNT) arrays by a potential-step method. The structure and elemental composition of the resulting Pt/CNT electrode were characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic properties of the Pt/CNT electrode for oxygen reduction reaction have been investigated by linear sweep voltammetry. Compared with a Pt/graphite electrode, higher electrocatalytic activity of the Pt/CNT electrode can be observed. This may be attributed to the high dispersion of platinum catalysts and the particular properties of CNT supports. The results imply that the Pt/CNT has good potential applications in proton exchange membrane fuel cells.

A new amperometric biosensor, based on adsorption of glucose oxidase (GOD) at the platinum nanoparticle-modified carbon nanotube (CNT) electrode, is presented in this article. CNTs were grown directly on the graphite substrate. The resulting GOD/Pt/CNT electrode was covered by a thin layer of Nafion to avoid the loss of GOD in determination and to improve the anti-interferent ability. The morphologies and electrochemical performance of the CNT, Pt/CNT, and Nafion/GOD/Pt/CNT electrodes have been investigated by scanning electron microscopy, cyclic voltammetry, and amperometric methods. The excellent electrocatalytic activity and special three-dimensional structure of the enzyme electrode result in good characteristics such as a large determination range (0.1–13.5 mM), a short response time (within 5 s), a large current density (1.176 mA cm−2), and high sensitivity (91 mA M−1 cm−2) and stability (73.5% remains after 22 days). In addition, effects of pH value, applied potential, electrode construction, and electroactive interferents on the amperometric response of the sensor were investigated and discussed. The reproducibility and applicability to whole blood analysis of the enzyme electrode were also evaluated.

The electrochemical deposition and the electrocatalytic properties of platinum (Pt) nanoparticles on carbon nanotube electrode have been investigated in this paper. Carbon nanotubes (CNTs) used in this paper are grown directly on graphite disk by chemical vapor deposition (CVD). The Pt nanoparticles are synthesized by potentiostatic method from 1.3 mM chloroplatinic acid + 0.5 M sulfuric acid aqueous solution at −0.25 V. The micrographs of Pt/CNTs/graphite electrode are characterized by scanning electron microscopy (SEM). The electrocatalytic properties of Pt/CNTs/graphite electrodes for methanol oxidation have been investigated by cyclic voltammetry (CV) in 1.0 M CH3OH+0.5 M H2SO4 aqueous solutions and the excellent electrocatalytic activity (AQ, defined by peak current density per unit of Pt deposition charge) can be observed even at low platinum deposition charge (Q=1.24×10−4 C cm−2). At Q=3.72×10−3 C cm−2, the highest electrocatalytical activity of Pt/CNTs/graphite electrode reaches 4.62 A C−1 and is about 2.3 times as high as that of Pt/graphite electrode. This may be attributed to the unique structure and high surface area of carbon nanotubes and also suggests that CNTs have good potential applications as catalyst supports in direct methanol fuel cell (DMFC). On the other hand, the long-term stability of Pt/CNTs/graphite electrode has also been investigated.

Carbon nanotubes are grown directly on the graphite substrate using a simple catalyst prepared by electrochemical deposition in this paper. Compared with the current preparation methods of catalysts, electrochemical deposition is an effective, cheap and simple technique. By adjusting the electrodeposition parameters (current density and deposition time), the effects of the morphology and the particle size of iron (Fe) catalyst on the synthesis of carbon nanotubes have also been investigated. Furthermore, carbon nanotube Y junctions can be observed in this work.

A novel label-free electrochemical strategy for monitoring the activity and inhibition of protein kinase is developed, based on the linkage between the phosphorylated peptide and DNA functionalized Au nanoparticles (DNA–AuNPs) by Zr4+ and the chronocoulometric response of [Ru(NH3)6]3+ absorbed on the DNA–AuNPs.