Mediated electrochemistry of dimethyl sulfoxide reductase promoted by carbon nanotubes

Mediated electrochemistry of dimethyl sulfoxide reductase from Rhodobacter capsulatus (DMSOR) which is immobilized on a bare glassy carbon (GC) electrode and a carbon nanotube (CNT)-modified GC electrode was studied using the Co complex (trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)cobalt(III) ([Co(trans-diammac)]³⁺) as a mediator. The cyclic voltammograms of different electrodes were carried out at different substrate (DMSO) concentrations. The results demonstrated that the catalytic current was increased by employing CNT as a promoter.     

Layer-by-layer electrostatic self-assembly of anionic and cationic carbon nanotubes

<正>The layer-by-layer(LBL) self assembly of anionic and cationic multi-walled carbon nanotubes(MWNTs) through electrostatic interaction has been carried out to fabricate all-MWNT multilayer films.The alternate uniform assembly of anionic and cationic MWNTs was investigated by UV-vis spectroscopy.Scanning electron microscopy(SEM) images displayed the growth of the MWNT films.     

Singling out the electrochemistry of individual single-walled carbon nanotubes in solution

Bandgap fluorescence spectroscopy of aqueous, micelle-like suspensions of SWNTs has given access to the electronic energies of individual semiconducting SWNTs, while substantially lower is the success achieved in the determination of the redox properties of SWNTs as individual entities. Here we report an extensive voltammetric and vis-NIR spectroelectrochemical investigation of true solutions of unfunctionalized SWNTs and determine the standard electrochemical potentials of reduction and oxidation as a function of the tube diameter of a large number of semiconducting SWNTs. We also establish the Fermi energy and the exciton binding energy for individual tubes in solution. The linear correlation found between the potentials and the optical transition energies is quantified in two simple equations that allow one to calculate the redox potentials of SWNTs that are insufficiently abundant or absent in the samples.     

Preparation and layer-by-layer self-assembly of positively charged multiwall carbon nanotubes

The report described a method of more stably dispersing oxidized carbon nanotubes (CNTs) by forming complex with polycation and the layer-by-layer self-assembly behavior of the complex with polyanion was studied. The properties of the self-assembled multilayer film containing carbon nanotubes were studied. Cyclic voltammetry, UV-vis-NIR spectroscopy, electrochemical impedance spectroscopy and scanning electron microscopy were used for characterization of film assembly. UV-vis-NIR spectroscopy and cyclic voltammetry study indicated the uniform growth of the film. Electrochemical impedance spectroscopy results showed that incorporating of carbon nanotubes in the polyelectrolyte multilayers decreased in the electron-transfer resistance R_ct, indicating more favorable electrochemical reaction interface. The electrocatalytic property of the multilayer modified electrode to NADH was investigated mainly with different numbers of the bilayers and the results showed that along with the increase of the assembled bilayers the overpotential of NADH oxidation decreased. The detection limit could reach 6 μM at a detection potential of 0.4 V.     

Magnetic carbon nanotubes: synthesis by electrostatic self-assembly approach and application in biomanipulations

Magnetic multiwalled carbon nanotubes (MWNTs) were facilely prepared by the electrostatic self-assembly approach. Poly(2-diethylaminoethyl methacrylate) (PDEAEMA) was covalently grafted onto the surfaces of MWNTs by MWNT-initiated in situ atom transfer radical polymerization (ATRP) of 2-diethylaminoethyl methacrylate (DEAEMA). The PDEAEMA-grafted MWNTs were quaternized with methyl iodide (CH(3)I), resulting in cationic polyelectrolyte-grafted MWNTs (MWNT-PAmI). Magnetic iron oxide (Fe(3)O(4)) nanoparticles were loaded onto the MWNT surfaces by electrostatic self-assembling between MWNT-PAmI and Fe(3)O(4), affording magnetic nanotubes. The assembled capability of the nanoparticles can be adjusted to some extent by changing the feed ratio of Fe(3)O(4) to MWNT-PAmI. The obtained magnetic nanotubes were characterized with TEM, EDS, STEM, and element mapping analyses. TEM and EDS measurements confirmed the nanostructures and the components of the resulting nanoobjects. The magnetic nanotubes were assembled onto sheep red blood cells in a phosphate buffer solution, forming magnetic cells. The blood cells attached with or without magnetic nanotubes can be selectively manipulated in a magnetic field. These results promise a general and efficient strategy to magnetic nanotubes and the fascinating potential of such magnetic nanoobjects in applications of bionanoscience and technology.     

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.     

Predominating stable adsorption and direct electrochemistry of glucose oxidase on carbon nanotubes by oxygen-containing groups

Stable adsorption and direct electrochemistry of glucose oxidase (GOx) occurred on nitric acid (HNO3)-treated multi-walled carbon nanotubes (MWNTs) instead of as-received MWNTs, demonstrating the critical roles of oxygen-containing groups in stableadsorption and direct electrochemistry of GOx on carbon nanotubes (CNTs).     

Layer-by-layer self-assembly of multiwalled carbon nanotube polyelectrolytes prepared by in situ radical polymerization

Anionic and cationic multiwalled carbon nanotube polyelectrolytes, prepared by covalent modification of multiwalled carbon nanotubes (MWCNTs) with poly(acrylic acid) and poly(acrylamide), were used for the layer-by-layer (LBL) self-assembly of MWCNTs on different substrates with polyelectrolytes, such as poly(diallyldimethylammonium chloride) and sodium poly(styrenesulfonate). Thermogravimetric analysis, Raman spectroscopy, and scanning electron microscopy (SEM) were used to demonstrate the modification of MWCNTs. Investigations using Fourier transform infrared spectroscopy, atomic force microscopy, SEM, and ultraviolet-visible spectroscopy proved this method to be practicable for preparing LBL films.     

Vertical self-assembly of modified multiwalled carbon nanotubes on gold surfaces induced by chitosan and Tween

Multiwalled carbon nanotubes modified with 2-aminoethanethiol (MWNT-AET) were vertically self-assembled on gold electrodes with the assistance of chitosan and Tween. According to AFM and cyclic voltammetric determinations the best results were achieved using chitosan.     

Myoglobin on multi-walled carbon nanotubes modified electrode: direct electrochemistry and electrocatalysis

Electrochemical behavior of myoglobin (Myb) incorporated on multi-walled carbon nanotubes (MWNTs) modified GC electrode is investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results indicate that Myb can be strongly adsorbed on the surface of the MWNT-modified electrode to form an approximate monolayer film. MWNTs can greatly promote the redox of horse heart Myb, on which a pair of well-defined and nearly reversible CV peaks for Myb Fe(III)/Fe(II) redox couple were obtained in pH 7.0 buffers. The formal potential of Myb on MWNT modified electrode shifts linearly with pH with a slope of −56.4 mV/pH, showing that the electron transfer is accompanied by single proton transportation. The high efficiency of the Myb/MWNT modified electrode towards the catalytic electro-reduction of nitric oxide has been observed. Potential application of Myb/MWNT modified electrode as biosensors to monitor NO is proposed.     

A study on the direct electrochemistry and electrocatalysis of microperoxidase-11 immobilized on a porous network-like gold film: Sensing of hydrogen peroxide

We have prepared porous and network-like nanofilms of gold by galvanic replacement of a layer of copper particles acting as a template. The films were first characterized by scanning electron microscopy and X-ray diffraction, and then modified with cysteamine so to enable the covalent immobilization of the enzyme microperoxidase-11. The immobilized enzyme undergoes direct electron transfer to the underlying electrodes, and the electrode displays high electrocatalytic activity towards the reduction of oxygen and hydrogen peroxide, respectively, owing to the largely enhanced electroactive surface of the porous gold film. The detection limit of H₂O₂ is 0.4 μM (3 S/N).

Amphiphilicity and self-assembly behaviors of polystyrene-grafted multi-walled carbon nanotubes in selective solvents

Multi-walled carbon nanotubes (MWCNTs) can self-assemble as cylindrical bundles in some solvents after polystyrene (PS) grafting. In these three-dimensional regular structures, the tubes are oriented and parallel arranged. Every self-assembly structure has an order head and a comparatively loose tail. In order to find out the role that solvent plays, MWCNTs were dispersed in several organic solvents before and after modification. Based on macroscopic stability of suspensions and microscopic state of nanotubes, compatibility between solvents and MWCNTs can be confirmed. According to compatibility difference between tubes and PS, five chosen solvents are divided into three groups: selective solvent, good solvent, and bad solvent. MWCNT-g-PS can self-assemble only in selective solvents. Tetrahydrofuran and benzene are well compatible with PS, but bad with MWCNTs. Driven by the solvent–philic/solvent–phobic interaction, MWCNT-g-PS self-organized regularly as bundles. Because each part of the MWCNT-g-PS is compatible well with 1,2-dichlorobenzene, gathering tendency of the modified tubes have been enervated by their good compatibility and weak amphiphilicity. Grafted or not, nanotubes reveal poor compatibility with methanol and ethanol. Strong incompatibility and limited amphiphilicity make MWCNT-g-PS agglomerate as quickly and irregularly as raw tubes. An adapted hydrophilic/lipophilic balance system is introduced to qualify compatibility and amphiphilicity of MWCNT-g-PS in each solvent. This novel model not only reveals the relationship between solvent and microscopic state of unmodified/modified tubes, but also signifies the decisive role of solvent in self-assembly behaviors of MWCNT-g-PS.     

Rebinding kinetics of dissociated amino acid ligand and carbon monoxide to ferrous microperoxidase-11 in aqueous solution

The rebinding kinetics of an amino acid ligand to ferrous microperoxidase-11 (MP11) after photolysis of aggregated ferrous MP11 was measured in aqueous solution with femtosecond transient visible absorption spectroscopy. The kinetics of CO rebinding to ferrous MP11 after photolysis of MP11CO was also measured in aqueous solution with femtosecond transient visible absorption spectroscopy. From these measurements, we found that either Val-11 or Lys-13 rebinds to ferrous MP11 exponentially with an 8 picosecond time constant in aggregated ferrous MP11 solution and that CO rebinds to ferrous MP11 nonexponentially with subnanosecond time scale in MP11CO solution. The kinetics of both the amino acid and CO rebinding to ferrous MP11 in MP11 system mimics that in carbon monoxide oxidation activator protein (CooA) or carboxymethyl cytochrome c (CmCytC) system. We also measured the kinetics of CO rebinding to ferrous MP11 in aqueous solution at different MP11CO concentrations and found that MP11CO concentration has an obvious effect on the kinetics of CO rebinding to ferrous MP11, where both the germinate yield and rate of CO rebinding to ferrous MP11 increase with the increase of MP11CO concentration. These findings suggested that the picosecond amino acid ligand rebinding process could disturb the proximal heme-ligand structure that possibly leads to the subnanosecond CO rebinding kinetics in MP11CO, CooACO and CmCytCCO systems.     

Aggregation and self-assembly of amphiphilic block copolymers in aqueous dispersions of carbon nanotubes

The self-assembly (SA) of amphiphilic block copolymers (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) was investigated in dispersions of single-walled and multiwalled carbon nanotubes (SWNT and MWNT, respectively) as a function of temperature. Differential scanning calorimetry (DSC) was used for characterization of the thermal behavior of the combined polymers-nanostructures system, and spin-probe electron paramagnetic resonance (EPR) was employed for probing the local dynamic and polarity of the polymer chains in the presence of nanostructures. It was found that SWNT and MWNT modify the temperature, enthalpy, and dynamic behavior of polymer SA. In particular, SWNT were found to increase the cooperativity of aggregating chains and dominate aggregate dynamics. MWNT reduced the cooperativity, while colloidal carbon black additives, studied for comparison, did not show similar effects. The experimental observations are consistent with the suggestion that dimensional matching between the characteristic radius of the solvated polymer chains and the dimensions of additives dominate polymer SA in the hybrid system.     

Bacteria capture, concentration and detection by alternating current dielectrophoresis and self-assembly of dispersed single-wall carbon nanotubes

The high polarizability and dielectrophoretic mobility of single-walled carbon nanotubes (SWNT) are utilized to capture and detect low numbers of bacteria and submicron particles in milliliter-sized samples. Concentrated SWNT solutions are mixed with the sample and a high-frequency (>100 kHz) alternating current (AC) field is applied by a microelectrode array to enhance bulk absorption of the particles (bacteria and nanoparticle substitutes) by the SWNTs via dipole-dipole interaction. The same AC field then drives the SWNT-bacteria aggregates to the microelectrode array by positive-AC dielectrophoresis (DEP), with enhanced and reversed bacteria DEP mobility due to the attached SWNTs. Since the field frequency exceeds the inverse RC time of the electrode double layer, the AC field penetrates deeply into the bulk and across the electrode gap. Consequently, the SWNTs and absorbed bacteria assemble rapidly (<5 min) into conducting linear aggregates between the electrodes. Measured AC impedance spectra by the same trapping electrodes and fields show a detection threshold of 10(4) bacteria/mL with this pathogen trapping and concentration technique.     

Direct electrochemistry and electrochemical catalysis of myoglobin-TiO2 coated multiwalled carbon nanotubes modified electrode

TiO(2) nanoparticles were homogeneously coated on multiwalled carbon nanotubes (MWCNTs) by hydrothermal deposition, and this nanocomposite might be a promising material for myoglobin (Mb) immobilization in view of its high biocompatibility and large surface. The glassy carbon (GC) electrode modified with Mb-TiO(2)/MWCNTs films exhibited a pair of well-defined, stable and nearly reversible cycle voltammetric peaks. The formal potential of Mb in TiO(2)/MWCNTs film was linearly varied in the range of pH 3-10 with a slope of 48.65 mV/pH, indicating that the electron transfer was accompanied by single proton transportation. The electron transfer between Mb and electrode surface, k(s) of 3.08 s(-1), was greatly facilitated in the TiO(2)/MWCNTs film. The electrocatalytic reductions of hydrogen peroxide were also studied, and the apparent Michaelis-Menten constant is calculated to be 83.10 microM, which shows a large catalytic activity of Mb in the TiO(2)/MWCNTs film to H(2)O(2). The modified GC electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant Mb-TiO(2)/MWCNTs modified glassy carbon electrode exhibited fast amperometric response to hydrogen peroxide reduction, long term life and excellent stability. Finally the activity of the sensor for nitric oxide reduction was also investigated.     

Covalent assembly of shortened multiwall carbon nanotubes on polyelectrolyte films and relevant electrochemistry study

A significant and versatile approach was developed for perpendicularly aligning multiwall carbon nanotubes on diverse substrates suitable for layer-by-layer self-assembly. The multiwall carbon nanotubes (s-MWNTs) used were shortened with oxidation under ultrasonic and functionalized with acyl chloride in thionyl chloride (SOCl2). The monolayer of s-MWNTs perpendicularly grafted to the substrate was obtained by dipping the polyelectrolyte modifying substrate into a tetrahydrofuran suspension of the functionalized s-MWNTs. The interaction proved to be stable and not liable to be affected by the ambience. Transmission electron microscopy and atomic force microscopy were used to examine the morphology of the MWNTs and s-MWNTs grafted on the substrates. Raman spectroscopy was applied to verify the existence of s-MWNTs for assembly, and Fourier transform infrared absorption spectra were used to investigate the interaction pattern between s-MWNTs and polyelectrolyte. The electrochemistry properties of the monolayer of s-MWNTs when the substrate was indium-tin oxide were studied.     

Isosteric heat of argon adsorbed on single-walled carbon nanotubes prepared by laser ablation

We have measured 21 adsorption isotherms for argon on single-walled carbon nanotubes produced by laser ablation. We explored temperatures between 40 and 153 K to obtain the coverage dependence of the isosteric heat of adsorption for films in the first and second layers. Our data are compared to results obtained in computer simulation studies and to data obtained in previous experimental investigations of this system.     

The effects of the lengths and orientations of single-walled carbon nanotubes on the electrochemistry of nanotube-modified electrodes

The influence of both nanotube orientation and length on the electrochemical properties of electrodes modified with single-walled carbon nanotubes was investigated. Gold electrodes were modified with either randomly dispersed or vertically aligned nanotubes to which ferrocenemethylamine was attached. Electron transfer kinetics were found to depend strongly on the orientation of the nanotube, with electron transfer between the gold electrode and the ferrocene moiety being 40 times slower through randomly dispersed nanotubes than through vertically aligned nanotubes. The difference is hypothesized to be due to electron transfer being more direct through a single tube than that with electrodes modified with randomly dispersed nanotubes. With the vertically aligned nanotubes the rate constant for electron transfer varied inversely with the mean length of the nanotubes. The results indicate there is an advantage in using aligned carbon nanotube arrays over randomly dispersed nanotubes for achieving efficient electron transfer to bound redox active species such as in the case of bioelectronic or photovoltaic devices.