Multilayer structured carbon nanotubes/poly-l-lysine/laccase composite cathode for glucose/O2 biofuel cell

Multilayer film of laccase, poly-l-lysine (PLL) and multi-walled carbon nanotubes (MWNTs) were prepared by a layer-by-layer self-assembly technique. The results of the UV–vis spectroscopy and scanning electron microscopy studies demonstrated a uniform growth of the multilayer. The catalytic behavior of the modified electrode was investigated. The (MWNTs/PLL/laccase)_n multilayer modified electrode catalyzed four-electron reduction of O₂ to water, without any mediator. The possible application of the laccase-catalyzed O₂ reduction at the (MWNTs/PLL/laccase)_n multilayer modified ITO electrode was illustrated by constructing a glucose/O₂ biofuel cell with the (MWNTs/thionine/AuNPs)₈ GDH film modified ITO electrode as a bioanode and the (MWNTs/PLL/laccase)₁₅ film modified ITO electrode as a biocathode. The open-circuit voltage reached to 700 mV, and the maximum power density achieved 329 μW cm⁻² at 470 mV of the cell voltage.     

Glucose biosensor based on new carbon nanotube-gold-titania nano-composites modified glassy carbon electrode

In this paper, a novel biosensor was prepared by immobilizing glucose oxidase （GOx） on carbon nanotube-gold-titania nanocomposites （CNT/Au/TiO2） modified glassy carbon electrode （GCE）. SEM was initially used to investigate the surface morphology of CNT/Au/TiO2 nanocomposites modified GCE, indicating the formation of the nano-porous structure which could readily facilitate the attachment of GOx on the electrode surface. Cyclic voltammogram （CV） and electrochemical impedance spectrum （EIS） were further utilized to explore relevant electrochemical activity on CNT]Au/TiO2 nanocomposites modified GCE. The observations demonstrated that the immobilized GOx could efficiently execute its bioelectrocatalytic activity for the oxidation of glucose. The biosensor exhibited a wider linearity range from 0.1 mmol L-1 to 8 mmol L^-1 glucose with a detection limit of 0.077 mmol L^- 1.     

Functional multiwalled carbon nanotube nanocomposite with iron picket-fence porphyrin and its electrocatalytic behavior

A kind of nanocomposite with good dispersion in water was prepared through noncovalent adsorption of iron picket-fence porphyrin (FeTMAPP), iron-5,10,15,20-tetrakis[αααα-2-trismethylammoniomethyl-phenyl]porphyrin, on multiwalled carbon nanotubes (MWNTs). UV–visible spectroscopic and electrochemical methods were used to characterize the nanocomposite. A gold nanoparticles/nanocomposite self-assembled monolayer was formed on gold electrode and showed highly synergetic behavior towards the electrocatalytic reduction of O₂ with a decrease of overpotential of 200 mV. FeTMAPP acted as the catalytic active center, and MWNTs increased the amount of FeTMAPP adsorbed and accelerated the electron transfer between FeTMAPP and electrode. The resulting biosensor exhibited good response to oxygen with a linear range from 0.52 to 180 μM and a detection limit of 0.38 μM, without the interference of ascorbic acid and uric acid, which showed an application potential of the proposed nanocomposite and monolayer in detection of dissolved oxygen and oxidase substrates.     

Electrochemical properties of niosomes modified Au electrode and DNA recognition

Non-ionic surfactant vesicles (NSVs), also referred to as niosomes, have been studied as an alternative to conventional liposomes. In this paper, electrochemical inspection of the interaction between Herring sperm DNA and niosomes has been investigated after a simple and novel method for the formation of niosomes on Au electrode. Each step of electrode modification has been confirmed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The assembly of octadecanethiol (ODT) layer on the electrode surface generates a packed film that introduces a barrier to the interfacial electron transfer (R_et), and the subsequent immobilization of niosomes onto the self-assembled monolayer (SAM) layer results in a further increase of R_et, due to the formed bilayer almost blocked the redox probe to the electrode surface. When Herring sperm DNA was added, the R_et value decreased, indicating that the barrier of the redox probe to the surface was disrupted. The addition of DNA caused the formation of some transmembrane channels for the redox probe across the niosomes. A good linear relationship between R_et value and DNA concentration was found over the 0–0.05 mg mL⁻¹ concentration range.     

A solid-state pH sensor based on WO3-modified vertically aligned multiwalled carbon nanotubes

In this communication, a novel solid-state pH sensor based on WO₃/MWNTs nanocomposite electrode will be reported. WO₃ nanoparticles were homogeneously coated on vertically aligned MWNTs by magnetron sputtering. Potentiometric pH response of the WO₃/MWNTs electrode in Britton–Robinson buffers revealed a linear working range from pH 2 to12 with a slope of about ?41 mV pH^?1 and a response time less than 90 s. The stability of the electrode remained over a month. Moreover, the WO₃/MWNTs electrode displayed excellent anti-interference property. Compared to conventional pH sensors, the pH sensor based on WO₃/MWNTs nanocomposite electrode also showed excellent reproducibility, high stability and superb selectivity.     

Rapid formation of well-ordered self-assembled monolayers of dodecanethiol on polycrystalline gold by microwave irradiation

This article reports a rapid method of preparing self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold by microwave irradiation (MWI, 650 W, duty cycle is 10%). The qualities of C₁₂SH-SAMs were characterized by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the C₁₂SH-SAMs formed by MWI in 120 s (C₁₂SH-SAMs_MWI,120 s) have low ionic permeability (the differential capacitance C_d values are independent of the scan rate and phase angle at 1 Hz Φ_1 Hz = 89 ± 0.9°), excellent electrochemical blocking ability towards the redox probe (the current i_MWI,120 s obtained from CV is lowest when compared to other SAMs and charge transfer resistance R_ct = (1.15 ± 0.19) × 10⁶ Ω cm²), and high surface coverage (99.996 ± 0.001%).     

Direct electron transfer of cytochrome c and its biosensor based on gold nanoparticles/room temperature ionic liquid/carbon nanotubes composite film

A robust and effective composite film based on gold nanoparticles (GNPs)/room temperature ionic liquid (RTIL)/multi-wall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode was prepared by a layer-by-layer self-assembly technique. Cytochrome c (Cyt c) was successfully immobilized on the RTIL-nanohybrid film modified GC electrode by electrostatic adsorption. Direct electrochemistry and electrocatalysis of Cyt c were investigated. The results suggested that Cyt c could be tightly adsorbed on the modified electrode. A pair of well-defined quasi-reversible redox peaks of Cyt c was obtained in 0.10 M, pH 7.0 phosphate buffer solution (PBS). RTIL-nanohybrid film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis currents increased linearly to the H₂O₂ concentration in a wide range of 5.0 × 10⁻⁵– 1.15 × 10⁻³ M. Based on the multilayer film, the third-generation biosensor could be constructed for the determination of H₂O₂.     

Cyclic voltammetric studies of carbohydrate–protein interactions on gold surface

A simple electrochemical method for the determination of association constants between carbohydrates and carbohydrate-binding proteins using cyclic voltammetry (CV) is described. The binding of concanavalin A (Con A) and cholera toxin (CT) to their specific α-mannose and β-galactose derivatives self-assembled on gold electrodes is electrochemically monitored with a redox probe of K₃Fe(CN)₆/K₄Fe(CN)₆. Upon binding of the proteins to the carbohydrate-modified electrodes, the redox current in CV decreases. The binding-induced change in electrochemical signal is thus used to construct Langmuir adsorption isotherm for the carbohydrate–protein interactions and to obtain the association constants. The association constants of carbohydrate–protein interactions determined by CV ((5.8 ± 1.2) × 10⁷ M^− 1 for mannose–Con A, (2.6 ± 0.5) × 10⁸ M^− 1 for galactose-CT) were in good agreement with those measured with electrochemical impedance spectroscopy and quartz crystal microbalance.     

Amperometric sensor for hydrogen peroxide based on direct electron transfer of spinach ferredoxin on Au electrode

A protein-based electrochemical sensor for hydrogen peroxide (H₂O₂) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe–2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)₆^3?/4? redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10 mM, pH 7.0 Tris–HCl buffer solution at ?170 and ?120 mV respectively. One electron reduction of the [2Fe-2S]²⁺ cluster occurs at one of the iron atoms to give the reduced [2Fe-2S]⁺. The formal reduction potential of Fdx ca. ?150 mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, k_s, for electron transfer between the Au electrode and Fdx was estimated to be 0.12 s^?1. From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H₂O₂. The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H₂O₂.The sensor calibration plot was linear with r² = 0.998 with sensitivity approximately 68.24 μAm M^?1 cm^?2. Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H₂O₂. Finally, the addition of H₂O₂ on MUA/Au electrode was observed which has no effect on amperometric current.     

Electrochemical synthesis of a ferrocenecarboxylic acid–C60 composite and its electrocatalysis to hydrogen peroxide

A new ferrocenecarboxylic acid–C₆₀ composite (Fc–C₆₀) has been synthesized by controlled potential electrolysis. A composite modified glassy carbon electrode has been prepared based on its good electrochemical activity. The modified electrode in 0.1 M NaClO₄ solution shows a reversible oxidation wave at E_1/2 = 0.32 V (vs. SCE) attributed to the oxidation of the ferrocene entity and a quasi-reversible reduction wave of C₆₀ entity at E_1/2 = ?0.54 V (vs. SCE). Electrocatalytic studies show that Fc–C₆₀ at the modified electrode can mediate the reduction of hydrogen peroxide (H₂O₂), and a broad linear range from 1.2 μM to 21.9 mM for H₂O₂ were obtained with a determination limit of 2.5 × 10^?7 M by amperometry.     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

A dysprosium nanowire modified carbon paste electrode for determination of levodopa using fast Fourier transformation square-wave voltammetry method

A new detection technique called the fast Fourier transform square-wave voltammetry (FFT-SWV) is based on the measurements of electrode admittance as a function of potential. The response of the detector (microelectrode) is fast, which makes the method suitable for most applications involving flowing electrolytes. The carbon paste electrode was modified by nanostructures to improve better sensitivity. The response is generated by a redox processes. The redox property of L-dopa was used for determination of it in human serum and urine samples. The support electrolyte that provided a more defined and intense peak current for L-dopa determination was at 0.05 mol l^?1 acetate buffer pH 7.0. Synthesized dysprosium nanowires make more effective surface like nanotubes [1], [2], [3], [4] so they are good candidates for using as a modifier for electrochemical reactions. The drug presented one irreversible oxidation peaks at 360 mV versus Ag/AgCl by modified nanowire carbon paste electrode which produced high current and reduced the oxidation potential about 80 mV.Furthermore, signal-to-noise ratio has significantly increased by application of discrete fast Fourier transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. To obtain the much sensitivity the effective parameters such as frequency, amplitude and pH was optimized. As a result, C_DL of 4.0 × 10^?9 M and an LOQ of 7.0 × 10^?9 M were found for determination for L-dopa. A good recovery was obtained for assay spiked urine samples and a good quantification of L-dopa was achieved in a commercial formulation.     

Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel sensor for the simultaneous determination of dopamine,ascorbic acid,and uric acid

A novel modified multiwall carbon nanotubes paste electrode with sodium dodecyl sulfate as a surfactant (SDS) has been fabricated through an electrochemical oxidation procedure and was used to electrochemically detect dopamine (DA), ascorbic acid (AA), uric acid (UA), and their mixture by cyclic voltammetry (CV) and differential voltammetry (DPV) methods. Several factors affecting the electrocatalytic activity of the hybrid material, such as the effect of pH, of the scan rate and of the concentration were studied. The bare carbon nanotubes paste electrode (BCNTPE) and SDS-modified carbon nanotubes paste electrode (SDSMCNTPE) were characterized using Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray spectroscopy (EDX). Using the CV procedure, a linear analytical curve was observed in the 1 × 10⁻⁶–2.8 × 10⁻⁵ M range with a detection limit at 3.3 × 10⁻⁷ M in pH 6.5, 0.2 M phosphate buffer solutions (PBS).     

An insight to the filtration mechanism of Pb(II) at the surface of a clay ceramic membrane through its preconcentration at the surface of a graphite/clay composite working electrode

The use of cyclic voltammetry (CV) and linear scan anodic stripping voltammetry (LSASV) to predict the selectivity of microfiltration ceramic membranes made from a lump of local clay towards Pb(II) ions filtration is described. The membranes were characterized by different techniques followed by CV analysis of the Fe(CN)₆^3-/Fe(CN)₆^4- redox couple and Pb(II) on bare graphite, raw clay, and clay-modified carbon paste electrode (clay-modified CPE). The effect of clay loading in the range of 1–10 % (w/w) on the electrodes is studied, where an enhanced peak current is observed for 5 % w/w clay. Moreover, a decrease in the peak current can be seen for bare graphite electrodes, suggesting that the clay mineral had played a substantial role in the sieving of heavy metal ions through the ceramic membrane. The electroactive surface area of 5% w/w raw clay towards Fe(II) ions was found to be in the order of 3.07 × 10^-2 cm² and higher than 5% w/w clay sintered to 1000 °C and bare graphite. CV analysis shows that both, 5 % w/w raw clay and 5 % w/w clay sintered to 1000 °C exhibited high peak currents towards Pb(II) ions. The mobility of the Pb(II) ions is found to increase when 5% w/w clay sintered to 1000 °C is utilized as membrane/electrode, leading to an increase in the amount of reduced Pb(II) ions on the surfaces of the clay membranes/electrodes. The study suggests successful filtration of Pb(II) ions through the proposed membrane/electrode and a much better accumulation than Fe(II) at the surface of the membrane/electrode before being subjected to filtration.     

A sensitivity-controlled hydrogen peroxide sensor based on self-assembled Prussian Blue modified electrode

In this communication, a hydrogen peroxide (H₂O₂) sensor based on self-assembled Prussian Blue (PB) modified electrode was reported. Thin film of PB was deposited on the electrode by self-assembly process including multiple sequential adsorption of ferric ions and hexacyanoferrate ions. The as-prepared PB modified electrode displayed sufficient stability for practical sensing application. At an applied potential of ?0.05 V vs. Ag/AgCl (sat. KCl), PB modified electrode with 30 layers exhibited a linear dependence on H₂O₂ concentration in the range of 1 × 10^?6–4 × 10^?4 M (r = 0.9998) with a sensitivity of 625 mA M^?1 cm^?2. It was found that the sensitivity of H₂O₂ sensors could be well controlled by adjusting the number of deposition cycles for PB preparation. This work demonstrates the feasibility of self-assembled PB modified electrode in sensing application, and provides an effective approach to control the sensitivity of PB-based amperometric biosensors.     

Fabrication of super-macroporous nanocomposites by deposition of carbon nanotubes onto polymer cryogels

Electrically conducting super-macroporous carbon nanotube/polymer cryogel nanocomposites were fabricated by a novel approach based on deposition of carbon nanotubes (CNTs) onto the inner surface of pre-formed cryogels assisted by cryogenic treatment. Stable aqueous dispersions of multi-walled and single-walled carbon nanotubes were firstly obtained by non-covalent modification of pristine nanotubes with either pyrene containing polydimethylacrylamide or poly(ethylene oxide)₂₆-b-poly(propylene oxide)₄₀-b-poly(ethylene oxide)₂₆ copolymers and, then, exploited for the preparation of nanocomposites. The mechanical and electrical properties of nanocomposite materials were measured and compared to similar materials prepared by established method. The novel approach provided super-macroporous nanocomposites with high electrical conductivity (>10^?2 S/m) at much lower nanotube content (0.12 wt.%).     

Electrochemical and thermodynamic properties of hexacyanoferrate(II)/(III) redox system on multi-walled carbon nanotubes

Novel films consist of multi-walled carbon nanotubes (MWCNT) were fabricated by means of catalytic chemical vapor deposition (CVD) technique with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene (FeCp₂) as catalyst. The electrochemical and thermodynamic behavior of the ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple on synthesized MWCNT-based films was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques at T = (278.15, 283.15, 293.15, and 303.15) K. The redox couple [Fe(CN)₆]^3−/4− behaves quasi-reversibly on fabricated MWCNT-based films and its reversibility is enhanced upon increasing temperature. Namely, the findings establish that with the rise in temperature the barrier for interfacial electron transfer decreases, leading, consequently, to an enhancement of the kinetics of the charge transfer process. According to thermodynamics the equilibrium of the redox process is shifted towards the formation of [Fe(CN)₆]³⁻ at elevated temperatures.     

Room-temperature ionic liquid as a new solvent to prepare high-quality dodecanethiol self-assembled monolayers on polycrystalline gold

This paper reports a new solvent, room-temperature ionic liquid (RTIL), for the preparation of dodecanethiol self-assembled monolayers (C₁₂SH-SAMs) on polycrystalline gold. The quality of C₁₂SH-SAMs was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From CV experiments, we find that the differential capacitance C_d values of the C₁₂SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) containing 10 μL neat C₁₂SH for 24 h (C₁₂SH-SAMs_{[BMIM]PF6,10 μL,24 h}) are independent of the scan rate, the effective thickness d_eff value and the average cant angle φ value of this monolayer are 18 ± 1 Å and 27 ± 4°, respectively. The difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.73 ± 0.18 μA cm⁻². EIS experiments show that the phase angle value at 1 Hz Φ_1 Hz, the charge transfer resistance R_ct value and surface coverage θ value of this C₁₂SH-SAM are 88.2 ± 0.7°, 3.44 ± 1.91 MΩ cm² and 99.998 ± 0.001%, respectively. These results indicate that high-quality C₁₂SH-SAMs can be formed in [BMIM]PF₆. In addition, the rate of formations of high-quality C₁₂SH-SAMs in RTIL can be substantially improved by ultrasound.     

Towards surface acid–base property of the carboxylic multi-walled carbon nanotubes by zero current potentiometry

The surface acid–base property of carboxylic multi-walled carbon nanotubes (MWNTs) is investigated by zero current potentiometry with a new electrochemical measurement system. The pH dependent interface potential variation at the interface of carboxylic MWNTs/solution is investigated by measuring zero current potential E_zcp. In the pH range of 1–11, the pH response of carboxylic MWNTs exhibits two linear relationships according to the following equations: E_zcp = 0.791–0.0535 pH (pH 1–5.1) and E_zcp = 0.643–0.0241 pH (pH 5.1–11), respectively. The intersection at pH 5.1 of two regions indicates the surface pK_a value of carboxylic group terminated MWNTs.     

Novel technique to form electrode–electrolyte nanointerface in all-solid-state rechargeable lithium batteries

The electrode–electrolyte nanocomposites, where the nano-sized NiS electrode with large capacity was embedded in the 80Li₂S · 20P₂S₅ electrolyte with high Li⁺ conductivity, were successfully prepared by the mechanochemical method. Contact area of solid–solid interface between the electrode and the electrolyte was remarkably increased in the nanocomposites. All-solid-state cell using the nanocomposites as a working electrode exhibited larger capacity and better cycling performance than the cell using the electrode obtained by conventional hand-mixing of powders. The mechanochemical technique sheds light on a new formation process of electrode–electrolyte interfaces endowing solid-state batteries with high power density and high energy density.