Noncovalently functionalized water-soluble multiwall-nanotubes through azocarmine B and their application in nitric oxide sensor

A new noncovalent approach for the dissolution of MWNTs in water by azocarmine B (ACB) is reported. Through a simple electro-polymerization procedure, a novel electrochemical NO sensor based on water-soluble MWNTs and polyazocarmine B (PACB) nanofilm electrode was prepared, which showed excellent electrocatalytic activity towards the oxidation of nitric oxide (NO). The oxidation current linearly increased with the nitric oxide concentration in the range of 2.2 × 10⁻⁷–1.2 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.8 × 10⁻⁸ mol L⁻¹. The sensor has the merit of good stability, reproducibility, high sensitivity and selectivity, and it can be used to monitor NO released from rat liver cells effectively.     

Microstructure control of WO3 film by adding nano-particles of SnO2 for NO2 detection in ppb level

To fabricate more excellent NO₂ sensor with high sensor response and good linearity between the sensor response and NO₂ concentration, the microstructure of WO₃ lamellae was controlled by adding nano-particles of SnO₂. It was found that the sintering of WO₃ lamellae was inhibited by adding nano-particles of SnO₂. The device using WO₃ lamellae added a small amount of SnO₂ nano-particles had the highest sensor response, exhibiting a high sensor response (S = 60-540) even to dilute NO₂ (100–1000 ppb) in air at 200°C.     

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.     

Self-assembly of bilayer lipid membrane at multiwalled carbon nanotubes towards the development of photo-switched functional device

Bilayer lipid membrane (BLM) was self-assembled on a uniquely fabricated hydrophilic surface, containing N atoms from the carbon source of ethylene amine, of the multi-walled carbon nanotubes (MWNTs) to form the BLM/MWNTs nanocomposites. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and photoelectric experiments were taken to study the properties of the BLM/MWNTs nanocomposites. The thickness of the BLM, which was calculated from the CV data obtained at BLM/MWNTs electrode, turned out to be 4.38 nm, suggesting that the lipid self-assembled at the nanotubes surface was consistent with a bilayer structure. C₆₀-incorporated BLM could also be self-assembled at the nanotubes surface (C₆₀-BLM/MWNTs). The formation of BLM on the MWNTs surface blocked the diffusion of [Fe(CN)₆]^3/4− redox ions across BLM to the MWNTs electrode as no redox current was observed by CV measurement, whereas the incorporation of the electron mediator, C_60, resumed a pair of redox peaks at C₆₀-BLMs/MWNTs electrode. Moreover, the incorporation of C₆₀ led to a four order of magnitude reduction of the resistance of C₆₀-BLM/MWNTs (369.3 Ω) than that of BLM/MWNTs (3.238 × 10⁶ Ω). MWNTs electrode exhibited an intrinsic cathodic photocurrent (166 μA cm⁻²) while BLM/MWNTs electrode blocked photocurrent response of the MWNTs. Interestingly, C₆₀-BLM/MWNTs electrode resumed partial photoelectric properties (photo current: 65 μA cm⁻²) due to the electron mediation effect of C₆₀ incorporated into the lipid membrane. As a result, the novel self-assembled BLM/MWNTs nanocomposites provided a simple yet useful model to study the C₆₀-mediated photoelectric properties of the BLM/MWNTs which may be applicable to develop new biosensors and molecular devices.     

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.     

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.     

Non-enzymatic detection of hydrogen peroxide using a functionalized three-dimensional graphene electrode

A novel three-dimensional (3D) electrochemical sensor was developed for highly sensitive detection of hydrogen peroxide (H₂O₂). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the electrode scaffold. Using in-situ polymerized polydopamine as the linker, the 3D electrode was functionalized with thionine molecules which can efficiently mediate the reduction of H₂O₂ at close proximity to the electrode surface. Such stable non-enzymatic sensor is able to detect H₂O₂ with a wide linear range (0.4 to 660 μM), high sensitivity (169.7 μA mM^− 1), low detection limit (80 nM), and fast response (reaching 95% of the steady current within 3 s). Furthermore, this sensor was used for real-time detection of dynamic release of H₂O₂ from live cancer cells in response to a pro-inflammatory stimulant.     

Novel core–shell SDC/amorphous Na2CO3 nanocomposite electrolyte for low-temperature SOFCs

Novel core–shell SDC (Ce_0.8Sm_0.2O_1.9)/amorphous Na₂CO₃ nanocomposite was prepared for the first time. The core–shell nanocomposite particles are smaller than 100 nm with amorphous Na₂CO₃ shell of 4–6 nm in thickness. The nanocomposite electrolyte shows superionic conductivity above 300 °C, where the conductivity reaches over 0.1 S cm⁻¹. Such high conductive nanocomposite has been applied in low-temperature solid oxide fuel cells (LTSOFCs) with an excellent performance of 0.8 W cm⁻² at 550 °C. A new potential approach of designing and developing superionic conductors for LTSOFCs was presented to develop interface as ‘superionic highway’ in two-phase materials based on coated SDC.     

A novel non-enzymatic electrochemical glucose sensor modified with FeOOH nanowire

The recent development in the nanotechnology has paved the way for large number of new materials and devices of desirable properties which have useful functions for electrochemical sensor and biosensor applications. In this paper, a novel enzymeless glucose sensor is developed on the discovery that the FeOOH nanowire in fact possesses an intrinsic enzyme mimetic electrocatalytic activity similar to that found in natural peroxidases. The electrode modified with FeOOH nanowires showed a wide linear range (15 μM–3 mM) and high sensitivity (12.13 μA mM^? 1) for glucose sensing. Other excellent performances such as highly reproducible response, long-term stability, sound mechanical and chemical stability are also observed, and the interferences of ascorbic acid and dopamine can almost be completely avoided. The good analytical performance, low cost and straightforward preparation method made this novel electrode material promising for the development of effective glucose sensors.     

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.     

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.     

Needle-like IrO/Ag combined pH microelectrode

In this study, a combined pH microelectrode has been developed consisting of an indicator electrode made of IrO₂ prepared using the polymeric precursor method and deposited in a platinum microwire. This electrode was mounted inside a stainless steel needle, the external surface of which was painted with conductive silver ink which is used as reference electrode. This device was compared with a conventional glass electrode, and the results presented linear behavior in the pH range from 2.0 to 12.5, in Na⁺ and K⁺ solutions, exceeding glass electrodes in the alkaline range. The sensitivity was 56.9 ± 0.2 mV pH^? 1 and using ANOVA test we conclude that the electrode is not sensitive to the presence of alkaline cations such as Li⁺, Na⁺ or K⁺. Finally, the response time (t₉₅) was 4.9 to 9.0 s depending on the solution pH. The combined pH microelectrode can be used several times and, after three years, continues to have a response similar to that of a freshly produced one.     

Low potential detection of nicotine at multiwalled carbon nanotube–alumina-coated silica nanocomposite

Electrocatalytic oxidation of nicotine at multiwalled carbon nanotube (MWCNT)–alumina-coated silica (ACS) nanocomposite modified glassy carbon electrode are described. The sensing performance of the MWCNT–ACS nanocomposite modified glassy carbon electrode for the electrooxidation of nicotine was investigated using cyclic voltammetry and amperometry in 0.1 M phosphate buffer solution (pH 8). The MWCNT–ACS nanocomposite modified glassy carbon electrode exhibited the abilities to decrease the electrooxidation potential, to prevent the electrode surface fouling, and to raise the current responses. The MWCNT–ACS nanocomposite responded rapidly to nicotine with a sensitivity of 1.786 A M^?1 cm^?2 and a detection limit of 1.42 μM (according to 3σ criterion). A signal almost 180 times more sensitive was obtained at MWCNT–ACS nanocomposite modified glassy carbon electrodes as compared to bare glassy carbon electrode. The nicotine oxidation potential obtained in this study is much lower than that at boron-doped diamond electrodes.     

Electrooxidation of insulin at silicon carbide nanoparticles modified glassy carbon electrode

For the first time silicon carbide nanoparticles (SiC) was used for electrode modification and electrocatalytic oxidation of insulin. In comparison to bare glassy carbon (GC) electrode, the oxidation of insulin at GC electrode modified with SiC nanoparticles occurred at reduced overpotentials. The modified electrode was applied for insulin detection using cyclic voltammetry, differential pulse voltammetry (DPV) and flow injection analysis (FIA). Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range up to 600 pM, sensitivity of 710 pA pM^?1 cm^?2 and detection limit of 3.3 pM. In addition interference effect of the electroactive existing species (uric acid, glucose, lactic acid, l-cysteine and cholesterol) was diminished and for ascorbic acid eliminated by covering the surface of modified electrode with nafion film. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long term stability and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit and antifouling properties of this insulin sensor are better than all of the reports in the literature for insulin detection at physiological pH solutions.     

New analysis of clopidogrel bisulfate in plavix tablet and human biological fluids utilizing chemically modified carbon paste sensor

The fabrication and the performance response characteristics of a sensitive, selective, simple, and rapid sensor for the determination of clopidogrel bisulfate (CLO-H₂SO₄) were described. The constructed carbon paste sensor comprised of an ion-pair based on clopidogrel with silicotungstate (CLO-ST) where this study included: composition, usable pH range, response time and temperature. The sensor exhibited a wide linear dynamic concentration ranging from 1.00 × 10⁻⁷ to 1.00 × 10⁻² and the usable pH ranges from 1.2 to 4.8 with the response time ranging from 5 to 8 s which is much faster compared to liquid ISEs with a detection limit equalling 0.34 nM. The selectivity of the sensor (CLO-H₂SO₄) was applied with respect to many of organic and inorganic cations, amino acids and sugars. The sensor had applications in bulk powder, tablets, humans (serum-urine) and in monitoring Plavix tablets’ dissolution rates. The obtained results were statistically analyzed for both accuracy and precision and were compared using the US pharmacopeial method where no significant difference was observed.     

Highly selective thiocyanate electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) complex as neutral carrier

A novel selective thiocyanate PVC membrane electrode based on bis-bebzoin-semitriethylenetetraamine binuclear copper(II) [Cu(II)₂–BBSTA] as neutral carrier is reported, which displays an anti-Hofmeister selectivity sequence in following order: SCN⁻ > ClO₄⁻ > I⁻ >Sal⁻ >SO₃²⁻ >NO₃⁻ > H₂PO₄⁻ > Cl⁻ >NO₂⁻ > SO₄²⁻. The electrode exhibits Nernstian potential linear range to thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ mol/l with a detection limit 7.0 × 10⁻⁷ mol/l and a slope of −57.0 mV/decade in pH 5.0 of phosphorate buffer solution at 25 °C. The response mechanism is discussed in view of the AC impedance technique and the UV spectroscopy technique. From comparison of potentiometric response characteristics between the binuclear metallic complex copper(II) [Cu(II)₂–BBSTA] and mononuclear copper(II) metallic complex [Cu(II)–BBSDA], an enhanced response towards thiocyanate from the electrode based on binuclear metallic complex copper (II) [Cu(II)₂–BBSTA] was observed. The electrode based on binuclear copper(II) compound was used to determine the thiocyanate content in waste water with satisfactory results.     

Novel visible-light-responsive photoelectrochemical sensor of 2,4-dichlorophenoxyacetic acid using molecularly imprinted polymer/BiOI nanoflake arrays

A novel and highly sensitive visible-light photoelectrochemical (PEC) sensor for the detection of 2,4-D has been developed using a nanocomposite of molecularly imprinted gold nanoparticles-polypyrrole polymer (MIP) modified BiOI nanoflake arrays (BiOINFs) as a photoactive electrode (labeled as MIP@BiOINFs). Our results demonstrate that the smart combination of BiOINFs with MIP offers a high-performance photoactive sensing platform. It features the intrinsically excellent visible-light responsive properties of BiOI and prominent recognition ability from MIP. The designed MIP@BiOINF composite dramatically facilitates the PEC determination of 2,4-D. The detection limit for 2,4-D is found to be as low as about 0.04 ng mL^− 1 (S/N = 3). Moreover, the resulting sensor could be used to detect 2,4-D in spiked soil samples.     

Amperometric enzyme biosensor for hydrogen peroxide via Ugi multicomponent reaction

A novel strategy based on the Ugi multicomponent reaction was employed for immobilizing horseradish peroxidase on sodium alginate-coated gold electrode. The electrode was employed for constructing an amperometric biosensor device using 1 mM hydroquinone as electrochemical mediator. The electrode showed linear response (poised at −300 mV vs Ag/AgCl) toward H₂O₂ concentration between 70 μM and 8.8 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 12 s and its sensitivity was 33.8 mA/M cm². The electrode retained full initial activity after 30 days of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0.     

Determination of formal potential of NADH/NAD+ redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes

The electrochemical regeneration of NADH/NAD⁺ redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be ? 0.365 ± 0.002 V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2 M NaClO₄/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670 mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2 M H₂SO₄ solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 10³–10⁴ M^?1 s^? 1 depending on the preparation conditions of the PPS-modified electrodes.     

The process of immobilizing enzyme of glucose sensor based on diamond film

Considering the poor adhesion of electrode to substrate, diamond film as a new kind of substrate material was used to fabricate a glucose sensor. Particularly, the immobilizing enzyme was investigated in detail. SEM and XPS were chosen to identify whether organic functional groups were grafted to electrode surface or not. The response characteristics of a diamond film glucose sensor show that this glucose sensor has good properties in the linear range 0.5–11.4 mM l^-1, sensitivity 4.0 nA mM^-1 mm^-2 and peak reaction speed 2.5 μA. The glucose sensor based on diamond film was a novel microchip glucose sensor with good potential.