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.     

A glucose/O2 biofuel cell base on nanographene platelet-modified electrodes

This study demonstrated a novel nanographene platelets (NGPs)-based glucose/O₂ biofuel cell (BFC) with the glucose oxidase (GOD) as the anodic biocatalysts and the laccase as the cathodic biocatalysts. The GOD/NGPs-modified electrode exhibited good catalytic activity towards glucose oxidation and the laccase/NGPs-modified electrode exhibited good catalytic activity towards O₂ electroreduction. The maximum power density was ca. 57.8 μW cm^? 2 for the assembled glucose/O₂ NGPs-based BFC. These results indicated that the NGPs were very useful for the future development of novel carbon-based nanomaterials BFC device.     

Gold nanoparticles integrated in a nanotube array for electrochemical detection of glucose

An enzyme-free amperometric glucose sensor of gold nanoparticle-constituted nanotube array electrode is presented. The resulted gold nanotube array electrode with significantly enhanced surface roughness shows prominent catalytic activity toward the electrooxidation of glucose in a pH 7.4 phosphate buffer (PBS) solution and thus can be used to individually or simultaneously determine glucose and the common interfering molecule of ascorbic acid (AA). In the case of glucose detection, the amperometric responses show a linear relationship to glucose concentration in the range of 1 mM–42.5 mM with a detection limit down to 10 μM. The present non-enzymatic glucose electrochemical biosensor shows a good stability and reproducibility.     

Ferrocene-modified Fe3O4@SiO2 magnetic nanoparticles as building blocks for construction of reagentless enzyme-based biosensors

A novel amperometric glucose biosensor was developed by entrapping glucose oxidase (GOD) in chitosan (CS) composite doped with ferrocene monocarboxylic acid-modified magnetic core-shell Fe₃O₄@SiO₂ nanoparticles (FMC-AFSNPs). It is shown that the obtained magnetic bio-nanoparticles attached to the surface of a carbon paste electrode (CPE) with the employment of a permanent magnet showed excellent electrochemical characteristics and at the same time acted as mediator to transfer electrons between the enzyme and the electrode. Under optimal conditions, this biosensor was able to detect glucose in the linear range from 1.0 × 10⁻⁵ to 4.0 × 10⁻³ M with a detection limit of 3.2 μM (S/N = 3). This immobilization approach effectively improved the stability of the electron transfer mediator and is promising for construction of biosensor and bioelectronic devices.     

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.     

Functionalization of multi-walled carbon nanotubes with poly(amidoamine) dendrimer for mediator-free glucose biosensor

By grafting with poly(amidoamine) (PAMAM) dendrimer, novel carbon nanotube (CNT) nano-composites have been successfully prepared. The novel functionalized matrix with plenty amino groups circumvents the troublesome solubility problem of CNTs in solvents, especially in water, greatly expanding the scope of the application of carbon nanotubes. The GO_x and HRP immobilized CNT-PAMAM based on the functional CNTs was synthesized. The bi-enzymatic CNT-PAMAM nano-composites are highly dispersible in water and show very promising applications in the fabrication of mediator-free bi-enzymatic biosensors for sensitive detection of glucose. The cooperation of nano-composite between CNT and high dense GO_x and HRP results in very high sensitivity to glucose with a current response of 2200 nA mM⁻¹ and fast response (∼1 s). The modified electrode exhibits a wide linear response range for glucose from 4.0 μM to 1.2 mM (R = 0.9971, N = 15), with a detection limit of 2.5 μM. The negative electrode potential of −0.34 V is favorable for glucose detection in real samples without interference caused by other biomolecules.     

Enhancement of the performances of a single concentric glucose/O2 biofuel cell by combination of bilirubin oxidase/Nafion cathode and Au–Pt anode

This work deals with a novel preparation method of bilirubin oxidase/2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid electrode. The enzyme and its mediator were adsorbed on carbon Vulcan XC-72R before their immobilization into a Nafion^® matrix. Promising results were obtained when this biocathode was associated with Au₇₀Pt₃₀ nanoparticles as anode in a single concentric glucose/O₂ biofuel cell (BFC). The latter BFC delivered at 37 °C a power density of 90 μW cm^?2 for a cell voltage of 0.4 V in phosphate buffer (pH 7.4) containing 0.01 M glucose. Moreover, the electrical performances were increased with the concentration of glucose by generating up to 190 μW cm^?2 for a cell voltage of 0.52 V when the concentration of the renewable fuel reached 0.7 M.     

Gold nanoparticles/tetraaminophenyl porphyrin functionalized multiwalled carbon nanotubes nanocomposites modified glassy carbon electrode for the simultaneous determination of p-acetaminophen and p-aminophenol

A novel electrochemical platform was designed and prepared for simultaneous determination of p-acetaminophen (AMP) and p-aminophenol (AP) by combining the excellent conductivity and electrocatalytic activities of tetraaminophenyl porphyrin functionalized multi-walled carbon nanotubes (CNTs-CONH-TAPP) and gold nanoparticles (AuNPs). The as-synthesized CNTs-CONH-TAPP composites were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscope. The incisive oxidation current responses of AMP and AP at the modified electrode promised a sensitive and selective simultaneous determination of AMP and AP. Under optimized conditions, the peak currents were directly proportional to the concentrations of AMP and AP over the ranges of 4.5–500 μmol L⁻¹ and 0.08–60 μmol L⁻¹, respectively, and the limits of detection were 0.44 μmol L⁻¹ for AMP and 0.025 μmol L⁻¹ for AP(S/N = 3) respectively. The proposed modified electrode showed excellent selectivity, reproducibility and long-term stability and could be applied in simultaneous determination of p-acetaminophen and p-aminophenol in real samples.     

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.     

Electrochemical stripping analysis of cadmium on tantalum electrode

A tantalum electrode is reported as an alternative electrode for electrochemical stripping analysis for the first time. Several key operational parameters that influenced the electroanalytical signals were optimized, such as pH of the electrolyte, deposition potential and deposition time. The tantalum electrode yields well-defined and sharp stripping signals for trace cadmium analysis when combined with differential pulse anodic stripping voltammetry. Under the optimized condition the electrode shows good linear behavior in the examined concentration in the range of 20–200 μg L^?1 for cadmium, with a detection limit (3σ) of 0.57 μg L^?1 followed a 5-min deposition step under ? 1.3 V. It also shows good reproducibility with a relative standard deviation of 2.56% for ten consecutive measurements. The sensor was also employed for real sample determination and exhibited excellent performance compared with the result of inductively coupled plasma-mass spectrometry.     

Porous cuprous oxide microcubes for non-enzymatic amperometric hydrogen peroxide and glucose sensing

Using porous cuprous oxide (Cu₂O) microcubes, a simple non-enzymatic amperometric sensor for the detection of H₂O₂ and glucose has been fabricated. Cyclic voltammetry (CV) revealed that porous Cu₂O microcubes exhibited a direct electrocatalytic activity for the reduction of H₂O₂ in phosphate buffer solution and the oxidation of glucose in an alkaline medium. The non-enzymatic amperometric sensor used in the detection of H₂O₂ with detection limit of 1.5 × 10^?6 M over wide linear detection ranges up to 1.5 mM and with a high sensitivity of 50.6 μA/mM. This non-enzymatic voltammetric sensor was further utilized in detection of glucose with a detection limit of 8.0 × 10^?7 M, a linear detection range up to 500 μM and with a sensitivity of ?70.8 μA/mM.     

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.     

Determination of tannic acid by adsorptive anodic stripping voltammetry at porous pseudo-carbon paste electrode

A novel and sensitive electrochemical sensor based on porous pseudo-carbon paste electrode (PPCPE) for tannic acid detection is described. PPCPE is fabricated by mixing calcium carbonate microspheres as the template, graphite powders as the filler, and pyrrole as the precursor of polymer which actually acted as the paste. After the polymerization of pyrrole catalyzed by Fe³⁺, the template calcium carbonate microspheres are removed with 0.1 M hydrochloric acid to form PPCPE. The diameters of these pores are in the range from 2 to 5 μm by SEM observations and the specific surface area of PPCPE is 59.26 m²/g by the Brunauer–Emmet–Teller (BET) method. A linear relationship between the anodic stripping peak current and the concentration of tannic acid from 0.02 to 1 μM and a limit of detection as low as 0.01 μM are obtained using PPCPE.     

Electrodeposition of PtCo alloy nanoparticles on inclusion complex film of functionalized cyclodextrin–ionic liquid and their application in glucose sensing

Platinum–cobalt (PtCo) alloy nanoparticles (NPs) are successfully fabricated by ultrasonic-electrodeposition method, using an inclusion complex (IC) film of functionalized cyclodextrin (CD)–ionic liquid (IL) as support. The morphology and composition of the PtCo alloy NPs are characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. It is found that they are well-dispersed on the CD–IL surface and exhibit many unique features. The resulting modified glassy carbon electrode shows excellent catalytic activity for glucose oxidation. Under the physiological condition, the oxidation current of glucose is linear to its concentration up to 20 mM with sensitivity of 13.7 μA mM^?1 cm^?2. In addition, the interference from the oxidation of ascorbic acid and uric acid could be effectively avoided. Therefore, it is promising as a nonenzymatic glucose sensor.     

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.     

Direct determination of arsenate based on its electrocatalytic reduction at the poly(aniline-co-o-aminophenol) electrode

It was found that the copolymer poly(aniline-co-o-aminophenol) (PANOA) can strongly catalyze the reduction of arsenate in a NaCl solution, which was proved by cyclic voltammetry and the determination of activation energy. On the basis of the electrocatalytic reduction of arsenate, the PANOA copolymer was used as a probe to determine directly arsenate. The electrocatalytic activity of the PANOA electrode toward As(V) reduction strongly depended on the pH and the applied potential. Under the optimal conditions, the PANOA electrode can be used to determine directly As(V) concentration in a wide linear range (n = 19) of 0.949 and 495 μM with a correlation coefficient of 0.995 and a limit of detection of 0.495 μM. The sensitivity of the electrode was 0.192 μA μM^?1 cm^?2. The PANOA electrode had the good storage stability and a less negative operation potential of ?0.15 V (vs. SCE).     

Study of ITO Glass Electrode Modified with Iron Oxide Nanoparticles and Nafion for Glucose Biosensor Application

In this study, we report the fabrication of the indium tin oxide (ITO) glass electrode modified with iron oxide nanoparticles (IONPs) and nafion for glucose biosensor applications. The IONPs was synthesized using the precipitation method and functionalized with citric acid (CA) to provide hydrophilic surface and functional group for glucose oxidase (GOx) enzyme immobilization. The structural and morphological studies of CA-IONPs were characterized using X-ray diffractometer (XRD) and transmission electron microscope (TEM). The size of the IONPs measured from TEM image was ∼17 nm. The bioelectrode designated as Nafion/GOx/CA-IONPs/ITO was developed by drop casting of the CA-IONPs, GOx and nafion on the ITO glass. The Nafion/GOx/CA-IONPs/ITO bioelectrode showed good electrochemical performance for glucose detection. The functionalized CA-IONPs acted as the catalyst and help to improve the electron transfer rate between GOx and ITO electrode. In addition, thin nafion film was coated on the electrode to prevent interference and improve chemical stability. The Nafion/GOx/CA-IONPs/ITO bioelectrode showed high sensitivity of 70.1 μAmM^-1cm^-2 for the linear range of 1.0-8.0 mM glucose concentrations.     

An electrically heated ionic-liquid/multi-wall carbon nanotube composite electrode and its application to electrochemiluminescent detection of ascorbic acid

A heated composite electrode consisted of multi-wall carbon nanotube (MWNT) and ionic liquids (ILs) was designed and fabricated. The non-conductive binders were replaced by a conductive IL, n-octylpyridinum hexafluorophosphate (OPFP). This heated OPFP/MWNT composite electrode was applied for electrochemiluminescent (ECL) sensor, and the performance of ECL sensor was evaluated by ascorbic acid (AA)/lucigenin ECL system. The new heated electrode combines the advantages of ILs/CNT and heated electrode, showing high thermal stability and conductivity, simple heating setups, improved reproducibility, renewable surface, simplicity of fabrication and enhanced sensitivity with detection limit (S/N = 3) of 0.01 μmol/L for AA.     

Immobilization of biotinylated biomolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)–Cu2+ film

A novel and simple immobilization strategy for biotinylated biological macromolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)(NTA)–Cu²⁺ films without avidin as connecting bridge is reported. After complexation of Cu²⁺ by the polymerized NTA chelator, biotinylated biomolecules were immobilized by coordination of the biotin groups on the NTA–Cu²⁺ complex. The anchoring of biotinylated glucose oxidase was demonstrated by fluorescent characterization via FITC-labeled avidin and amperometric measurement of glucose. The resulting calibration curve led to a sensitivity and maximum current density values of 0.6 mA mol^?1 L cm^? 2 and 13.2 μA cm^? 2, respectively. Thus, biotinylated polyphenol oxidase was fixed leading to a catechol sensor with a sensitivity of 656 mA mol^?1 L cm^? 2 and maximum current density of 25.4 μA cm^? 2. This system was also applied to the efficient immobilization of biotinylated DNA, illustrated by impedimetric detection of the formation of the DNA duplex.     

A novel nitrogen-doped graphene fiber microelectrode with ultrahigh sensitivity for the detection of dopamine

A novel nitrogen doped graphene fiber (NGF) was fabricated via a simple and facile wet-spinning strategy followed by annealing at high temperature, which can be applied as a remarkable electrode material. The NGF microelectrode shows good sensitivity and selectivity for the detection of dopamine with a wide linear response in the range of 0.1 μM to 80 μM, with the detection limit of 30 nM and an ultrahigh sensitivity of 22.08 μA μM^− 1 cm^− 2. Such high performance enables the NGF to be a prominent material in the branch of electrochemical analysis.