A low-potential, H2O2-assisted electrodeposition of cobalt oxide/hydroxide nanostructures onto vertically-aligned multi-walled carbon nanotube arrays for glucose sensing

Electrophoretic Deposition of Co3O4 Particles/Reduced Graphene Oxide Composites for Efficient Non-Enzymatic H2O2 Sensing

In this work, the facile fabrication of Co₃O₄ particles/reduced graphene oxide (Co₃O₄/rGO) composites on Indium tin oxide (ITO) slide was achieved by an electrophoretic deposition and annealing process. The deposition time and ratio of the precursors were optimized. Structural characterization and chemical composition investigation indicated successful loading of Co₃O₄ particles on graphene sheets. When applied as a non-enzymatic H₂O₂ sensor, Co₃O₄/rGO showed significant electrocatalytic activity, with a wide linear range (0.1-19.5 mM) and high sensitivity (0.2247 mA mM^-1 cm^-2). The good anti-interference ability, reproducibility, and long-term stability of the constructed sensor were also presented. The application of Co₃O₄/rGO in real sample analysis was evaluated in human urine sample with satisfactory results, indicating the feasibility of the sensor in physiological and medical applications.

Determination of hydrogen peroxide released from cancer cells by a Fe-Organic framework/horseradish peroxidase-modified electrode

Multi-walled carbon nanotubes (MWCNTs) were used as conductive carrier on the glassy carbon electrode (GCE), and the hybrid of metal organic framework [NH₂-MIL-53(Fe)] and horseradish peroxidase (HRP) was prepared by simple physical mechanical mixture. The GCE modified by the above material with immobilization, namely NH₂-MIL-53(Fe)/HRP/MWCNTs/GCE, was used to construct an electrochemical biosensor toward H₂O₂. The results indicated that the addition of NH₂-MIL-53(Fe) had a good synergistic effect on the electron transfer of HRP and the detection of H₂O₂. Under the optimized condition, the biosensor exhibited excellent electrochemical performances such as low detection limit, high sensitivity, good stability and so on. The H₂O₂ biosensor showed two linear ranges of 0.1-1 μM and 1-600 μM with a calculated detection limit of 0.028 μM (signal-to-noise ratio, S/N = 3). In addition, the stability of the hybrid of NH₂-MIL-53(Fe) and HRP were discussed by SEM, XRD and UV-vis methods. Furthermore, the reported biosensors were practically used in direct detection of H₂O₂ released from HeLa and HepG2 cells successfully. Thus, this work provides a new strategy to fabricate electrochemical biosensors using MOFs and biomolecules.

Simultaneous voltammetric determination of cadmium(II), lead(II), mercury(II), zinc(II), and copper(II) using a glassy carbon electrode modified with magnetite (Fe3O4) nanoparticles and fluorinated multiwalled carbon nanotubes

A method is described for the simultaneous voltammetric determination of the heavy metal ions cadmium(II), lead(II), mercury(II), zinc(II), and copper(II) using a glassy carbon electrode (GCE) modified with magnetite (Fe3O4) nanoparticles and fluorinated multiwalled carbon nanotubes (Fe3O4/F-MWCNTs). The Fe3O4/F-MWCNT composite was synthesized by a hydrothermal method and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, elemental mapping, electrochemical impedance spectroscopy, and square wave stripping voltammetry. Under the optimum conditions, the electrode displays excellent response to the ions. Figures of merit for Cd(II), Pb(II), Hg(II), Zn(II), and Cu(II), respectively, include (a) high electrochemical sensitivity (29.88, 43.50, 120.86, 47.34 and 90.31 (μA μM-1 cm-2), (b) well separated peaks (at -0.70, -0.53, +0.37, -1.11 and + 0.01 V vs. Ag/AgCl); (c) low limits of detection (0.014, 0.0084, 0.0039, 0.012, and 0.0053 μM); and (d) wide linear ranges (0.048-30.0, 0.028-30.0, 0.013-32.5, 0.039-32.5, and 0.017-31.5 μM). The modified GCE displays satisfying selectivity in the presence of potentially interfering other metal ions, stability for 30 days, and reproducibility of electrodes (with a relative standard deviation between 1.2 and 4.8% for n = 6). The modified GCE was applied to the determination of several heavy metal ions in (spiked) water and rice samples, and the results agreed well with data obtained by atomic fluorescence spectrometry or inductively coupled plasma-mass spectrometry. The dramatic performance probably result from the semi-ionic C-F bond on F-MWCNTs surface with a strong negative charge, the good electrical conductivity of the F-MWCNTs and Fe3O4, the synergistic interaction between Fe3O4 and F-MWCNTs, and the nafion conductive membrane improving the stability of the modified layer and enhanced cation adsorption. Graphical abstract An environmentally-friendly, low-cost, high-throughput Fe3O4/fluorinated multi-walled carbon nanotube composite (Fe3O4/F-MWCNTs) modified glassy carbon electrode is described. It was applied to simultaneous electrochemical determination of Cd(II), Pb(II), Hg(II), Zn(II), and Cu(II) by square wave stripping voltammetry.

A bioinspired ionic liquid tagged cobalt-salophen complex for nonenzymatic detection of glucose

The development of efficient and cost effective nonenzymatic biosensors with remarkable sensitivity, selectivity and stability for the detection of biomolecules, especially glucose is one of the major challenges in materials- and electrochemistry. Herein, we report the design and preparation of nonenzymatic biosensor based on an ionic liquid tagged cobalt-salophen metal complex (Co-salophen-IL) immobilized on electrochemically reduced graphene oxide (ERGO) for the detection of glucose via an electrochemical oxidation. The bioinspired Co-salophen-IL complex has been synthesized and immobilized on ERGO, which was previously deposited on a screen printed carbon electrode (SPE) to form the Co-salophen-IL/ERGO/SPE nonenzymatic biosensor. The electrochemical behaviour of this modified electrode was studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Notably, the Co-salophen-IL/ERGO/SPE biosensor exhibited excellent electrocatalytic activity towards glucose oxidation in 0.1M NaOH, based on which an amperometric sensor has been developed. The modified electrode has shown prominent performance towards glucose detection over a wide linear range from 0.2µM to 1.8mM with a detection limit and sensitivity of 0.79µM and 62µAmM^-1 respectively. The detection was carried out at 0.40V and such a less working potential excludes the interference from the coexisting oxidizable analytes. The role of Co-salophen, IL and ERGO in the electrocatalytic activity has been systematically investigated. Furthermore, the biosensor demonstrated high stability with good reproducibility.

NiO/SiC nanocomposite prepared by atomic layer deposition used as a novel electrocatalyst for nonenzymatic glucose sensing

NiO nanoparticles are deposited onto SiC particles by atomic layer deposition (ALD). The structure of the NiO/SiC hybrid material is investigated by inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The size of the NiO nanoparticles is flexible and can be adjusted by altering the cycle number of the NiO ALD. Electrochemical measurements illustrate that NiO/SiC prepared with 600 cycles for NiO ALD exhibits the highest glucose sensing ability in alkaline electrolytes with a low detection limit of 0.32 μM (S/N = 3), high sensitivity of 2.037 mA mM(-1) cm(-2), a linear detection range from approximately 4 μM to 7.5 mM, and good stability. Its sensitivity is about 6 times of that for commercial NiO nanoparticles and NiO/SiC nanocomposites prepared by a traditional incipient wetness impregnation method. It is revealed that the superior electrochemical ability of ALD NiO/SiC is ascribed to the strong interaction between NiO and the SiC substrate and the high dispersity of NiO nanoparticles on the SiC surface. These results suggest that ALD is an effective way to deposit NiO on SiC for nonenzymatic glucose sensing.

Electrodeposition of a 3D hierarchical porous flower-like cobalt–MWCNT nanocomposite electrode for non-enzymatic glucose sensing

A versatile and cost-effective electrodeposition technique was adopted to synthesize cobalt and cobalt–MWCNT nanocomposite electrodes and the fabricated cobalt–MWCNT material was successfully demonstrated as a non-enzymatic glucose sensor.

Ultrasensitive electrochemical assay of hydrogen peroxide and glucose based on PtNi alloy decorated MWCNTs

A electrochemical sensor based on PtNi/MWCNTs can detect hydrogen peroxide and glucose with wide linear range and high sensitivity.

Electrochemical sensing of glucose by carbon cloth-supported Co3O4/PbO2 core-shell nanorod arrays

A novel electrochemical sensor for the detection of glucose was constructed based on the use of Co3O4/PbO2 core-shell nanorod arrays as electrocatalysts. In this paper the Co3O4/PbO2 core-shell nanorod arrays grow directly on a flexible carbon cloth substrate by the combination of hydrothermal synthesis and electrochemical deposition methods. The as-prepared hierarchical nanocomposites show the structural characteristics of nanowire core and nanoparticle shell. The carbon cloth-supported Co3O4/PbO2 nanorod array electrode exhibits higher sensitivity (460.3 μA mM(-1)cm(-2) in the range from 5 μM to 1.2mM) and lower detection limit (0.31 μM (S/N=3)) than the carbon cloth-supported Co3O4 nanowire array electrode. Both the three-dimensional network of carbon cloth substrate and the hierarchical nanostructure of binary Co3O4/PbO2 composites make such an electrode have high electrocatalytic activity towards the glucose oxidation. Due to the excellent sensitivity, repeatability and anti-interference ability, the carbon cloth-supported Co3O4/PbO2 nanorod arrays will be the promising materials for fabricating practical non-enzymatic glucose sensors.

Indium tin oxide-coated glass modified with reduced graphene oxide sheets and gold nanoparticles as disposable working electrodes for dopamine sensing in meat samples

Sensitive, rapid, and accurate detection of dopamine (DA) at low cost is needed for clinical diagnostic and therapeutic purposes as well as to prevent illegal use of DA in animal feed. We employed a simple approach to synthesize reduced graphene oxide sheets (rGOS) and gold nanoparticles (AuNPs) at room temperature on indium tin oxide-coated glass (ITO) slides as disposable working electrodes for sensing DA. Graphene oxide (GO) was directly reduced on ITO to remove oxygenated species via a rapid and green process without using chemical reducing reagents. AuNPs were electrochemically deposited in situ on rGOS-ITO with fairly uniform density and size. The sensitivity of the AuNPs-rGOS-ITO sensor for DA detection is 62.7 μA mM(-1) cm(-2) with good selectivity against common electrochemically interfering species such as ascorbic acid (AA) and uric acid (UA), and the detection limit measured by differential pulse voltammetry (DPV), at a signal-noise ratio of 3, was 6.0 × 10(-8) M. The electrochemical catalysis of DA was proven to be a surface process with an electron transfer coefficient (α) of 0.478 and a rate constant (k(s)) of 1.456 s(-1). It correlates well with the conventional UV-vis spectrophotometric approach (R = 0.9973) but with more than thrice the dynamic range (up to 4.5 mM). The sensor also exhibited good stability and capability to detect DA in beef samples, and thus is a promising candidate for simple and inexpensive sub-nanomolar detection of DA, especially in the presence of UV-absorbing compounds.

Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film

Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co(2+) concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO(3))(2), possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L(-1). The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method.

3D graphene-cobalt oxide electrode for high-performance supercapacitor and enzymeless glucose detection

Using a simple hydrothermal procedure, cobalt oxide (Co(3)O(4)) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co(3)O(4) composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co(3)O(4) composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g(-1) at a current density of 10 A g(-1) with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM(-1) cm(-2) and a remarkable lower detection limit of <25 nM (S/N = 8.5).