Liqiang Luo

Nonenzymatic amperometric determination of glucose by CuO nanocubes-graphene nanocomposite modified electrode

Here, we report a nonenzymatic amperometric glucose sensor based on copper oxide (CuO) nanocubes-graphene nanocomposite modified glassy carbon electrode (CuO-G-GCE). In this case, the graphene sheets were cast on the GCE directly. CuO nanocubes were obtained by oxidizing electrochemically deposited Cu on the graphene. The morphology of CuO-G nanocomposite was characterized by scanning electron microscopy. The CuO-G-GCE-based sensor exhibited excellent electrocatalytic activity and high stability for glucose oxidation. Under optimized conditions, the linearity between the current response and the glucose concentration was obtained in the range of 2μM to 4mM with a detection limit of 0.7μM (S/N=3), and a high sensitivity of 1360μAmM(-1)cm(-2). The proposed electrode showed a fast response time (less than 5s) and a good reproducibility. The as-made sensor was applied to determine the glucose levels in clinic human serum samples with satisfactory results. In addition, the effects of common interfering species, including ascorbic acid, uric acid, dopamine and other carbohydrates, on the amperometric response of the sensor were investigated and discussed in detail.

DNA electrochemical biosensor based on thionine-graphene nanocomposite

A novel protocol for development of DNA electrochemical biosensor based on thionine-graphene nanocomposite modified gold electrode was presented. The thionine-graphene nanocomposite layer with highly conductive property was characterized by scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An amino-substituted oligonucleotide probe was covalently grafted onto the surface of the thionine-graphene nanocomposite by the cross-linker glutaraldehyde. The hybridization reaction on the modified electrode was monitored by differential pulse voltammetry analysis using an electroactive intercalator daunomycin as the indicator. Under optimum conditions, the proposed biosensor exhibited high sensitivity and low detection limit for detecting complementary oligonucleotide. The complementary oligonucleotide could be quantified in a wide range of 1.0 × 10(-12) to 1.0 × 10(-7)M with a good linearity (R(2)=0.9976) and a low detection limit of 1.26 × 10(-13)M (S/N=3). In addition, the biosensor was highly selective to discriminate one-base or two-base mismatched sequences.

Poly-glutamic acid modified carbon nanotube-doped carbon paste electrode for sensitive detection of L-tryptophan

A novel poly-glutamic acid (PGA) film modified carbon paste electrode (CPE) incorporating carbon nanotubes (CNTs) was first prepared for the determination of l-tryptophan (l-Trp). Scanning electron microscopy and Fourier transform infrared spectroscopy were applied for characterization of the surface morphology of the modified electrodes and cyclic voltammetry was used to investigate the electrochemical properties of the proposed electrode towards the oxidation of l-Trp. Optimization of the experimental parameters was performed with regard to pH, ratio of CNTs, concentration of glutamic acid, electro-polymerization cycles, accumulation time and concentration of sodium dodecylbenzene sulfonate. The linearity between the oxidation peak current and the l-Trp concentration was obtained in the range of 5.0×10(-8) to 1.0×10(-4)M with a detection limit of 1.0×10(-8)M (S/N=3) and the sensitivity was calculated to be 1143.79μA∙mM(-1)∙cm(-2). In addition, the PGA modified CPE incorporating CNTs displayed high selectivity, good stability and reproducibility, making it suitable for the routine analysis of l-Trp in clinical use.

Nonenzymatic glucose sensor based on nickel(II)oxide/ordered mesoporous carbon modified glassy carbon electrode

A highly sensitive and selective nonenzymatic glucose sensor based on electrodepositing NiO nanoparticles on ordered mesoporous carbon (named as NiO/OMC) modified glassy carbon electrode (GCE) was constructed. The synthesized OMC was characterized by X-ray diffraction, and the morphology images of OMC nanoparticle and NiO/OMC nanocomposite were characterized by scanning electron microscope. Electrochemical behaviors of glucose at the NiO/OMC/GCE were investigated by cyclic voltammetry and amperometry, and the modified electrode showed excellent electrochemical activity toward the oxidation of glucose. At the optimum conditions, the calibration curve for glucose determination was linear in the range of 2-1000 μM with a fast response time (<2 s), and a high sensitivity of 834.8 μA mM(-1) cm(-2) and a low detection limit (S/N=3) of 0.65 μM were obtained. In addition, the proposed sensor was successfully applied to analyze glucose level in human blood serum samples.

Simultaneous determination of L-cysteine and L-tyrosine using Au-nanoparticles/poly-eriochrome black T film modified glassy carbon electrode

A novel Au-nanoparticles/poly-eriochrome black T film modified glassy carbon electrode (AuNPs/PEBT/GCE) was constructed for the simultaneous determination of l-cysteine (L-Cys) and l-tyrosine (L-Tyr) by differential pulse voltammetry. Fourier transform infrared spectra and electrochemical impedance spectroscopy indicate that the PEBT film was successfully polymerized on the surface of GCE and the film efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analytes and electrode. The scanning electron microscope image shows that the immobilized AuNPs were spherical in shape and enhanced the electrical conductivity of PEBT film. In addition, PEBT film increased the oxidation currents of analytes four times when compared to bare GCE, and the AuNPs separated the oxidation potentials of L-Cys and L-Tyr by 488 mV while bare GCE failed to resolve them. The amperometry results exhibit that the electrocatalytic currents increased linearly with L-Cys concentrations in the range 0.05-100 μM (r=0.9981), and the detection limits of L-Cys and L-Tyr were 8 nM and 10 nM (S/N=3), respectively. With high sensitivity and selectivity, the proposed electrochemical sensor provides a simple method for simultaneous determination of L-Cys and L-Tyr.

Synthesis of MnCo2O4 nanofibers by electrospinning and calcination: application for a highly sensitive non-enzymatic glucose sensor

Spinel-type MnCo2O4 nanofibers (MCFs) were successfully synthesized by electrospinning and sequential calcination. The crystal structure, composition and morphology of the synthesized MCFs were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Due to the outstanding electron-transfer ability of spinel MnCo2O4 and the large surface area of nanofibers, the synthesized MCFs were employed as electrocatalysts for the oxidation of glucose. Cyclic voltammetry and amperometry were used to evaluate the electrocatalytic activities of the MCFs towards glucose. The non-enzymatic glucose sensor showed a wide linear range of 0.05-800 μM with a low detection limit of 0.01 μM (S/N = 3).

Electrospun graphene decorated MnCo2O4 composite nanofibers for glucose biosensing

Graphene decorated MnCo2O4 composite nanofibers (GMCFs) were synthesized by electrospinning and subsequent calcination in an Ar atmosphere. The structural and morphological characterizations of GMCFs were performed using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, scanning electron microscopy and transmission electron microscopy. The synthesized GMCFs combine the catalytic activity of spinel-type MnCo2O4 with the remarkable conductivity of graphene. In addition, electrospinning can process MnCo2O4 materials into nanosized architectures with large surface area to prevent magnetic nanoparticles from aggregating. The obtained GMCFs were applied as a novel platform for glucose biosensing. Electrochemical studies show that the developed biosensor exhibits excellent electrocatalytic activity towards glucose oxidation over a wide linear range of 0.005-800µM with a low detection limit of 0.001µM.

Synthesis of hollow copper oxide by electrospinning and its application as a nonenzymatic hydrogen peroxide sensor

Cupric acetate/polyacrylonitrile composite nanofibers were prepared by electrospinning and hollow copper oxide (CuO) particles were produced after subsequent thermal treatment process. The electrospun hollow CuO particles modified carbon paste electrode (CPE) was demonstrated for the first time for nonenzymatic hydrogen peroxide (H(2)O(2)) sensor. The structures and morphologies of hollow CuO particles were characterized by scanning electron microscopy and X-ray diffraction spectrum. The assay performance of the modified sensor to H(2)O(2) was evaluated by cyclic voltammetry and amperometry, revealing high sensitivity (1746.50 μA mM(-1) cm(-2)), low detection limit (0.022 μM) and wide linear response of determination of H(2)O(2) oxidation in the range of 0.05 μM to 1.00 mM.

A novel nonenzymatic hydrogen peroxide sensor based on LaNi0.5Ti0.5O3/CoFe2O4 modified electrode

A novel nonenzymatic hydrogen peroxide (H(2)O(2)) sensor based on LaNi(0.5)Ti(0.5)O(3)/CoFe(2)O(4) nanoparticles modified glassy carbon electrode (LNT-CFO/GCE) was proposed. Perovskite-type nanocomposite oxide LaNi(0.5)Ti(0.5)O(3)/CoFe(2)O(4) was synthesized by sol-gel method and characterized by X-ray diffraction and transmission electron microscopy. The electrochemical properties of the modified electrode were studied by cyclic voltammetry and amperometry, which showed an excellent electrocatalytic activity for the oxidation of H(2)O(2). Under the optimum conditions, the linear response was obtained in the range of 0.1 μM to 8.2 mM, with the correlation coefficient of 0.997. The sensitivity of the modified electrode was calculated to be 3.21 μA μM(-1) cm(-2) and the detection limit was 23 nM (based on the S/N=3).

Electrochemical determination of nitrobenzene using bismuth -film modified carbon paste electrode in the presence of cetyltrimethylammonium bromide

Electrochemical behavior of nitrobenzene (NB) at a bismuth-film modified carbon paste electrode (BiF/CPE) in the presence of cetyltrimethylammonium bromide (CTAB) was investigated by square wave voltammetry. The electrochemical response of NB was apparently improved by CTAB due to the enhanced accumulation of NB at the electrode surface. Operational parameters including the deposition potential and time of bismuth film, pH of solutions and concentration of CTAB were investigated and optimized. Under optimized conditions, the cathodic peak current was proportional to the concentration of NB in the range of 1.0 × 10−6 to 1.0 × 10−4 mol L−1 with the detection limit of 8.3 × 10−7 mol L−1. The proposed BiF/CPE revealed good stability and reproducibility for rapid, simple and sensitive analysis of NB.