Haoqing Hou

Simultaneous electrochemical determination of dopamine, uric acid and ascorbic acid using palladium nanoparticle-loaded carbon nanofibers modified electrode

Palladium nanoparticle-loaded carbon nanofibers (Pd/CNFs) were prepared by electrospinning and subsequent thermal treatment processes. Pd/CNFs modified carbon paste electrode (Pd/CNF-CPE) displayed excellent electrochemical catalytic activities towards dopamine (DA), uric acid (UA) and ascorbic acid (AA). The oxidation overpotentials of DA, UA and AA were decreased significantly compared with those obtained at the bare CPE. Differential pulse voltammetry was used for the simultaneous determination of DA, UA and AA in their ternary mixture. The peak separation between UA and DA, DA and AA was 148 mV and 244 mV, respectively. The calibration curves for DA, UA and AA were obtained in the range of 0.5-160 microM, 2-200 microM, and 0.05-4mM, respectively. The lowest detection limits (S/N=3) were 0.2 microM, 0.7 microM and 15 microM for DA, UA and AA, respectively. With good selectively and sensitivity, the present method was applied to the determination of DA in injectable medicine and UA in urine sample.

Nonenzymatic glucose sensor based on renewable electrospun Ni nanoparticle-loaded carbon nanofiber paste electrode

A novel nonenzymatic glucose sensor was developed based on the renewable Ni nanoparticle-loaded carbon nanofiber paste (NiCFP) electrode. The NiCF nanocomposite was prepared by combination of electrospinning technique with thermal treatment method. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that large amounts of spherical nanoparticles were well dispersed on the surface or embedded in the carbon nanofibers. And the nanoparticles were composed of Ni and NiO, as revealed by energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD). In application to nonenzymatic glucose determination, the renewable NiCFP electrodes, which were constructed by simply mixing the electrospun nanocomposite with mineral oil, exhibited strong and fast amperometric response without being poisoned by chloride ions. Low detection limit of 1 microM with wide linear range from 2 microM to 2.5 mM (R=0.9997) could be obtained. The current response of the proposed glucose sensor was highly sensitive and stable, attributing to the electrocatalytic performance of the firmly embedded Ni nanoparticles as well as the chemical inertness of the carbon-based electrode. The good analytical performance, low cost and straightforward preparation method made this novel electrode material promising for the development of effective glucose sensor.

Electrochemical determination of L-Tryptophan, L-Tyrosine and L-Cysteine using electrospun carbon nanofibers modified electrode

A novel and simple method for the direct and quantitative determination of L-tryptophan (Trp), L-tyrosine (Tyr) and L-cysteine (Cys) was proposed in this work. Carbon nanofibers (CNFs), made by electrospinning technique, were used to modify carbon paste electrode (CPE) without any treatment to study the electrochemical behaviors of the three amino acids using cyclic voltammetry (CV) and constant potential amperometric method. The results demonstrated that the CNFs modified carbon paste electrode (CNF-CPE) exhibited high electrocatalytic activity and good analytical performance towards the oxidation of the three amino acids. The linear ranges of Trp, Tyr and Cys were 0.1-119, 0.2-107 and 0.15-64 microM with correlation coefficients of 0.9994, 0.9985 and 0.9996, respectively. All the detection limits of the analytes were 0.1 mM (S/N=3). In addition, the CNF-CPE displayed good reproducibility, high sensitivity and good selectivity towards the determination of the amino acids, making it suitable for the determination of Trp, Tyr and Cys in clinical and medicine.

A novel and simple route to prepare a Pt nanoparticle-loaded carbon nanofiber electrode for hydrogen peroxide sensing

A facile wet-chemical method was developed to prepare a novel Pt nanoparticle-loaded carbon nanofiber (Pt/CNF) electrode. Without using any stabilizer or pretreatment procedure, large amounts of Pt nanoparticles could be well deposited on the surface of the electrospun CNF electrode at room temperature, as revealed by scanning electron microscopy (SEM). The effect of the precursor concentration on the formation of Pt catalysts was investigated to optimize the performance of the proposed hybrid electrode. When applied to the electrochemical detection of hydrogen peroxide (H₂O₂), the Pt/CNF electrode exhibited low overpotential, fast response and high sensitivity. A low detection limit of 0.6 μM with wide linear range of 1-800 μM (R=0.9991) was achieved at the Pt/CNF electrode, which was superior to that obtained with other H₂O₂ electrochemical sensors reported previously. In addition, the Pt/CNF electrode showed good selectivity for H₂O₂ detection in the presence of ascorbic acid (AA), acetaminophenol (AP) and uric acid (UA) under physiological pH condition. The attractive analytical performances and facile preparation method made this novel hybrid electrode promising for the development of effective H₂O₂ sensors.

Enzyme-free ethanol sensor based on electrospun nickel nanoparticle-loaded carbon fiber paste electrode.

We have developed a novel nickel nanoparticle-loaded carbon fiber paste (NiCFP) electrode for enzyme-free determination of ethanol. An electrospinning technique was used to prepare the NiCF composite with large amounts of spherical nanoparticles firmly embedded in carbon fibers (CF). In application to electroanalysis of ethanol, the NiCFP electrode exhibited high amperometric response and good operational stability. The calibration curve was linear up to 87.5 mM with a detection limit of 0.25 mM, which is superior to that obtained with other transition metal based electrodes. For detection of ethanol present in liquor samples, the values obtained with the NiCFP electrode were in agreement with the ones declared on the label. The attractive analytical performance and simple preparation method make this novel material promising for the development of effective enzyme-free sensors.

A novel hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide/cysteamine-modified gold electrode

A novel strategy to fabricate a hydrogen peroxide sensor based on Ag nanoparticles electrodeposited on chitosan-graphene oxide nanocomposites/cysteamine-modified gold (Au) electrode was reported. The chitosan-graphene oxide nanocomposites were first assembled on a cysteamine-modified Au electrode to produce chitosan-graphene oxide/cysteamine/Au electrode. Then Ag nanoparticles were electrodeposited on the modified Au electrode and formed Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The chitosan-graphene oxide nanocomposites and the electrodeposited Ag nanoparticles were characterized by atomic force microscopy and scanning electron microscopy. The results showed the Ag nanoparticles were uniformly dispersed on the chitosan-graphene oxide/cysteamine/Au electrode. The cyclic voltammagrams and amperometric method were used to evaluate electrocatalytic properties of the Ag nanoparticles/chitosan-graphene oxide/cysteamine/Au electrode. The results showed that the modified electrode displayed good electrocatalytic activity to the reduction of hydrogen peroxide with a detection limit of 0.7xa0μM hydrogen peroxide based on a signal-to-noise ratio of 3. The sensor has good reproducibility, wide linear range, and long-term stability.

A nonenzymatic sensor for xanthine based on electrospun carbon nanofibers modified electrode

Xanthine (Xa) determination is of considerable importance in clinical analysis and food quality control. Therefore, a sensitive nonenzymatic amperometric sensor for Xa based on carbon nanofibers (CNFs) has been proposed. The CNFs, which were prepared by electrospinning technique and subsequent thermal treatment, were used to modify carbon paste electrode (CNF-CPE) to construct the amperometric sensor device without any oxidation pretreatment. In application to Xa electrochemical determination, the CNF-CPE exhibited high electrocatalytic activity and fast amperometric response. Various experimental parameters, such as pH and applied potential were optimized. Under the optimal conditions, the dynamic linear range of Xa was 0.03-21.19 μM (R=0.9992) with the detection limit low to 20 nM (S/N=3). With good selectivity and sensitivity, the present system was successfully applied to estimate the freshness of fish and determine Xa in human urine, which provides potential application in food quality control and clinical analysis.

Electrochemical determination of oxalic acid using palladium nanoparticle-loaded carbon nanofiber modified electrode

We have developed a novel electrochemical oxalic acid (OA) sensor based on the palladium nanoparticle-loaded carbon nanofiber (Pd/CNF) composites. These composites with large amounts of spherical nanoparticles well dispersed on the carbon nanofibers (CNF) were produced by combination of electrospinning technique with thermal treatment method. When applied to oxidation of OA, the Pd/CNF modified carbon paste electrode (Pd/CNF-CPE) exhibited high electrocatalytic performances with fast voltammetric responses and notably decreased overpotential compared to the bare and even the CNF modified CPE. A detection limit of 0.2 mM with linear ranges of 0.2–13 mM and 13–45 mM can be obtained at the Pd/CNF-CPE. Based on its high sensitivity and good selectivity, the proposed method was applied to determination of OA in spinach, and the satisfactory results confirmed the applicability of this sensor in practical analysis.

Electron transfer and electrocatalytics of cytochrome c and horseradish peroxidase on DNA modified electrode.

A bio-interphase composed of DNA, cytochrome c (Cyt c) and horseradish peroxidase (HRP) was developed by layer-by-layer assembling Cyt c, DNA and Cyt c-HRP on biocompatible 11-mercaptoundecanoic acid--6-mercapto-1-hexanol modified gold electrode. The new bio-interphase was used as a model system to mimic the electron transfer and electrocatalytic performance of two proteins in living organisms. Results showed that the electron transfer rate at bi-protein bio-interphase was faster than those at the single protein bio-interphase, indicating a synergistic interaction between the two proteins occurred in the electron transfer. Moreover, the mixed proteins modified electrode exhibited good electrocatalytic response to reduction of hydrogen peroxide (H₂O₂) and oxygen (O₂), suggesting that it could be used as a sensor for H₂O₂ and O₂ detection. The properties of the bio-interphase, together with the bioelectrocatalytic activity, could make it useful in the development of bioelectronic devices, and investigation of electrochemistry of other heme proteins at functional interphase. It would also provide a new strategy for further study on the electron transfer of other multi-proteins in a bio-interphase and the development of biosensors.

Scanning Tunneling Microscopy Study of α,ω-Dihexylsexithiophene Adlayers on Au(111): A Chiral Separation Induced by a Surface

The self-assembly of α,ω-dihexylsexithiophene molecules on an Au(111) surface was examined by using scanning tunneling microscopy at room temperature, revealing the internal molecular structures of the sexithiophene backbones and the hexyl side chains. The α,ω-dihexylsexithiophene formed a large and well-ordered monolayer in which the molecule lay flatly on the Au(111) surface and was separated into two chiral domains. A detailed observation reveals that the admolecules were packed in one lamellae with their molecular axis aligned along the main axis of the Au(111) substrate with their hexyl chains deviated from <110> direction of the Au(111) substrate by 12 ± 0.5°. In contrast to the behavior in the three-dimensional bulk structure, flat-lying adsorption introduced molecular chirality: right- and left-handed molecules separate into domains of two different orientations, which are mirror symmetric with respect to the <121> direction of the Au(111) substrate. Details of the adlayer structure and the chiral self-assembly were discussed here.