Xibin Zhou

Simultaneous determination of ascorbic acid, dopamine and uric acid based on tryptophan functionalized graphene.

A new type of tryptophan-functionalized graphene nanocomposite (Trp-GR) was synthesized by utilizing a facile ultrasonic method via π-π conjugate action between graphene (GR) and tryptophan (Trp) molecule. The material as prepared had well dispersivity in water and better conductivity than pure GR. The surface morphology of Trp-GR was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The electrochemical behaviors of ascorbic acid (AA), dopamine (DA), and uric acid (UA) were investigated by cyclic voltammetry (CV) on the surface of Trp-GR. The separation of the oxidation peak potentials for AA-DA, DA-UA and UA-AA was about 182 mV, 125 mV and 307 mV, which allowed simultaneously determining AA, DA, and UA. Differential pulse voltammetery (DPV) was used for the determination of AA, DA, and UA in their mixture. Under optimum conditions, the linear response ranges for the determination of AA, DA, and UA were 0.2-12.9 mM, 0.5-110 μM, and 10-1000 μM, with the detection limits (S/N=3) of 10.09 μM, 0.29 μM and 1.24 μM, respectively. Furthermore, the modified electrode was investigated for real sample analysis.

A sensor based on the carbon nanotubes-ionic liquid composite for simultaneous determination of hydroquinone and catechol

MWNTs-IL-Gel/GCE, a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs) and ionic liquids (IL), was developed to serve as a sensor for simultaneous determination of Hydroquinone (HQ) and catechol (CC) in this paper. The modified GCE showed two well-defined redox waves for HQ and CC in both CV and DPV with a peak potential separation of ca. 0.1 V, which was large enough for simultaneous detection. The results revealed that the oxidation of HQ and CC with the enhancement of the redox peak current and the decrease of the peak-to-peak separation exhibit excellent electrocatalytic behaviors. A high sensitivity of 1.8×10(-7)M with detection limits of 6.7×10(-8)M and 6.0×10(-8)M (S/N=3) for HQ and CC were obtained. Moreover, the constants of apparent electron transfer rate of HQ and CC at MWNTs-IL-Gel/GCE were calculated as 7.402 s(-1) and 8.179 s(-1), respectively, and the adsorption quantity of HQ and CC was 1.408×10(-6) mol cm(-2) with chronocoulometry. The developed sensor can be applied to determinate directly of HQ and CC in aqueous solution.

Determination of malachite green in fish based on magnetic molecularly imprinted polymer extraction followed by electrochemiluminescence.

A novel procedure for selective extraction of malachite green (MG) from fish samples was set up by using magnetic molecularly imprinted polymers (MMIP) as the solid phase extraction material followed by electrochemiluminescence (ECL) determination. MMIP was prepared by using Fe3O4 magnetite as magnetic component, MG as template molecule, methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent. MMIP was characterized by SEM, TEM, FT-IR, VSM and XRD. Leucomalachite green (LMG) was oxidized in situ to MG by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). And then MMIP was successfully used to selectively enrich MG from fish samples. Adsorbed MG was desorbed and determined by ECL. Under the optimal conditions, calibration curve was good linear in the range of 0.29-290 μg/kg and the limit of detection (LOD) was 7.3 ng/kg (S/N=3). The recoveries of MMIP extraction were 77.1-101.2%. In addition, MMIP could be regenerated. To the best of our knowledge, MMIP coupling with ECL quenching of Ru(bpy)3(2+)/TPA for the determination of MG has not yet been developed.

A amperometric biosensor for hydrogen peroxide by adsorption of horseradish peroxidase onto single-walled carbon nanotubes

Development of a highly sensitive nanostructured electrochemical biosensor based on the integrated assembly of horseradish peroxidase (HRP) and single-walled carbon nanotubes (SWNTs) is described. In this study, we describe the use of a sodium cholate suspension-dialysis method to adsorb the horseradish peroxidase (HRP) onto single-walled carbon nanotubes (SWNTs). We demonstrate that HRP-SWNTs conjugates can be assembled into amperometric biosensors which L-cysteine were assembled on a gold electrode through the covalent bond of S-Au and was used as a substrate for the immobilization of enzymes. Direct electron transfer of HRP is realized at SWNTs, and both anodic and cathodic currents of the redox reaction at the l-cysteine-HRP-SWNTs-modified gold film upon electrocatalysis are amplified. Meanwhile, experimental results reveal that HRP is stably immobilized onto the SWNTs and maintains inherent enzymatic activity toward H(2)O(2). The modified electrode shows high sensitivity toward H(2)O(2). A linear response to hydrogen peroxide measurement is obtained over the range from 1.0×10(-12) to 1.0×10(-11)M and an amperometric detection limit of 2.1×10(-13)M due to its bioelectrocatalytic reduction based on direct electron transfer between gold electrode and the active site of the HRP. The biosensor displays excellent operational, storage stability and highly sensitive. The excellent performance validates the integrated assembly as an attractive sensing element for the development of a new hydrogen peroxide amperometric biosensor.

A simple and an efficient strategy to synthesize multi-component nanocomposites for biosensor applications.

We demonstrate that core-shell multi-component nanocomposites can be grown in situ at room temperature by a novel one-step approach without adding any reductant and stabilizer. We have presented a one-step method for the synthesis of multi-component nanocomposites in water solution, the multi-component nanocomposites could be produced directly and quickly in an in situ wet-chemical reaction. Here, Au-polypyrrole (PPy)/Prussian blue (PB) nanocomposites have been synthesized successfully under the same circumstance. With the addition of pyrrole monomers into mixture solutions, the autopolymerization of pyrrole into PPy and AuCl(4)(-) was reduced to elemental Au instantaneously as well as simultaneously. At the same time, PB produced along with elemental Au serving as a catalyst. Furthermore, we investigated the performance of Au-PPy/PB nanocomposites as amperometric sensor toward the reduction of H(2)O(2), which displayed high sensitivity, fast response and good stability. The peak current of H(2)O(2) increased linearly with the concentration of H(2)O(2) in the range from 2.5×10(-9) to 1.2×10(-6)M, and the low detection limit of 8.3×10(-10)M (S/N=3) was obtained. Therefore, this work provides a new pathway to design and fabricate novel multi-component nanocomposites, which have unique characteristics and hold great applications in the fields of sensors, electrocatalysis and others.

A novel electrochemical sensor for capsaicin based on mesoporous cellular foams

A novel electrochemical sensor for capsaicin using mesoporous cellular foams (MCFs) as the sensitive material is reported. The surface morphology and electrochemical properties of the prepared MCFs modified carbon paste electrode (CPE) were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed modified electrode shows high sensitivity towards the oxidation of capsaicin in 0.1 M perchloric acid solutions (pH 1.0). Under optimized conditions, the electrochemical oxidation current of capsaicin was found to be linearly related to the concentration over the range 0.76 to 11.65 μM with a correlation coefficient of 0.9990, and the detection limit was found to be 0.08 μM at a signal-to-noise ratio of 3. The proposed electrochemical sensor was successfully applied to the determination of capsaicin by using standard addition method with satisfactory results.

Quenching of the electrochemiluminescence of Ru(bpy)32+/TPA by malachite green and crystal violet

Efficient and stable quenching of electrochemiluminescence of Ru(bpy)3(2+)/TPA by malachite green(MG) and crystal violet(CV) at the glass carbon (GC) electrode is reported. A novel quenching mechanism has been proposed. Resonance energy transfer from the excited-state luminophore Ru(bpy)3(2+*) to MG/CV and dynamic quenching are suggested as the mechanism for quenching ECL. The quenching mechanism is discussed in detail based on UV-visible absorption spectra, cyclic voltammograms, ECL curves and fluorescence methods. MG shows more efficient quenching than CV. Moreover, the quenched ECL intensity versus the concentration of MG and CV are linear over the concentration ranges of 8 × 10(-10)-8 × 10(-7)M and 3.46 × 10(-9)-5.5 × 10(-7)M, respectively. The corresponding limit of detection (LOD) was 1.0 × 10(-10)M for MG and 1.1 × 10(-10)M for CV (S/N=3).

An electrochemical glutathione biosensor: Ubiquinone as a transducer

In this paper, coenzyme Q10 (Ubiquinone, CoQ10) was used for the first time as a transducer to construct electrochemical biosensor for effectively detecting γ-L-glutamyl-L-cysteinyl-glycine (glutathione, GSH). CoQ10 modified electrode was fabricated by attaching its gel mixed with multi-walled carbon nanotubes (MWNTs)/ionic liquid (IL). In the optimum conditions, based on the increasing of reduction peak current of CoQ10 caused by GSH through voltammetric technology, it was found that the peak current of CoQ10 was linear with the concentration of GSH in the range from 4.0×10(-9) to 2.0×10(-7)mol L(-1) at the pH 7.00, and the limit of detection was 3.2×10(-10)mol L(-1) (S/N=3). The results revealed that this method could be used to determine GSH in actual blood samples with the superiority of excellent selectivity, high stability and sensitivity. The strategy explored here might provide a new pathway to design novel multi-function transducers for detecting GSH, which has unique characteristic and potential application in the fields of sensor and medical diagnosis.

Detection of DNA damage induced by styrene oxide in dsDNA layer-by-layer films using adriamycin as electroactive probe

The detection of DNA damage is one of the most important topics in the DNA research fields. In this paper, an electrochemical method for the detection of DNA damage by combining the layer-by-layer assembly film with adriamycin (ADM) as an electrochemical probe was developed. Firstly, the layer-by-layer {dsDNA/PEI}(n) film was prepared by the alternate adsorption of polycationic polyethyleneimine (PEI) and negatively charged natural DNA onto glassy carbon electrode (GCE) surface. Its electrochemical behaviors were characterized by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV), and the optimal value of n was determined to be 2. Secondly, the {dsDNA/PEI}(2) film was immersed into the solution of ADM and the {dsDNA/PEI}(2)-ADM was obtained. While transferred into the blank solution, the {dsDNA/PEI}(2)-ADM would gradually release ADM, exhibiting the good reversibility of ADM incorporation. Finally, the DNA damage induced by styrene oxide (SO) was investigated and the promising results showed that the present method can be a useful tool for the detection of DNA damage.

Determination of m-dinitrobenzene based on novel type of sensor using thiol-porphyrin mixed monolayer-tethered polyaniline with intercalating fullerenols

A novel sensor based on thiol-porphyrin mixed monolayer-tethered polyaniline (PANI) with intercalating fullerenols was applied to sensitively detect m-dinitrobenzene (m-DNB) by differential pulse voltammetry (DPV). The thiolated polyaniline was examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrode modification of thiol-porphyrin mixed monolayer-tethered polyaniline with intercalating fullerenols exhibited a higher analytical sensitivity versus that of thiol-porphyrin mixed monolayer-tethered polyaniline, because the fullerenols in mixed monolayer could improve the preconcentration efficiencies of m-DNB. Under optimum conditions, the linear calibration curves ranged from 0.029 to 10,000 nmol L(-1) for m-DNB, with a limit of detection (S/N=3) of 9.72 pmol L(-1).