Litong Jin

A Photoelectrochemical Immunosensor Based on Au‐Doped TiO2 Nanotube Arrays for the Detection of α‐Synuclein

α-Synuclein (α-SYN) is a very important neuronal protein that is associated with Parkinsons disease. In this paper, we utilized Au-doped TiO(2) nanotube arrays to design a photoelectrochemical immunosensor for the detection of α-SYN. The highly ordered TiO(2) nanotubes were fabricated by using an electrochemical anodization technique on pure Ti foil. After that, a photoelectrochemical deposition method was exploited to modify the resulting nanotubes with Au nanoparticles, which have been demonstrated to facilitate the improvement of photocurrent responses. Moreover, the Au-doped TiO(2) nanotubes formed effective antibody immobilization arrays and immobilized primary antibodies (Ab(1)) with high stability and bioactivity to bind target α-SYN. The enhanced sensitivity was obtained by using {Ab(2)-Au-GOx} bioconjugates, which featured secondary antibody (Ab(2)) and glucose oxidase (GOx) labels linked to Au nanoparticles for signal amplification. The GOx enzyme immobilized on the prepared immunosensor could catalyze glucose in the detection solution to produce H(2)O(2), which acted as a sacrificial electron donor to scavenge the photogenerated holes in the valence band of TiO(2) nanotubes upon irradiation of the other side of the Ti foil and led to a prompt photocurrent. The photocurrents were proportional to the α-SYN concentrations, and the linear range of the developed immunosensor was from 50 pg  mL(-1) to 100 ng  mL(-1) with a detection limit of 34 pg  mL(-1). The proposed method showed high sensitivity, stability, reproducibility, and could become a promising technique for protein detection.

Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO(2) film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO(2) film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO(2) and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO(2) film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO(2) film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO(2) film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1mgl(-1), COD values with the linear range of 0.3-10.0mgl(-1) were achieved. The results were in good agreement with those from the conventional COD methods.

Application of nano TiO2 towards polluted water treatment combined with electro-photochemical method

A novel composite reactor was prepared and studied towards the degradation of organic pollutants in this work. In the reactor, a UV lamp was installed to provide energy to excite nano TiO(2), which served as photocatalyst, leading to the production of hole-electron pairs, and a three-electrode electrolysis system was used to accumulate H(2)O(2) which played an important role in the degradation process. The reactor was evaluated by the degradation process of rhodamine 6G (R-6G), and the data obtained in the experiments showed that the combination of the photochemical and electrochemical system raised the degradation rate of R-6G greatly; the working mechanism of the reactor was also discussed in the article. The prepared reactor was also utilized to treat polluted water from dyeing and printing process. After continuous treatment for 0.5h, chemical oxygen demand biochemical oxygen demand, quantity of bacteria and ammonia nitrogen of the polluted water were reduced by 93.9%, 87.6%, 99.9% and 67.5%, respectively, which indicated that the method used here could be used for effective organic dyes degradation.

A Nafion-coated bismuth film electrode for the determination of heavy metals in vegetable using differential pulse anodic stripping voltammetry: An alternative to mercury-based electrodes

Mercury electrodes have been traditionally employed for achieving high reproducibility and sensitivity of the stripping technique. However, new alternative electrode materials are highly desired because of the toxicity of mercury. Bismuth is an electrode material characterized by its low toxicity and its ability to form alloys with some metals such as cadmium, lead and zinc, allowing their preconcentration at the electrode surface. In this work, we reported the simultaneous determination of Pb(II), Cd(II) and Zn(II) at the low μg/l concentration levels by differential pulse anodic stripping voltammetry (DPASV) on a Nafion-coated bismuth film electrode (NCBFE) plated in situ, and investigated the application of NCBFE to heavy metals analysis in vegetable samples. The analytical performance of NCBFE was evaluated for simultaneous determination of Pb(II), Cd(II) and Zn(II) in non-deaerated solution, with the limits of determination of 0.30μg/l for Zn, 0.17μg/l for Cd and Pb at a preconcentration time of 180s. High reproducibility for NCBFE was indicated from the relative standard deviations of 2.4% for Pb, 2.0% for Cd and 3.4% for Zn at the 15μg/l level (n=15). The NCBFE was successfully applied to determine Pb and Cd in vegetable samples, and the results were in agreement with those of graphite furnace atomic absorption spectrometry (GFAAS).

Layer-by-Layer self-assembled acetylcholinesterase/PAMAM-Au on CNTs modified electrode for sensing pesticides

In this paper, an acetylcholinesterase (AChE)/dendrimers polyamidoamine (PAMAM)-Au/Carbon nanotubes (CNTs) multilayer modified electrode based on LbL self-assembled technique was employed in the detection of carbofuran in samples. The configuration of the nanostructure on the electrode provided a favorable environment to the immobilization of AChE. The modified films also improved the electrocatalytic characteristics and electron transfer speed between the films and the surface of electrode. The PAMAM-Au nanoparticles were characterized by SEM and UV-VIS methods. A set of experimental conditions were also optimized for the detection of the pesticides. A linear response over carbofuran concentration in the range of 4.8x10(-9)M to 0.9x10(-7)M was exhibited with a detection limit of 4.0x10(-9)M. The biosensor showed high sensitivity, good stability and reproducibility with promising application.

ZnO nanorods/Au hybrid nanocomposites for glucose biosensor

ZnO nanorods/Au hybrid nanocomposites (ZnO/Au) with Au nanocrystals growing on the surface of ZnO nanorods were synthesized via a simple and facile hydrothermal route. The prepared ZnO/Au nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) for the morphology study. The composites had a good electron transferring and biocompatibility. The glucose biosensor was fabricated by entrapping glucose oxidase (GOx) in this composite matrix using cross-linking method with glutaraldehyde and Nafion solutions. The proposed biosensor responded to glucose linearly over concentration range of 0.1-33.0 μM (R(2)=0.9956), and the detection limit was 10nM (S/N=3) at an operating potential of +0.55 V in pH 7.4 phosphate buffered solution (PBS). The biosensor exhibited a high and reproducible sensitivity, short response time (within 5s), good storage stability and high affinity to GOx (K(M)(app)=0.41 mM). The effects of electroactive interferents at the testing conditions can be negligible which showed a good selectivity of the biosensor. It is estimated that this ZnO/Au is an attractive material for the fabrication of efficient amperometric biosensors.

Combining biofunctional magnetic nanoparticles and ATP bioluminescence for rapid detection of Escherichia coli.

A rapid, specific and sensitive method for assay of Escherichia coli (E. coli) using biofunctional magnetic nanoparticles (BMNPs) in combination with adenosine triphosphate (ATP) bioluminescence was proposed. The BMNPs were fabricated by immobilizing a specific anti-E. coli antibody on the surface of amine-functionalized magnetic nanoparticles (about 20nm in diameter), and then was applied to capture the target bacteria E. coli from samples. The BMNPs exhibited high capture efficiency to E. coli. Transmission electron microscope (TEM) images showed that the BMNPs were bound to the surface of entire E. coli cells. The target bacteria became magnetic so that could be isolated easily from the sample solution by employing an external magnetic field. The concentration of E. coli captured by the BMNPs was then detected by an ATP bioluminescence method. The optimization of ATP measurement was carried out to improve the detection sensitivity. The proposed method was applied to detect the E. coli inoculated into pasteurized milk with low detection limit (20 cfu/mL) and short detection time (about 1h).

Sensitive determination of dopamine on poly(aminobenzoic acid) modified electrode and the application toward an experimental Parkinsonian animal model

Recent research on the pathology and treatment of Parkinsons disease (PD) necessitates the development of methods for analysis of dopamine (DA), an electroactive substance whose content reduces in patients with PD. The concentration variation of dopamine in an experimental Parkinsonian animal model and a treatment model was studied in this paper. For the purpose of detecting dopamine sensitively, a poly(para-aminobenzoic acid) (P-pABA) electrochemically modified glassy carbon electrode was prepared. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry. Under optimum conditions, the P-pABA modified electrode showed high sensitivity to DA oxidation. Coupled with high-performance liquid chromatography, the modified electrode was utilized to detect dopamine in rat brain dialysate with the linear range over three orders of magnitude and the detection limit of 2.0x10(-8) mol l(-1) (S/N=3). By treatment with reserpinum, an experimental Parkinsonian animal model was produced. Levodopa (L-dopa) and sodium nitroprusside (SNP) were used as drugs for treatment PD in this work. The dopamine level in PD model was only 22.4% that of the control one. PD rats could recover after therapy of L-dopa or SNP and the dopamine level increased sixfold compared with those not treated with drugs.

Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography

A multiwall carbon nanotubes (MWNTs) film modified electrode was prepared and used as an amperometric sensor for the simultaneous determination of oxidizable amino acids including cysteine, tryptophane and tyrosine. The electrochemical behaviors of these amino acids at this modified electrode were studied by cyclic voltammetry (CV). The results indicated that the MWNTs chemically modified electrode (CME) exhibited efficient electrocatalytic activity towards the oxidation of these amino acids with relatively high sensitivity, stability and long-life. Following separation by ion chromatography (IC) with 2.0 x 10(-3) mol l(-1) citric acid buffer solution (pH 6.5) as eluent, cysteine, tryptophane and tyrosine could be determined by the MWNTs CME successfully. Under the optimal conditions, the detection limits were 7.0 x 10(-7) mol l(-1) for cysteine, 2.0 x 10(-7) mol l(-1) for tryptophane and 3.5 x 10(-7) mol l(-1) for tyrosine at the signal-to-noise of 3, respectively. The method was applied successfully to the determination of these substances in plasma.

Study of carbon nanotubes-HRP modified electrode and its application for novel on-line biosensors.

In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs-HRP modified electrode as a working electrode. The MWCNTs-HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV (vs. Ag/AgCl). We assembled the MWCNTs-HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 x 10(-7) to approximately 2.0 x 10(-4) mol L(-1). The detection limit is 1.0 x 10(-7) mol L(-1) (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at -300 mV. Stability and reproducibility of the MWCNTs-HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs-HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2.