POLY(3,4-ETHYLENEDIOXYTHIOPHENE METHANOL)/ASCORBATE OXIDASE/NAFION-SINGLE-WALLED CARBON NANOTUBES BIOSENSOR FOR VOLTAMMETRIC DETECTION OF VITAMIN C

Vitamin C （VC） content in commercial juices was voltammetrically determined using a highly selective and sensitive poly（3,4-ethylenedioxythiophene methanol）/ascorbate oxidase/Nafion-single-walled carbon nanotubes （PEDOTM/AO/Nation-SWCNT） biosensor. The biocompatible PEDOTM matrix was prepared facilely by the one-step electrochemical deposition technique in lithium perehlorate aqueous solutions. AO was dip-coated on the surface of the biocompatible PEDOTM matrix. The mixture of Nafion-SWCNT was dip-cast onto the surface of AO layer when it was obtained by blending Nation solution and SWCNT dispersion together in a volume ratio of 1：1. The prepared PEDOTM/AO/Nafion-SWCNT biosensor was used for the voltammetric determination of VC, which exhibited the good linear range （4.0 ~ 10-s-3 x 10-s mol/L）, low detection limit （13 I^mol/L）, pronounced sensitivity （1.4072 mA （mmol/L） i cm 2）, high bioaftinity （low apparent Michaelis-Menten constant）, good stability （good repeatability）, high specificity （good anti-interference ability） coupled with the good reliability and feasibility （the determination of VC in commercial juices）. Meanwhile, the good aqueous solubility and the low onset oxidation potential of EDOTM will be more beneficial to the application in biosensor field compared to 3,4-ethylenedioxythiophene. Moreover, the good biocompatibility of PEDOTM matrix and high selectivity of Nation-SWCNT films also provide a promising platform for the development of biosensing devices.

Electrochemical determination of quercetin by self-assembled platinum nanoparticles/poly(hydroxymethylated-3,4-ethylenedioxylthiophene) nanocomposite modified glassy carbon electrode

A simple and sensitive platinum nanoparticles/poly（hydroxymethylated-3,4-ethylenedioxylthiophene） nanocomposite （PtNPs/PEDOT-MeOH） modified glassy carbon electrode （GCE） was successfully developed for the electrochemical determination of quercetin. Scanning electron microscopy and energy dispersive X-ray spectroscopy results indicated that the PtNPs were inserted into the PEDOT- MeOH layer. Compared with the bare GCE and poly（3,4-ethylenedioxythiophene） （PEDOT） electrodes, the PtNPs/PEDOT-MeOH/GCE modified electrode exhibited a higher electrocatalytic ability toward the oxidation of quercetin due to the synergic effects of the electrocatalytic activity and strong adsorption ability of PtNPs together with the good water solubility and high conductivity of PEDOT-MeOH. The electrochemical sensor can be applied to the quantification of quercetin with a linear range covering 0.04-91μmol L-1 and a low detection limit of 5.2 nmol L-1. Furthermore, the modified electrode also exhibited good reoroducibilitv and long-term stability, as well as high selectivity.

Electrochemical sensor based on f-SWCNT and carboxylic group functionalized PEDOT for the sensitive determination of bisphenol A

A simple, sensitive, and reliable method for the voltammetric determination of bisphenol A （BPA） by using carboxylic group functionalized single-walled carbon nanotubes （f-SWCNT）/carboxylic-functionalized poly（3,4-ethylenedioxythiophene） （PC4） complex modified glassy carbon electrode （GCE） has been successfully developed. The electrochemical behavior of BPA at the surface of the modified electrode is investigated by electrochemical techniques. The cyclic voltammetry results show that the as-prepared electrode exhibits strong catalytic activity toward the oxidation of BPA with a well-defined anodic peak at 0.623 V in PBS （0.1 mol/L, pH 7.0）. The surface morphology of the 3D network of composite film is beneficial for the adsorption ofanalytes. Under the optimized conditions, the oxidation peak current is proportional to BPA concentration in the range between 0.099 and 5.794 μmol/L （R2 = 0.9989）, with a limit of detection of 0.032 μmol/L （SIN = 3）. The enhanced performance of the sensor can be attributed to the excellent electrocatalytic property off-SWCNT and the extraordinary conductivity of PC4. Furthermore, the proposed modified electrode displays high stability and good reproducibility. The good result on the voltammetric determination of BPA also indicates that the asfabricated modified electrode will be a good candidate for the electrochemical determination and analysis of BPA.

POLY(THIOPHENE-3-ACETIC ACID)-PALLADIUM NANOPARTICLE COMPOSITE MODIFIED ELECTRODES FOR SUPERSENSITIVE DETERMINATION OF HYDRAZINE

A promising electrochemical sensor was fabricated by electrodeposition of Pd nanoparticles （PdNPs） on poly（thiophene-3-acetic acid） （PTAA）-modified glassy carbon electrode （GCE）, forming a PdNPs/PTAA composites-modified GCE （PdNPs/PTAA/GCE）. Scanning electron microscope （SEM） and electrochemical techniques were used for the characterization of these composites. It was found that the PdNPs/PTAA layer was very uniform. ]Electrochemical experiments showed that this proposed PdNPs/PTAA composites-modified electrode exhibited excellent electrocatalytic activity towards the oxidation of hydrazine. Under the optimum conditions, the proposed sensor can be applied to the quantification of hydrazine with a wide linear range from 8.0 × 10-9 mol/L to 1.0 × 10-5 mol/L with a low detection limit of 2.67 × 10-9 mol/L. The experiment results also showed that the sensor exhibited good reproducibility and long-term stability, as well as high selectivity with no interference from other potential competing species.

AN AMPEROMETRIC BIOSENSOR BASED ON COVALENT IMMOBILIZATION OF ASCORBATE OXIDASE ON BIOCOMPATIABLE AND LOW-TOXIC POLY(THIOPHENE-3-ACETIC ACID) MATRIX

The biocompatiable and low-toxic poly（thiophene-3-aeetic acid） （PTAA） matrix was successfully electrosynthesized in ionic liquid 1-butyl-3-metbylimidazolium hexafluorophosphate （BmimPF6） in comparison with the electrosynthesis of PTAA matrix in acetonitrile （ACN）. Ascorbate oxidase （AO） was used as a model for the development and application of biosensor. Vitamin C （VC） biosensors were facilely fabricated by the covalent immobilization of AO molecules on PTAA matrices electrosynthesized in ACN containing tetrabutylammonium tetrafluoroborate and BmimPF6, respectively. Electrochemical impedance spectroscopy, scanning electron microscopy and FTIR spectroscopy indicated that AO molecules were covalently immobilized on PTAA matrices. Parameters of the as-obtained biosensors such as working potential, pH and temperature have been optimized. The amperometric biosensor based on PTAA matrix electrosynthesized in BmimPF6 exhibited wider linear range, lower detection limit, higher sensitivity and bioaffinity, and better operational and storage stability than that electrosynthesized in ACN under optimal conditions. The as-obtained biosensor based on PTAA matrix electrosynthesized in BmimPF6 was employed for the detection of VC content in comme：rcial juices, and the result was close to the data given by manufacturers. Excellent results indicate that the PTAA matrix electrosynthesized in ionic liquid is a promising platform for the covalent immobilization of biologically-active species and the development of biosensors.

One-step co-electrodeposition of graphene oxide doped poly(hydroxymethylated-3,4-ethylenedioxythiophene) film and its electrochemical studies of indole-3-acetic acid

A novel graphene oxide （GO） doped poly（hydroxymethylated-3,4-ethylenedioxythiophene） （PEDOTM） film has been achieved via one-step co-electrodeposition and utilized for electrochemical studies of indole-3-acetic acid （IAA）. The incorporation of GO into PEDOTM film facilitated the electrocatalytic activity and exhibited a favorable interaction between the PEDOTM/GO film and the phytohormone during the oxidation of IAA. Under optimized conditions, differential pulse voltammetry and square wave voltammetry were used for the quantitative analysis of IAA, respectively, each exhibiting a wide linearity range from 0.6 μmol L-1 to 10 μmol L-1 and 0.05 μmol L-1 to 40 μmol L-1, good sensitivity with a low detection Iimit of 0.087 μmol L-1 and 0.033μmol L T, respectively, as well as good stability. With the notable advantages of a green, sensitive method, expeditious response and facile operation, the as-prepared PEDOTM/GO organic-inorganic composite film provides a promising platform for electrochemical studies of IAA.