Haohua He

A cost-effective and practical polybenzanthrone-based fluorescent sensor for efficient determination of palladium (II) ion and its application in agricultural crops and environment.

A highly selective and sensitive fluorescent chemosensor suitable for practical measurement of palladium ion (Pd(2+)) in agricultural crops and environment samples has been successfully fabricated using polybenzanthrone (PBA). PBA was facilely electrosynthesized in the mixed electrolyte of acetonitrile and boron trifluoride diethyl etherate. The fluorescence intensity of PBA showed a linear response to Pd(2+) in the concentration range of 5 nM-0.12 mM with a detection limit of 0.277 nM and quantification limit of 0.925 nM. Different compounds existing in agricultural crops and environment such as common metal ions, anions, natural amino acids, carbohydrates, and organic acids were used to examine the selectivity of the as-fabricated sensor, and no obvious fluorescence change could be observed in these interferents and their mixtures. A possible mechanism was proposed that the coordination of PBA and Pd(2+) enhance the aggregation of polymer chains, which led to a significant quenching of PBA emission, and this was further confirmed by absorption spectra monitoring and transmission electron microscopy. The excellent performance of the proposed sensor and satisfactory results of the Pd(2+) determination in practical samples suggested that the PBA-based fluorescent sensor for the determination of Pd(2+) will be a good candidate for application in agriculture and environment.

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/Nafion-SWCNT) biosensor. The biocompatible PEDOTM matrix was prepared facilely by the one-step electrochemical deposition technique in lithium perchlorate 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 Nafion 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 × 10−5−3 × 10−3 mol/L), low detection limit (13 μmol/L), pronounced sensitivity (1.4072 mA (mmol/L)−1 cm−2), high bioaffinity (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 Nafion-SWCNT films also provide a promising platform for the development of biosensing devices.

Electrosynthesis of Poly(thiophene-3-acetic Acid) Film in Ionic Liquids for Covalent Immobilization of Biologically Active Species

Poly(thiophene-3-acetic acid) (PTAA) film with good biocompatibility, low toxicity, and high conductivity was electrosynthesized in an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. Glutamate oxidase (GO), one of biologically active species, was covalently immobilized on the surface of PTAA film for the design and fabrication of the electrochemical biosensor. The impedance spectroscopy, infrared spectra, and scanning electron microscopy indicated that GO molecules were successfully immobilized on the surface of PTAA film. The oxidation current increased linearly with the concentration of L-glutamic acid in the range from 6 × 10−7 to 3 × 10−3 M with a regression coefficient of 0.998. The limit of detection was found to be 0. 23 µM, this method also provided a sensitivity of 87.1 mA M−1 cm−2, and a response time of less than 5 s. Moreover, the bioaffinity and operational and storage stability of the biosensor were also evaluated. Satisfactory results indicated that the resulting PTAA film is a promising candidate for the covalent immobilization of biologically active 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-acetic acid) (PTAA) matrix was successfully electrosynthesized in ionic liquid 1-butyl-3-methylimidazolium 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 commercial 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.

Amperometric vitamin C biosensor based on the immobilization of ascorbate oxidase into the biocompatible sandwich-type composite film.

Ascorbate oxidase (AO), a biologically active macromolecule, was successfully immobilized into a biocompatible sandwich-type composite film for developing the vitamin C (VC) biosensor, and the content of VC in commercial juices was amperometrically determined. The biocompatible and conducting poly(3,4-ethylenedioxythiophene) composite film and highly stable and selective multiwalled carbon nanotubes –Nafion composite film were prepared as inner and outer films of biosensor. AO molecules were immobilized between these two composite films. The as-fabricated biosensor displayed an excellent bioelectrocatalytic performance towards the oxidation of VC, a fast current response, a low working potential, a high sensitivity, a wide linear range, and a low detection limit. Moreover, the working mechanism of the biosensor was proposed, and its kinetics was also discussed. In addition, the specificity, reproducibility, and feasibility of the as-fabricated biosensor were also evaluated. Good results of the VC determination in commercial juices indicated that the as-fabricated biosensor was a potential candidate for the electrochemical determination of VC in agricultural crops. Inner and outer films provided a promising platform for the immobilization of biologically active species.