The optically pure 3-hydroxy-3′,4′-methylenedioxy flavone-6-carboxylic acid was obtained through the chalcone route. The structure of 3-hydroxy-3′,4′-methylenedioxy flavone-6-carboxylic acid was first elucidated by single crystal X-ray analysis: triclinic, space group, triclinic (P-1) with a = 8.1379(13) Å, b = 8.9831(14) Å, c = 13.198(2) Å, α = 88.413(2)°, β = 74.908(2)°, γ = 72.987(2)°. V = 889.5(2) Å3, Z = 2. The structure was solved by direct methods and refined to a final R = 0.0413 for 1630 reflections with I > 2σ(I). The crystal structure is stabilized by O–H···O and C–H···O hydrogen bondings and π–π stacking interactions.

In the title compound, C16H9BrO5·2C3H7NO, the chromene ring system is essentially planar. The two dimethylformamide solvent molecules are linked by intermolecular O—H⋯O hydrogen bonds to the 6-bromo-3-hydroxy-4-oxo-2-phenyl-4H-chromene-8-carboxylic acid molecules.

The title compound, C7H4Br2O3, has an intramolecular O-H center dot center dot center dot O = C hydrogen bond and aggregates to form hydrogen-bonded dimers via O-H center dot center dot center dot O interactions. The formation of zigzag one-dimensional molecular tapes via C-H center dot center dot center dot Br interactions and pi-pi stacking interactions (interplanar separation = 3.42 angstrom) completes the crystal structure.

A biosensor was investigated based on the use of ZrO2 sol–gel matrix for enzyme immobilization in the mild condition. This bioceramic zirconia alcogel has been prepared by the novel alcohothermal route with a cheap inorganic salt Zr(NO3)4·5H2O with several desirable features including a large surface area (about 460m2g−1) as well as pore volume and a well-developed textural mesoporosity, and horseradish peroxidase was selected as a model enzyme. The results of transmission electron microscopy (TEM) and BET measurement of the substrate showed that the as-prepared zirconia matrix has an advantageous microenvironment and large surface area available for high enzyme loading. The parameters affecting both the entrapment of enzyme and the biosensor response were optimized. The resulting biosensor exhibited high sensitivity of 111μAmM−1 for hydrogen peroxide over a wide range of concentrations from 2.5×10−7 to 1.5×10−4moll−1, quick response of less than 10s and good stability over 3 months.

Horseradish peroxidase was selected as a model enzyme to fabricate a novel biosensor based on the co-immobilization of thionine. The interaction between enzyme and sol-gel was further studied by ultraviolet-visible spectrum, which showed that sol-gel did not affect the bioactivity of the enzyme. The optimum conditions were pH 7.0, 25 degreesC, the applied potential was -0.22 V. The biosensor had a fast response with a linear calibration range of 1.76 x 10(-3) similar to 5.5 x 10(-2) mol/L, a detection limit of 1.1 x 10(-4) mol/L. Both sensitivity and selectivity of the biosensor were ideal. The biosensor remained 80% of its activity after using three weeks.

A novel BOD biosensor has been fabricated from a microbial membrane on an oxygen electrode; a porous inorganic Al2O3 sol–gel matrix was used to immobilize the yeast. Use of the sensor is convenient and rapid compared with the official BOD5 method. The gelation time required to form the microorganism membrane was less than 15 min. There was linear relationship between the response (sensor current) and BOD values ranging from 10–50 mg L–1. The lifetime of the BOD biosensor was more than 30 days at ambient temperature.

The multi-layered protein film, containing photosynthetic reaction center (RC) protein isolated from Rhodobacter sphaeriodes or its pigment-replaced mutants, was prepared with 4-Aminothiophenol (4-ATP) self-assembled monolayer (SAM) modified gold electrode. The RC protein was embedded in an ordered-orientated charged poly-styrenesulfonate (PSS) and poly(dimerthyldiallylammonium) chloride (PDDA) film successively. The reversible or quasi-reversible electron transfer (ET) for the re-constituted RC and its mutants was probed by cyclic voltammetry (CV) and square wave voltammetry (SWV), reflecting the electrochemical-driven electron recombination for RC protein or its mutants. The SWV data for RC and its mutants in the films were non-linearly fitted to get the electrochemical parameters.

A novel biosensor for the amperometric detection of hydrogen peroxide was developed based on the co-immobilization of catalase and methylene blue on an Al2O3 sol-gel fabricated glassy carbon electrode. The membrane structure;of the sol-gel-immobilized catalase and methylene blue was studied with scanning electron microscopy. Cyclic voltammetric and amperometric measurements demonstrated that methylene blue co-immobilized with catalase in this way displayed good stability and efficiently shuttled electron between the immobilized enzyme and the electrode. Electrocatalytic reduction of H2O2 at the electrode was evaluated with respect to solution pH, operating potential and selectivity.:The biosensor was stable at least for 3 weeks.

A new biosensor for the amperometric detection of hydrogen peroxide was developed based on the co-immobilization of horseradish peroxidase (HRP) and methylene blue on a β-type zeolite modified glassy carbon electrode without the commonly used bovine serum albumin-glutaraldehyde. The intermolecular interaction between enzyme and zeolite matrix was investigated using FT-IR. The cyclic voltammetry and amperometric measurement demonstrated that methylene blue co-immobilized with HRP in this way displayed good stability and could efficiently transfer electrons between immobilized HRP and the electrode. The sensor responded rapidly to H2O2 in the linear range from 2.5 × 10–6 to 4.0 × 10–3 M with a detection limit of 0.3 μM. The sensor was stable in continuous operation.