•Hydrogen-magnetic immobilized GOD complex was prepared.•A fiber optic sensor based on PMIGC and COD was developed.•The sensor can detect cholesterol and glucose sequentially.•The sensor has good properties and can be used for real samples.This work described a temperature-triggered fiber optic biosensor for sequential detection of cholesterol and glucose based on poly(N-isopropylacrylamide)-co-acrylamide)(P(NIPAAm-co-AAm))-magnetic immobilized glucose oxidase(GOD) complex (PMIGC) and magnetic immobilized cholesterol oxidase (COD). At 38 °C, the sensor will selectively detect cholesterol concentration with the detection range of 25–250 mg/dL since P(NIPAAm-co-AAm) is known to shrink above its lower critical solution temperature (LCST) of 36 °C, and will separate GOD from analytes so that PMIGC has no catalysis effect on glucose. When the temperature was switched to 25 °C (below LCST), PMIGC could catalyze the oxidation of glucose since GOD will be exposed to analytes due to the swell of P(NIPAAm-co-AAm). This sensor can be used for the detection of glucose with the detection range of 50–700 mg/dL. The optimal detection conditions for cholesterol were achieved with pH 7.0, 40 °C and 10 mg COD (in 75 mg carrier), and those for glucose were achieved with pH6.5, 35 °C and 12 mg GOD (in 90 mg carrier). The biosensor proposed is shown to have outstanding repeatability, selectivity and yield satisfactory detection results on practical samples.Download high-res image (110KB)Download full-size imageA fiber optic biosensor was developed to perform the sequential detection of cholesterol and glucose at different temperature (38 °C and 25 °C)

•PNIPAAm was combined with immobilized GOD to form PIGC.•PIGC could have switching effect for catalysis to glucose oxidation.•A temperature controllable glucose sensor based on PIGC was developed.•This sensor has good properties and can detect glucose in real samples.A novel fiber optic glucose biosensor based on Poly(N-isopropylacrylamide) (PNIPAAm)-immobilized glucose oxidase (GOD) complex (PIGC) was developed. PIGC was prepared by combining PNIPAAm with GOD immobilized on SiO2 nanoparticles using in-situ complex method. The catalyzation of oxidation of glucose could be controlled based on the feature that PNIPAAm exhibited swelling and shrinking response to the temperature below and above low critical solution temperature (LCST), respectively. The biosensor can perform the controllable detection of glucose by changing temperature. The optimal detection conditions for this biosensor were achieved at pH 6.5, 30 °C and 10 mg of GOD amount. There is a good linear relationship between the phase delay difference φ and the glucose concentration in the range of 50–700 mg/dL. This biosensor has good repeatability, selectivity and can be used for the detection of practical samples.

•COD was immobilized on magnetic fluorescent core-shell structured nanoparticles.•The nanoparticles were optical sensitive to oxygen in water solution.•The nanoparticles have remarkable improved stability compared with free COD.•The nanoparticles can probably be used in multi parameter fiber optic Biosensor.The magnetic fluorescent core-shell structured nanoparticles, Fe3O4@SiO2(F)@meso–SiO2 nanoparticles, were prepared. Cholesterol oxidase (COD) was immobilized on their surface to form Fe3O4@SiO2(F)@meso–SiO2@COD nanoparticles. Optimal immobilization was achieved with 2.5% (v/v) APTES, 2.0% (v/v) GA, 10 mg COD (in 15 mg carrier) and solution pH of 7.0. Fe3O4@SiO2(F)@meso–SiO2@COD nanoparticles showed maximal catalytic activity at pH 7.0 and 50 °C. The thermal, storage and operational stabilities of COD were improved greatly after its immobilization. After the incubation at 50 °C for 5 h, the nanoparticles and free COD retained 80% and 46% of its initial activity, respectively. After kept at 4 °C for 30 days, the nanoparticles and free COD maintained 86% and 65% of initial activity, respectively. The nanoparticles retained 71% of its initial activity after 7 consecutive operations. Since Fe3O4@SiO2(F)@meso–SiO2@COD nanoparticles contained tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate (Ru(bpy)3Cl2) and were optical sensitive to oxygen in solution, it might be used as the sensing material and has the application potential in multi parameter fiber optic biosensor based on enzyme catalysis and oxygen consumption.

•MnPc could catalyze chromogenic oxidation of chlorophenols under sunlight.•Dioxygen is oxidant and activated in photocatalytic oxidation process.•Singlet oxygen and superoxide anion radical are main active oxygen species.•A detailed photocatalytic mechanism was proposed for chromogenic reaction.A manganese phthalocyanine (MnPc) photocatalytic system for chromogenic identification of several chlorophenol pollutants was reported for the first time. In this system, 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol pollutants could be oxidized by dissolved oxygen in the presence of MnPc under sunlight irradiation, and quickly transformed into pink dyes assisted with 4-aminoantipyrine (4-AAP). Control experiments testified that singlet oxygen (1O2) and superoxide anion radicals (O2-) were the two key active species for the rapid formation of pink dyes, which were considered to be generated via the combination of well-known metal phthalocyanine mediated Type I and Type II mechanism.

The novel water-soluble and sterically hindered phthalocyanine complexes, i.e. iron(III) tetra-(4-carboxyphenoxy)phthalocyanine (3) and iron(III) tetra-(8-quinolineoxy-5-sulfonicacid)phthalocyanine (4) were synthesized for fast detection of phenolic pollutants. These two FePc complexes exhibited the high catalytic activity in the chromogenic reactions of phenolic pollutants. Five phenolic substrates, including phenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol and 1-naphthol could be efficiently oxidized by tert-butyl hydroperoxide in the presence of these selected FePc catalyst. UV–Vis spectroscopy and HPLC technique were used to monitor the catalyzed oxidation of phenolic substrates. Compared with catalytic methods by other reported phthalocyanines, this system has the obvious advantages of fast oxidation and high-yield conversion of phenolic substrates. Under the optimal conditions, the chromogenic process of 2-chlorophenol could be completed just within 10 min with more than 90 % of conversion. Potentially, this system is promising for the application of fast chromogenic identification of phenolic pollutants.

A novel system for catalytic oxidation of phenol and chlorophenol pollutant in water by tetranitro iron (II) phthalocyanine (TNFe(II)Pc) is reported for the first time. In this system, several phenolic substrates (phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol) could be easily oxidized by naturally dissolved oxygen in the presence of TNFe(II)Pc, and then rapidly combined with 4-aminoantipyrine to generate the pink dye. The catalytic oxidation process and resulting products were monitored by UV–Vis spectroscopy and high performance liquid chromatography–mass spectrometer (HPLC–MS) technique. Control experiments demonstrated that the generation of superoxide anion radical was crucial for the dye formation, and a possible mechanism involved a successive single electron transfer from phenolic substrates to O2 via the axis of TNFe(II)Pc was proposed. Potentially, this system is promising for application in chromogenic identification of phenolic pollutant.Graphical abstractHighlights► TNFe(II)PC could catalyze oxidation of phenol and chlorophenol pollutant. ► Dioxygen is oxidant and sufficient for the catalytic oxidation reaction. ► Superoxide anion radical is the active species generated in catalytic process. ► Successive single electron transfer is the key step of catalytic mechanism.

Using SiO2 nanoparticles as a carrier, a novel immobilized glucose oxidase (GOD) (EC1.1.3.4) was prepared via crosslinking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, 2% (v/v) 3-aminopropiltrietoxysilane (APTS), 2.5 mg GOD (in 34 mg carrier) and solution pH of 6.5. The immobilized GOD showed maximal catalytic activity at pH 7.0 and 60 °C, and more than 85% of initial activity at the temperature from 20 °C to 80 °C. After immobilization, the enzyme exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 85% of its initial activity after the incubation at 45 °C for 360 min, whereas free enzyme had only 23% of initial activity after the same incubation. After kept at 4 °C for 30 days, the immobilized and free enzyme retained 84% and 60% of initial activity, respectively. The immobilized GOD also preserved 87% of its initial activity after six consecutive operations.Research highlights► GOD was immobilized covalently on SiO2 nanoparticles. ► Immobilized GOD shows outstanding activity in broad pH and temperature range. ► Immobilized GOD has remarkable improved thermal, storage and operation stability compared with free GOD. ► This immobilized GOD is a promising candidate for the development of fiber optic GOD sensor.

Glucose oxidase (GOD) was covalently immobilized onto Fe3O4/SiO2 magnetic nanoparticles (FSMNs) using glutaraldehyde (GA). Optimal immobilization was at pH 6 with 3-aminopropyltriethoxysilane at 2% (v/v), GA at 3% (v/v) and 0.143 g GOD per g carrier. The activity of immobilized GOD was 4,570 U/g at pH 7 and 50°C. The immobilized GOD retained 80% of its initial activity after 6 h at 45°C while free enzyme retained only 20% activity. The immobilized GOD maintained 60% of its initial activity after 6 cycles of repeated use and retained 75% of its initial activity after 1 month at 4°C whereas free enzymes retained 62% of its activity.

The magnetic chitosan nanoparticles were prepared by reversed-phase suspension method using Span-80 as an emulsifier, glutaraldehyde as cross-linking reagent. And the nanoparticles were characterized by TEM, FT-IR and hysteresis loop. The results show that the nanoparticles are spherical and almost superparamagnetic. The laccase was immobilized on nanoparticles by adsorption and subsequently by cross-linking with glutaraldehyde. The immobilization conditions and characterizations of the immobilized laccase were investigated. The optimal immobilization conditions were as follows: 10 mL of phosphate buffer (0.1 M, pH 7.0) containing 50 mg of magnetic chitosan nanoparticles, 1.0 mg · mL−1 of laccase and 1% (v/v) glutaraldehyde, immobilization temperature of 4°C and immobilization time of 4 h. The immobilized laccase exhibited an appreciable catalytic capability (480 units · g−1 support) and had good storage stability and operation stability. The Km of immobilized and free laccase for ABTS were 140.6 and 31.1 μM in phosphate buffer (0.1 M, pH 3.0) at 37 °C, respectively. The immobilized laccase is a good candidate for the research and development of biosensors based on laccase catalysis.

Two novel mixed-ligand complexes, [M(phen)2(ans)2]·H2O (M = Cd(II) 1, Zn(II) 2; phen is 1, 10-phenanthroline, and ans is 4-aminonaphthalene-1-sulfonate), were obtained from the reaction of 1, 10-phenanthroline, sodium 4-aminonaphthalene-1-sulfonate tetrahydrate and acetate in mixed solvents. Interaction of the complexes with calf thymus DNA (ctDNA) were investigated using UV-vis absorption spectra, luminescence titrations, steady-state emission quenching by [Fe(CN)6]4−, DNA competitive binding with ethidium bromide (EB) and viscosity measurements. The experimental results indicate that there exist two interaction modes between the complexes and DNA, namely the electrostatic interaction and intercalation, with the binding constants of 1.82 × 105 M−1 for 1 and 4.78 × 104 M−1 for 2 in buffer of 50 mM NaCl and 5 mM Tris-HCl (pH 7.0).

The oxidation of adrenaline by dioxygen using copper phthalocyanine (CuPc) as the catalyzer was studied. CuPc has the optimal catalytic pH of 8.0 and the optimal catalytic temperature of 55 °C. It also has good storage and operation stability. The fiber optic adrenaline biosensor based on CuPc catalysis and fluorescence quenching was fabricated and studied. This sensor has the detection range of 7.0×10−5–1.5×10−4 mol/L, the response time of 4 min, good reproducibility and stability.