Magnetic self-assembled label-free electrochemical biosensor based on Fe3O4/α-Fe2O3 heterogeneous nanosheets for the detection of Tau proteins.

A type of electrochemical biosensors based on magnetic Fe3O4/α-Fe2O3 heterogeneous nanosheets was constructed to detect Tau proteins for early diagnosis and intervention therapy of Alzheimer's disease (AD). Firstly, Fe3O4/α-Fe2O3 heterogeneous nanosheets were fabricated as the substrate to realize magnetic self-assembly and magnetic separation to improve current response, and Fe3O4/α-Fe2O3@Au-Apt/ssDNA/MCH biosensors were successfully constructed through the reduction process of chloroauric acid, the immobilizations of aptamer (Apt) and ssDNA, and the intercept process of 6-Mercapto-1-hexanol (MCH); the construction process of the electrochemical biosensor was monitored using Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the factors affecting the current response of this sensor (concentration of Fe3O4/α-Fe2O3@Au and Apt/ssDNA, incubation temperature and time of Tau) were explored and optimized using differential pulse voltammetry (DPV). Analyzing the performance of this sensor under optimal conditions, the linear range was finally obtained to be 0.1 pg/mL-10 ng/mL, the limit of detection (LOD) was 0.08 pg/mL, and the limit of quantification (LOQ) was 0.28 pg/mL. The selectivity, reproducibility and stability of the biosensors were further investigated, and in a really sample analysis using human serum, the recoveries were obtained in the range of 93.93 %-107.39 %, with RSD ranging from 1.05 % to 1.94 %.

Nucleic acid aptasensor with magnetically induced self-assembly for the detection of EpCAM glycoprotein.

A "turn-on" aptasensor for label-free and cell-free EpCAM detection was constructed by employing magnetic α-Fe2O3/Fe3O4@Au nanocomposites as a matrix for signal amplification and double-stranded complex (SH-DNA/Apt probes) immobilization through Au-S binding. α-Fe2O3/Fe3O4@Au could be efficiently assembled into uniform and stable self-assembly films via magnetic-induced self-assembly technique on a magnetic glassy carbon electrode (MGCE). The effectiveness of the platform for EpCAM detection was confirmed through differential pulse voltammetry (DPV). Under optimized conditions, the platform exhibited excellent specificity for EpCAM, and a strong linear correlation was observed between the current and the logarithm of EpCAM protein concentration in the range 1 pg/mL-1000 pg/mL (R2 = 0.9964), with a limit of detection (LOD) of 0.27 pg/mL. Furthermore, the developed platform demonstrated good stability during a 14-day storage test, with fluctuations remaining below 93.33% of the initial current value. Promising results were obtained when detecting EpCAM in spiked serum samples, suggesting its potential as a point-of-care (POC) testing.

Electrochemical peptide nucleic acid functionalized α-Fe2O3/Fe3O4 nanosheets for detection of CYP2C19*2 gene.

The CYP2C19*2 gene carriers and non-carriers are closely related to the dosage of clopidogrel. To correctly guide the use of clopidogrel and promote individualized therapy, an ultra-sensitive electrochemical biosensor was developed for the detection of CYP2C19*2 gene. The heterogeneous α-Fe2O3/Fe3O4 nanosheets were prepared via the hydrothermal-calcination process, and the preparation parameters were optimized. The average diameter and thickness of the nanosheets were approximately 150 nm and 53 nm, respectively; and the saturation magnetization was 80.2 emu/g. The α-Fe2O3/Fe3O4@Au nanosheets were prepared by sodium borohydride reduction method, and self-assembled to the electrode surface with magnetic field. Ultra-sensitive detection of CYP2C19*2 gene was realized through the recognition ability of strong single base mismatching of peptide nucleic acid and signal amplification effect of magnetic α-Fe2O3/Fe3O4@Au nanosheets. Under optimal detection conditions, the current had a good linear correlation with the negative logarithm of CYP2C19*2 gene concentration in the range 1 pM-1 nM, and the detection limit was 0.64 pM (S/N = 3). Meanwhile, the electrochemical signals of target DNA and incomplete complementary DNA were detected. The constructed biosensor exhibited good selectivity, reproducibility, and stability, providing a promising strategy for the detection of other gene mutations by electrochemical biosensors.

Electrochemical sensor based on Fe3O4/α-Fe2O3@Au magnetic nanocomposites for sensitive determination of the TP53 gene.

Considering the high cost and tedious process of gene sequencing, there is an urgent need to develop portable and efficient sensors for the TP53 gene. Here, we developed a novel electrochemical sensor that detected the TP53 gene using magnetic peptide nucleic acid (PNA)-modified Fe3O4/α-Fe2O3@Au nanocomposites. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed the successful stepwise construction of the sensor, especially the high-affinity binding of PNA to DNA strands, which induced different electron transfer rates and resulted in current changes. Variations in the differential pulse voltammetry current observed during hybridization at different surface PNA probe densities, hybridization times, and hybridization temperatures were explored. The biosensing strategy obtained a limit of detection of 0.26 pM, a limit of quantification of 0.85 pM, and a wide linear range (1 pM-1 µM), confirming that the Fe3O4/α-Fe2O3@Au nanocomposites and the strategy based on magnetic separation and magnetically induced self-assembly improved the binding efficiency of nucleic acid molecules. The biosensor was a label-free and enzyme-free device with excellent reproducibility and stability that could identify single-base mismatched DNA without additional DNA amplification procedures, and the serum spiked experiments revealed the feasibility of the detection approach.

Immobilization and property of penicillin G acylase on amino functionalized magnetic Ni0.3Mg0.4Zn0.3Fe2O4 nanoparticles prepared via the rapid combustion process.

Penicillin G acylase plays an important role in the biocatalytic process of semi-synthetic penicillin. In order to overcome the disadvantages of free enzymes and improve the catalytic performance of enzymes, it is a new method to immobilize enzymes on carrier materials. And magnetic materials have the characteristics of easy separation. In the present study, the Magnetic Ni0.3Mg0.4Zn0.3Fe2O4 nanoparticles were successfully prepared by a rapid-combustion method and calcined at 400°C for 2 h. The surface of the nanoparticles was modified with sodium silicate hydrate, and the PGA was covalently bound to the carrier particles through the cross-linking of glutaraldehyde. The results showed that the activity of immobilized PGA reached 7121.00 U/g. The optimum pH for immobilized PGA was 8 and the optimum temperature was 45°C, the immobilized PGA exhibited higher stability against changes in pH and temperature. The Michaelis-Menten constant (Km) values of the free and immobilized PGA were 0.00387 and 0.0101 mol/L and the maximum rate (Vmax) values were 0.387 and 0.129 µmol/min. Besides, the immobilized PGA revealed excellent cycling performance. The immobilization strategy presented PGA had the advantages of reuse, good stability, cost saving and had considerable practical significance for the commercial application of PGA.

Effect and mechanism of paclitaxel loaded on magnetic Fe3O4@mSiO2-NH2-FA nanocomposites to MCF-7 cells.

Magnetic Fe3O4 nanoparticles were prepared via a simple hydrothermal method and utilized to load paclitaxel. The average particle size of Fe3O4 nanoparticles was found to be 20.2 ± 3.0 nm, and the calculated saturation magnetization reached 129.38 emu/g, verifying superparamagnetism of nanomaterials. The specific surface area and pore volume were 84.756 m2/g and 0.265 cm3/g, respectively. Subsequently, Fe3O4@mSiO2 nanoparticles were successfully fabricated using the Fe3O4 nanoparticles as precursors with an average size of 27.81 nm. The relevant saturation magnetization, zeta potential, and specific surface area of Fe3O4@mSiO2-NH2-FA were respectively 76.3 emu/g, -14.1 mV, and 324.410 m2/g. The pore volume and average adsorption pore size were 0.369 cm3/g and 4.548 nm, respectively. Compared to free paclitaxel, the solubility and stability of nanoparticles loaded with paclitaxel were improved. The drug loading efficiency and drug load of the nanoformulation were 44.26 and 11.38%, respectively. The Fe3O4@mSiO2-NH2-FA nanocomposites were easy to construct with excellent active targeting performance, pH sensitivity, and sustained-release effect. The nanoformulation also showed good biocompatibility, where the cell viability remained at 73.8% when the concentration reached 1200 µg/mL. The nanoformulation induced cell death through apoptosis, as confirmed by AO/EB staining and flow cytometry. Western blotting results suggested that the nanoformulation could induce iron death by inhibiting Glutathione Peroxidase 4 (GPX4) activity or decreasing Ferritin Heavy Chain 1 (FTH1) expression. Subsequently, the expression of HIF-1α was upregulated owing to the accumulation of reactive oxygen species (ROS), thus affecting the expression of apoptosis-related proteins regulated by p53, inducing cell apoptosis.

Acute effects of two different work-to-rest ratio of high-intensity interval training on brain-derived neurotrophic factor in untrained young men.

Background: Aerobic exercise could produce a positive effect on the brain by releasing brain-derived neurotrophic factor (BDNF). In untrained healthy humans there seems to be a linear correlation between exercise duration and the positive effect of acute aerobic exercise on brain-derived neurotrophic factor levels. Therefore, we performed two different duration of high-intensity interval training protocols (HIIT), both known to improve cardiovascular fitness, to determine whether then have a similar efficacy in affecting brain-derived neurotrophic factor levels. Methods: 12 untrained young males (aged 23.7 ± 1.8 years), participated in a randomized controlled cross-over trial. They underwent two different work-to-rest ratio high-intensity interval training protocols: high-intensity interval training 1 (30 min, 15 intervals of 1 min efforts at 85%-90% VO2max with 1 min of active recovery at 50%-60% VO2max) and HIIT2 (30 min, 10 intervals of 2 min efforts at 85%-90% VO2max with 1 min of active recovery at 50%-60% VO2max). Serum cortisol, brain-derived neurotrophic factor were collected at baseline, immediately following intervention, and 30 min into recovery for measurements using a Sandwich ELISA method, blood lactate was measured by using a portable lactate analyzer. Results: Our results showed that the similar serum brain-derived neurotrophic factor change in both high-intensity interval training protocols, with maximal serum brain-derived neurotrophic factor levels being reached toward the end of intervention. There was no significant change in serum brain-derived neurotrophic factor from baseline after 30 min recovery. We then showed that both high-intensity interval training protocols significantly increase blood lactate and serum cortisol compared with baseline value (high-intensity interval training p < 0.01; high-intensity interval training 2 p < 0.01), with high-intensity interval training 2 reaching higher blood lactate levels than high-intensity interval training 1 (p = 0.027), but no difference was observed in serum cortisol between both protocols. Moreover, changes in serum brain-derived neurotrophic factor did corelate with change in blood lactate (high-intensity interval training 1 r = 0.577, p < 0.05; high-intensity interval training 2 r = 0.635, p < 0.05), but did not correlate with the change in serum cortisol. Conclusions: brain-derived neurotrophic factor levels in untrained young men are significantly increased in response to different work-to-rest ratio of high-intensity interval training protocols, and the magnitude of increase is exercise duration independent. Moreover, the higher blood lactate did not raise circulating brain-derived neurotrophic factor. Therefore, given that prolonged exercise causes higher levels of cortisol. We suggest that the 1:1work-to-rest ratio of high-intensity interval training protocol might represent a preferred intervention for promoting brain health.

Label-free electrochemical aptasensor based on magnetic α-Fe2O3/Fe3O4 heterogeneous hollow nanorods for the detection of cancer antigen 125.

A label-free electrochemical aptasensor based on magnetic α-Fe2O3/Fe3O4 heterogeneous hollow nanorods was developed for the detection of cancer antigen 125 (CA125). Magnetic α-Fe2O3/Fe3O4 heterogeneous hollow nanorods were successfully prepared by the hydrolysis-calcination method, functionalized with polyethyleneimine (PEI), and modified with HAuCl4 to form magnetic α-Fe2O3/Fe3O4-Au nanocomposites with a layer of 5 nm gold nanoparticles (Au NPs) on the surface. The magnetic α-Fe2O3/Fe3O4-Au nanocomposites were used to fix the DNA-aptamer probe to amplify the current signal. The intensity of the current signal was proportional to the concentration of CA125, indicating that the sensor was a turn-on sensor. The linear range of the electrochemical aptasensor was 5-125 U/mL (R2 = 0.9975), and the limit of detection (LOD) was 2.99 U/mL. The electrochemical aptasensor exhibited favorable specificity, reproducibility, and stability. The analytical performance of the aptasensor in real serum samples was also investigated.

Construction of targeted delivery system for curcumin loaded on magnetic α-Fe2O3/Fe3O4 heterogeneous nanotubes and its apoptosis mechanism on MCF-7 cell.

In this work, the magnetic α-Fe2O3/Fe3O4 heterogeneous nanotubes were successfully prepared by solvent hydrothermal-controlled calcination method. The effects of additive concentration, hydrothermal temperature and time on morphology of products were investigated. The α-Fe2O3/Fe3O4 nanotubes with a saturation magnetization of 50 emu/g were prepared calcinated at 600 °C for 4 h using 0.8 g of glucose. Their average length, the outer and inner diameters were around 240 nm, 178 nm and 145 nm, respectively. The α-Fe2O3/Fe3O4 heterogeneous nanotubes coated with water-soluble liposome were applied for targeted delivery of curcumin. The release of curcumin inside the hollow structure of the nanocomposites could be triggered and effectively sustained represented a process of slow release. The encapsulation efficiency of curcumin in the α-Fe2O3/Fe3O4-CUR@LIP nanocomposites reached 82.1 ± 0.9%. MTT assays demonstrated that blank carriers had excellent biocompatibility and application of magnetic field significantly elevated the cytotoxicity of α-Fe2O3/Fe3O4-CUR@LIP nanocomposites on MCF-7 cell. Electrochemical experiment and Prussian blue staining indicated that the α-Fe2O3/Fe3O4@LIP nanocomposites could aggregate in cells to promote the internalization of curcumin. Magnetic α-Fe2O3/Fe3O4-CUR@LIP nanocomposites and curcumin enhanced the expression of reactive oxygen species in MCF-7 cells and induced apoptosis by fluorescence detection. Flow cytometry and western blot verified that the α-Fe2O3/Fe3O4@LIP nanocomposites under magnetic field enhanced cells late-apoptosis by adjusting the expression of apoptosis-related proteins.

Magnetically induced self-assembly DNAzyme electrochemical biosensor based on gold-modifiedα-Fe2O3/Fe3O4heterogeneous nanoparticles for sensitive detection of Ni2.

A magnetically induced self-assembly DNAzyme electrochemical biosensor based on gold-modifiedα-Fe2O3/Fe3O4heterogeneous nanoparticles was successfully fabricated to detect Nickel(II) (Ni2+). The phase composition and magnetic properties ofα-Fe2O3/Fe3O4heterogeneous nanoparticles controllably prepared by the citric acid (CA) sol-gel method were investigated in detail. Theα-Fe2O3/Fe3O4heterogeneous nanoparticles were modified by using trisodium citrate as reducing agent, and the magnetically induced self-assemblyα-Fe2O3/Fe3O4-Au nanocomposites were obtained. The designed Ni2+-dependent DNAzyme consisted of the catalytic chain modified with the thiol group (S1-SH) and the substrate chain modified with methylene blue (S2-MB). The MGCE/α-Fe2O3/Fe3O4-Au/S1/BSA/S2 electrochemical sensing platform was constructed and differential pulse voltammetry was applied for electrochemical detection. Under the optimum experimental parameters, the detection range of the biosensor was 100 pM-10µM (R2 = 0.9978) with the limit of detection of 55 pM. The biosensor had high selectivity, acceptable stability, and reproducibility (RSD = 4.03%).

Magnetic α-Fe2O3/Fe3O4 Heterostructure Nanorods: Fabrication and Cytotoxicity to A549 Cells.

The magnetic α-Fe2O3/Fe3O4 heterostructure nanorods were fabricated by an alcohol-solution direct combustion method. The influence of the calcination temperature on the composition and properties of the nanorods was investigated. When the calcination temperature was not greater than 400 °C, the magnetic α-Fe2O3/Fe3O4 heterostructure nanorods were obtained, and the saturation magnetization (Ms) of the magnetic α-Fe2O3/Fe3O4 heterostructure nanorods decreased with the calcination temperature increasing from 250 °C to 400 °C; when the calcination temperature was equal or greater than 450 °C, α-Fe2O3 nanorods were obtained. In addition, the effects of nanorods' concentration, nanorods' constituent, incubation time and magnetic field on A549 cytotoxicity were investigated. The cytotoxicity of the heterostructure nanorods appeared time-dependent and concentration-dependent, and the magnetic field could enhance the cytotoxicity of nanorods to A549.

Improved delivery system for celastrol-loaded magnetic Fe3O4/α-Fe2O3 heterogeneous nanorods: HIF-1α-related apoptotic effects on SMMC-7721 cell.

Fe3O4/α-Fe2O3 heterogeneous nanorods were prepared by a rapid combustion method with α-FeOOH nanorods as precursors. Fe3O4/α-Fe2O3 heterogeneous nanorods with a saturation magnetization of 33.2 emu·g-1 were obtained using 30 mL of absolute ethanol at a calcination temperature of 300 °C. Their average length was around 140 nm, and average diameter was about 20 nm. To improve the dispersion characteristics of the Fe3O4/α-Fe2O3 heterogeneous nanorods in aqueous solution, citric acid and PEG were applied to modify the nanorod surface via the Mitsunobu reaction. The results showed that the hydrodynamic size range of Fe3O4/α-Fe2O3/CA-PEG-celastrol was 250-500 nm, the surface potential was -15 mV, and the saturation magnetization was approximately 23 emu·g-1. The drug loading capacity of Fe3O4/α-Fe2O3/CA-PEG was larger than the non-PEG modified version. Fe3O4/α-Fe2O3/CA-PEG-celastrol had slow-release characteristics and was sensitive to changes in pH. Application of a magnetic field significantly promoted the inhibition of SMMC-7721 human liver cancer cell growth after treatment with Fe3O4/α-Fe2O3/CA-PEG-celastrol. Celastrol and Fe3O4/α-Fe2O3/CA-PEG-celastrol increased the production of reactive oxygen species in SMMC-7721 cells and promoted apoptosis and apoptosis-related proteins (p53, Bax, Bcl-2) were also changed. In addition, the expression of hypoxia-inducible factor 1α (HIF-1α) was enhanced. We may conclude that celastrol-loaded magnetic Fe3O4/α-Fe2O3 heterogeneous nanorods may be applied in the chemotherapy of human cancer with good biocompatibility and delivery.

Superparamagnetic α-Fe2O3/Fe3O4 Heterogeneous Nanoparticles with Enhanced Biocompatibility.

A novel type of magnetic α-Fe2O3/Fe3O4 heterogeneous nanoparticles was prepared via a facile solution combustion process with ferric nitrate and urea as raw materials, and they were characterized by XRD, SEM, TEM, and VSM techniques. The effects of the calcination temperature, the calcination time, the ratio of ferric nitrate and urea, and the heating rate on the relative content of Fe3O4 in the heterogeneous nanoparticles were investigated. The toxicity of α-Fe2O3/Fe3O4 heterogeneous nanoparticles to human hepatocytes L-02, the blood routine, and the histopathological section observation of mice were explored. The results showed that the ratio of ferric nitrate and urea was a key factor to affect the relative content of Fe3O4 in the heterogeneous nanoparticles. The calcination temperature and the calcination time had similar influences, and the corresponding calcination temperature and the calcination time were selected according to their own needs. The CCK8 results initially revealed that α-Fe2O3/Fe3O4 heterogeneous nanoparticles had no effect on cell viability when the concentration of the heterogeneous nanoparticles was less than 100 ng/mL, which suggested their excellent biocompatibility. At the same time, the tail vein administration concentration of 0.9 mg/kg had good biological safety.

Delivery of apigenin-loaded magnetic Fe2O3/Fe3O4@mSiO2 nanocomposites to A549 cells and their antitumor mechanism.

This study introduces a mesoporous magnetic nano-system for the delivery of apigenin (API). A targeted therapeutic drug delivery system was prepared based on Fe2O3/Fe3O4@mSiO2-HA nanocomposites. Magnetic Fe2O3/Fe3O4 heterogeneous nanoparticles were first prepared via the rapid-combustion process. The effects of solvent type, solvent volume, calcination temperature, and calcination time on the crystal size and magnetism of the Fe2O3/Fe3O4 heterogeneous nanoparticles were investigated. The mesoporous silica shell was deposited on the Fe2O3/Fe3O4 heterogeneous nanoparticles using an improved Stöber method. HA was exploited as the targeting ligand. The specific surface area of the Fe2O3/Fe3O4@mSiO2 nanocomposites was 369.6 m2/g, which is 19 times higher than that of the magnetic Fe2O3/Fe3O4 heterogeneous nanoparticle cores. Drug release properties from the Fe2O3/Fe3O4@mSiO2-HA nanocomposites were studied, and the result showed that API-loaded nano-system had sustained release effect. Prussian blue staining and electrochemical performance variation showed that an external magnetic field facilitated cell uptake of Fe2O3/Fe3O4@mSiO2-HA nanocomposites. MTT assays showed that the cell inhibition effect of API-Fe2O3/Fe3O4@mSiO2-HA was stronger than that of free API at the same drug dose under a magnetic field and Fe2O3/Fe3O4@mSiO2-HA nanocomposites showed good biocompatibility. Fluorescence imaging, flow cytometry, western blot, reactive oxygen species (ROS), Superoxide dismutase (SOD) and malondialdehyde (MDA) kits verified that the enhanced therapeutic action was due to the promotion of apoptosis, lipid peroxidation, and ferroptosis. The magnetic nano-system (Fe2O3/Fe3O4@mSiO2-HA) showed good magnetic targeting and active hyaluronic acid targeting, and has the potential to provide a targeted delivery platform for many antitumor drugs.

Using galactitol dehydrogenase coupled with water-forming NADH oxidase for efficient enzymatic synthesis of L-tagatose.

L-Tagatose, a promising building block in the production of many value-added chemicals, is generally produced by chemical routes with a low yield, which may not meet the increasing demands. Synthesis of l-tagatose by enzymatic oxidation of d-galactitol has not been applied on an industrial scale because of the high cofactor costs and the lack of efficient cofactor regeneration methods. In this work, an efficient and environmentally friendly enzymatic method containing a galactitol dehydrogenase for d-galactitol oxidation and a water-forming NADH oxidase for regeneration of NAD+ was first designed and used for l-tagatose production. Supplied with only 3 mM NAD+, subsequent reaction optimization facilitated the efficient transformation of 100 mM of d-galactitol into l-tagatose with a yield of 90.2 % after 12 h (obtained productivity: 7.61 mM.h-1). Compared with the current chemical and biocatalytic methods, the strategy developed avoids by-product formation and achieves the highest yield of l-tagatose with low costs. It is expected to become a cleaner and more promising route for industrial biosynthesis of l-tagatose.

Immobilization and Evaluation of Penicillin G Acylase on Hydroxy and Aldehyde Functionalized Magnetic α-Fe2O3/Fe3O4 Heterostructure Nanosheets.

Magnetic α-Fe2O3/Fe3O4 heterostructure nanosheets were fabricated via hydrothermal calcination. The activity of penicillin G acylase (PGA), which was covalently immobilized onto silica-decorated heterostructure nanosheets, achieved the highest activity of 387.03 IU/g after 18 h of incubation with 0.1 ml of PGA. In contrast, the activity of free PGA reached the highest level when the temperature was 45°C with a pH of 8.0. However, the activity of free PGA changed more dramatically than immobilized PGA as the relative conditions changed. Moreover, the Michaelis-Menten constant (Km) and reusability of immobilized PGA were also explored. The results showed that free PGA Km and maximum rate (Vmax) were 0.0274 M and 1.167 µl/min, respectively. Km and Vmax values of immobilized PGA were 0.1082 M and 1.294 µl/min, respectively. After 12 cycles of repetitive use, immobilized PGA remained approximately 66% of its initial activity, indicating that the PGA immobilized onto the heterostructure nanosheets showed better stability and reusability than free PGA.

Covalent immobilization and characterization of penicillin G acylase on magnetic Fe2O3/Fe3O4 heterostructure nanoparticles prepared via a novel solution combustion and gel calcination process.

In this work, magnetic Fe2O3/Fe3O4 heterostructure nanoparticles were prepared via a novel solution combustion and gel calcination process. The glutaraldehyde was cross-linked on Fe2O3/Fe3O4 heterostructure nanoparticles decorated silica. The prepared samples were characterized by TEM, EDS, XRD, VSM, SEM, XPS, TGA/DSC, BET measurement, Raman spectroscopy, Zeta potential, HR-TEM and FT-IR. The penicillin G acylase (PGA) was covalently immobilized on magnetic Fe2O3/Fe3O4@SiO2-CHO nanocomposites via the Schiff's reaction. Variations in the observed activities as a function of immobilization time and PGA concentration have been discussed, when immobilization time and concentration of PGA were 18 h and 0.2 mg·mL-1, the activity of immobilized PGA presented optimal values of 77.8 U·L-1 and 66.2 U·L-1. The effects of pH and temperature on enzyme activity were also evaluated, the activity of PGA at the temperature of 45 °C with buffer pH of 8 arrived at the highest lever. After 12 cycles of repetitive uses, the immobilized PGA still retained around 67% of initial activity. The research results indicated that PGA immobilized on magnetic Fe2O3/Fe3O4@SiO2-CHO nanocomposites showed excellent thermal stability, pH stability, and reusability compared with free enzyme.

Preparation of Magnetic Ni0.5Zn0.5Fe2O4/ZnO Nanocomposites and Their Photocatalytic Performances for Methylene Blue in Aqueous Solution.

Magnetic Ni0.5Zn0.5Fe2O4/ZnO-R (NZFO/ZnO-R) nanocomposites are prepared via the rapid combustion-coprecipitation process, and they are characterized by the Fourier Transform Infrared Spectroscopy (FTIR), the X-ray Diffraction (XRD), the Scanning Electron Microscopy (SEM), the Energy Dispersive X-ray Detector (EDX), the Specific Surface Area (BET), the UV-vis Diffuse Reflection Spectroscopy (DRS), and the Vibrating Sample Magnetometer (VSM). The photocatalytic activity of NZFO/ZnO-R nanocomposites is assessed in ultraviolet light (365 nm) by decoloration of methylene blue (MB). The results show that the magnetic NZFO/ZnO-0.2 nanocomposites consist of particles and rods. The size of particles is 18 nm. The width and length of rods are 66 nm and 198 nm, respectively. NZFO/ZnO-0.5 nanocomposites have better photocatalytic performance than that of NZFO, ZnO and NZFO/ZnO-R (R = 0.2, 0.3, 0.4, 0.6, or 0.7) from the results. Through careful investigation of influencing parameters (the amount of catalysts, pH and concentration of MB solution), the degradation efficiency of MB is closely connected with the transparency of solution and surface charge of catalysts. The enhanced photocatalytic activity of NZFO/ZnO-0.5 nanocomposites can be ascribed to the matching band positions between ZnO and NZFO, which results in a low recombination between the photogenerated electron-hole pairs. The possible mechanism is proposed for the improved ultraviolet photocatalytic activity of NZFO/ZnO-0.5 nanocomposites.

Fabrication of Magnesium Ferrites for Enormous Adsorbance of Neutral Red and Their Electrochemical Properties.

Magnetic magnesium ferrite nanoparticles were fabricated via the ethanol-assisted solution combustion and gel calcination route. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometer, Brunauer-Emmett-Teller (BET) surface area measurement, vibrating sample magnetometer (VSM) and X-ray diffraction (XRD) were applied to characterize magnetic magnesium ferrite nanoparticles which were prepared under the condition of 20 mL absolute alcohol and calcined at 600 °C for two hours. The results showed that the nanoparticles were spinel structure with the saturation magnetization of 183 emu·g-1, the average grain size of 52 nm, the specific surface area of 33.2 m² · g-1. In addition, the electrochemical property and adsorption mechanism of neutral red (NR) onto the magnetic MgFe2O4 nanoparticles were investigated. The adsorption results were conformed to the pseudo-second-order adsorption kinetic and Temkin model, which implied that the multimolecular layer chemical adsorption had occurred. Moreover, the pH had little effect on the process of the adsorption, and the value of the magnetic magnesium ferrite nanoparticles for NR adsorption was up to 555 mg · g-1.

Immobilization and characterization of cellulase on hydroxy and aldehyde functionalized magnetic Fe2O3/Fe3O4 nanocomposites prepared via a novel rapid combustion process.

In this work, magnetic Fe2O3/Fe3O4 nanocomposites were prepared via a novel rapid combustion process. The silica was precipitated on the surface of Fe2O3/Fe3O4 nanocomposites. The silica-coated magnetic nanocomposites were cross-linked with glutaraldehyde, on which cellulase was covalently immobilized. The morphology, composition, and property of the prepared nanomaterials were characterized by the scanning electron microscopy (SEM), the energy dispersive spectrometry (EDS), the X-ray diffraction (XRD), the vibrating sample magnetometer (VSM), and the Fourier transform infrared (FTIR) spectroscopy. The immobilization conditions were optimized by varying operating parameters and determined to be 0.05 mL of 0.5% cellulase solution for 2 h. The catalytic stabilities of the immobilized cellulase were evaluated. The results showed that the immobilized cellulases performed higher apparent activity at pH 4.5 and exhibited good thermal stability compared with their free counterparts. The Michaelis-Menten equation showed that Km and Vmax of free cellulase were 3.46 mol·L-1 and 0.53 mol·min-1, respectively. The immobilized cellulase had higher Km and Vmax (18.99 mol·L-1 and 0.59 mol·min-1). The retained activity of the immobilized cellulase maintained over 71% of the initial activity after being used for five cycles.