Fe3O4 magnetic nanoparticles as peroxidase mimetics and their applications in H2O2 and glucose detection

Artificial enzyme mimetics are a current research interest because natural enzymes bear some serious disadvantages, such as their catalytic activity can be easily inhibited and they can be digested by proteases. A very recently study reported by Yan et al. has proven that Fe(3)O(4) magnetic nanoparticles (MNPs) exhibit an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, though MNPs are usually thought to be biological and chemical inert (Gao, L. Z.; Zhuang, J.; Nie, L.; Zhang, J. B.; Zhang, Y.; Gu, N.; Wang, T. H.; Feng, J.; Yang, D. L.; Perrett, S.; Yan, X. Y. Nat. Nanotechnol. 2007, 2, 577-583). In the present work, we just make use of the novel properties of Fe(3)O(4) MNPs as peroxidase mimetics reported by Yan et al. to detect H(2)O(2). The Fe(3)O(4) MNPs were prepared via a coprecipitation method. The as-prepared Fe(3)O(4) MNPs were then used to catalyze the oxidation of a peroxidase substrate 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) by H(2)O(2) to the oxidized colored product (see eq 1) which provides a colorimetric detection of H(2)O(2). As low as 3 x 10(-6) mol/L H(2)O(2) could be detected with a linear range from 5 x 10(-6) to 1 x 10(-4) mol/L via our method. More importantly, a sensitive and selective method for glucose detection was developed using glucose oxidase (GOx) and the as-prepared Fe(3)O(4) MNPs. The detection platforms for H(2)O(2) and glucose developed in the present work not only further confirmed that the Fe(3)O(4) MNPs possess intrinsic peroxidase-like activity but also showed great potential applications in varieties of simple, robust, and easy-to-make analytical approaches in the future.     

Magnetic and gold-coated magnetic nanoparticles as a DNA sensor

In this study, we report the chemical synthesis and functionalization of magnetic and gold-coated magnetic nanoparticles and the immobilization of single-stranded biotinylated oligonucleotides onto these particles. Selected sequences specific to the BRCA1 gene were used as a test platform. The binding of oligonucleotides to these particles was achieved through a streptavidin-biotin bridge via a carbodiimide activation protocol. Particle size and oligonucleotide attachment were confirmed by transmission electron microscopy; oligonucleotide binding was characterized by Fourier transform infrared spectroscopy and hybridization confirmed by fluorescence emission from the fluorophore attached to the target oligonucleotide strand. The rate of hybridization was measured using a spectrofluorometer and a microarray scanner. The rate of hybridization of oligonucleotides bound to the synthesized particles depends on the inorganic support material and its surface chemistry. The rate of hybridization increased concomitantly with the concentration of the probe and the target in the reaction medium. Furthermore, exposure of probe and target oligonucleotide to a combination of target and noncomplementary DNA strand reduced the rate of hybridization, possibly because of steric crowding in the reaction medium and cross-linking between reacting oligonucleotides and the noncomplementary strands. The study undertaken opens several possibilities in bioconjugate attachment to functionalized iron and iron nanocomposite structures for controlled manipulation and handling using magnetic fields.     

A new immobilized glucose oxidase using SiO2 nanoparticles as carrier

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.     

Facile one-pot synthesis of iron oxide nanoparticles cross-linked magnetic poly(vinyl alcohol) gel beads for drug delivery

In this paper, a facile one-pot strategy for scalable synthesis of robust magnetic poly(vinyl alcohol) (mPVA) gel beads is developed. Through dropwise addition of mixed aqueous solution of iron salts and PVA solution into alkaline (e.g., ammonia, NaOH, and KOH) solution, mPVA gel beads with uniform size and excellent superparamagnetic property can be fabricated based on the simultaneous formation of magnetic iron oxide nanoparticles (MIONs) and cross-link of PVA chains. Moreover, this approach can be extended to prepare dual- or multiresponsive gel beads through simply adding functional fillers into PVA solution (e.g., mPVA-PNIPAM gel beads that possess both magnetic and temperature responsibilities can be readily prepared by adding temperature responsive poly(N-isopropylacrylamide) (PNIPAM) into PVA solution). It is found that that the obtained mPVA gel beads exhibit high drug loading level (e.g., above 70%) after the treatment of freezing-thawing. Drug release experiments reveal that the drug release rate and amount of the mPVA gel beads can be tuned by operating the external magnetic field and adjusting the concentration of iron oxide nanoparticles and temperature (for mPVA-PNIPAM gel beads). The present work is of interest for opening up enormous opportunities to make full use of magnetic gel beads in drug delivery and other applications, because of their facile availability, cost-effective productivity, and tunable drug release performance.     

磁性纳米颗粒作为基因载体的研究发展概况

磁性纳米颗粒作为非病毒基因载体介导的基因转染(即磁性转染)是基因治疗中极具运用前景的技术之一。主要介绍了磁性纳米颗粒的种类和性质,介导基因转染的最新研究进展,在细胞内的定位和动态过程,面临的问题以及将来的发展前景。     

Amperometric glucose sensor based on enhanced catalytic reduction of oxygen using glucose oxidase adsorbed onto core-shell Fe3O4@silica@Au magnetic nanoparticles

Monodisperse Fe₃O₄ magnetic nanoparticles (NPs) were prepared under facile solvothermal conditions and successively functionalized with silica and Au to form core/shell Fe₃O₄@silica@Au NPs. Furthermore, the samples were used as matrix to construct a glucose sensor based on glucose oxidase (GOD). The immobilized GOD retained its bioactivity with high protein load of 3.92 × 10^? 9 mol·cm^? 2, and exhibited a surface-controlled quasi-reversible redox reaction, with a fast heterogeneous electron transfer rate of 7.98 ± 0.6 s^? 1. The glucose biosensor showed a broad linear range up to 3.97 mM with high sensitivity of 62.45 μA·mM^? 1 cm^? 2 and fast response (less than 5 s).     

A CMOS rotary encoder using magnetic sensor arrays

A new type of small magnetic rotary encoder is presented. The device detects the magnetic field of a permanent magnet attached to the end of the rotating shaft using complementary metal-oxide semiconductor (CMOS) magnetic sensors [magnetic field effect transistor (MAGFET) arrays] set in a square arrangement. The sensor array is integrated onto a CMOS chip along with angle-detection circuits, leading to the realization of a compact, cost-effective rotary encoder. A prototype sensor chip with dimensions of 4.3/spl times/4.3 mm/sup 2/ is shown to provide error as low as 3.5/spl deg/ without offset calibration and 0.36/spl deg/ with offset calibration, based on an angle calculation method with mean square estimation. This result shows that the CMOS rotary encoder can achieve resolution of 10 bits/rotation at the cost of calibration.     

Bacterial inactivation using silver-coated magnetic nanoparticles as functional antimicrobial agents

The ability for silver nanoparticles to function as an antibacterial agent while being separable from the target fluids is important for bacterial inactivation in biological fluids. This report describes the analysis of the antimicrobial activities of silver-coated magnetic nanoparticles synthesized by wet chemical methods. The bacterial inactivation of several types of bacteria was analyzed, including Gram-positive bacteria ( Staphylococcus aureus and Bacillus cereus ) and Gram-negative bacteria ( Pseudomonas aeruginosa , Enterobacter cloacae , and Escherichia coli ). The results have demonstrated the viability of the silver-coated magnetic nanoparticles for achieving effective bacterial inactivation efficiency comparable to and better than that of silver nanoparticles conventionally used. The bacteria inactivation efficiency of our silver-coated MnZn ferrite (MZF@Ag) nanoparticles was also determined for blood platelets samples, demonstrating the potential of utilization in inactivating bacterial growth in platelets prior to transfusion to ensure blood product safety, which also has important implications for enabling the capability of effective separation, delivery, and targeting of the antibacterial agents.     

Preparation of silica–silver heterogeneous nanocomposite particles by one-pot preparation strategy using polyol process: Size-controlled immobilization of silver nanoparticles

The size-controlled immobilization of silver nanoparticles onto the silica surface was carried out through one-pot process involving polyol process for the first time. Thiol groups were employed as a chemical protocol to make a binding bridge between silver nanoparticle and silica surface. The size of immobilized silver nanoparticles was controlled by reaction temperature and time at two different concentrations of silver nitrate: 1000 and 10,000 ppm. This one-pot process involving polyol process can simplify the conventional complex reaction process to control the size of immobilized metal nanoparticles. Also, this research can contribute to the immobilization of the other metals onto the inorganic supports and to the control of the size of immobilized metal particles.     

A sensitive magnetic field sensor using BPSCCO thick film

A highly sensitive magnetic sensor operating at liquid nitrogen temperature and based on BPSCCO screen-printed thick film, is reported. The sensor resistance for an applied magnetic field of 100 ×10⁻⁴ T (100 gauss) exhibits an increase by 360% of its value in zero field at 77.4 K. The performance of the sensor in presence of magnetic field, the hysteretic features and the effect of thermal cycling, has been discussed.     

Forward osmosis desalination using pectin-coated magnetic nanoparticles as a draw solution

Clean Technologies and Environmental Policy - In this study, magnetic Fe3O4 nanoparticles and pectin-coated magnetic Fe3O4 nanoparticles were used as a potential draw solution in forward osmosis...     

Electrochemical sensor for organophosphate pesticides and nerve agents using zirconia nanoparticles as selective sorbents

An electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of the strong affinity of zirconia for the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5-100 ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 3 ng/mL and good precision (RSD = 5.3%, n = 10). The detection limit was improved to 1 ng/mL by using 10-min adsorption time. The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analysis of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.     

Substrate-specific modifications on magnetic iron oxide nanoparticles as an artificial peroxidase for improving sensitivity in glucose detection

Magnetic iron oxide nanoparticles (MION) were recently found to act as a peroxidase with intrinsic advantages over natural counterparts. Their limited affinity toward catalysis substrates, however, dramatically reduces their utility. In this paper, some effective groups were screened out and conjugated on MION as substrate-specific modifications for improving MION's affinity to substrates and hence utility. Nanoparticles of four different superficial structures were synthesized and characterized by TEM, size, zeta potential and SQUID, and assayed for peroxidase activity. Glucose detection was selected as an application model system to evaluate the bonus thereof. Catalysis was found to follow Michaelis-Menten kinetics. Sulfhydryl groups incorporated on MION (SH-MION) notably improve the affinity toward a substrate (hydrogen peroxide) and so do amino groups (NH?-MION) toward another substrate, proved by variation in the determined kinetic parameters. A synergistically positive effect was observed and an apparently elevated detection sensitivity and a significantly lowered detection limit of glucose were achieved when integrated with both sulfhydryl and amino groups (SH-NH?-MION). Our findings suggest that substrate-specific surface modifications are a straightforward and robust strategy to improve MION peroxidase-like activity. The high activity extends magnetic nanoparticles to wide applications other than glucose detection.     

Ultrasensitive electrochemical immunosensor for clinical immunoassay using thionine-doped magnetic gold nanospheres as labels and horseradish peroxidase as enhancer

A new signal amplification strategy based on thionine (TH)-doped magnetic gold nanospheres as labels and horseradish peroxidase (HRP) as enhancer holds promise to improve the sensitivity and detection limit of the immunoassay for carcinoembryonic antigen (CEA), as a model protein. This immunoassay system was fabricated on a carbon fiber microelectrode (CFME) covered with a well-ordered anti-CEA/protein A/nanogold architecture. The reverse micelle method was initially used for the preparation of TH-doped magnetic gold nanospheres (nanospheres), and the synthesized nanospheres were then labeled on HRP-bound anti-CEA as a secondary antibody (bionanospheres). Sandwich-type protocol was successfully introduced to develop a new high-efficiency electrochemical immunoassay with the labeled bionanospheres toward the reduction of H2O2. Under optimized conditions, the linear range of the proposed immunoassay without HRP as enhancer was 1.2-125 ng/mL CEA, whereas the assay sensitivity by using HRP as enhancer could be further increased to 0.01 ng/mL with the linear range from 0.01 to 160 ng/mL CEA. The developed immunoassay method showed good precision, high sensitivity, acceptable stability and reproducibility, and could be used for the detection of real samples with consistent results in comparison with those obtained by the enzyme-linked immunosorbent assay (ELISA) method.     

The effect of CFO nanoparticles on magnetic and erosion-corrosion behavior of CFO@Ni-P nanocomposite coating

Cobalt ferrite nanoparticles (CFO-NPs) were used in electroless Ni–P solution to form a Ni-P-CoFe₂O₄ composite coating (CFO@Ni-P) on copper substrate. CFO-NPs with average size of 164 nm were synthetized using solution combustion method and the size of the particles was reduced to 105 nm and 78 nm, through mechanical milling. These nanoparticles were then added to Ni-P bath to form a composite coating. Investigation of morphology, corrosion resistance, the erosion-corrosion resistance, and magnetic properties of the samples conducted. It is revealed that, addition of nanoparticles with average size of 164 nm and concentration of 2 g/l, causes an increase corrosion and tribocorrosion properties of the coating. Cobalt ferrite nanoparticles participation in the coating causes appearance of a remnant magnetization in the composite coating, which reduces with decreasing CFO granular size.     

Removal of cationic dyes from aqueous solution using magnetic multi-wall carbon nanotube nanocomposite as adsorbent

A magnetic multi-wall carbon nanotube (MMWCNT) nanocomposite was synthesized and was used as an adsorbent for removal of cationic dyes from aqueous solutions. The MMWCNT nanocomposite was composed of commercial multi-wall carbon nanotubes and iron oxide nanoparticles. The properties of this magnetic adsorbent were characterized by scanning electron microscopy, X-ray diffraction and BET surface area measurements. Adsorption characteristics of the MMWCNT nanocomposite adsorbent were examined using methylene blue, neutral red and brilliant cresyl blue as adsorbates. Experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of adsorption dosage and solution pH values on the removal of cationic dyes. Kinetic data were well fitted by a pseudo second-order model. Freundlich model was used to study the adsorption isotherms. The prepared MMWCNT adsorbent displayed the main advantage of separation convenience compared to the present adsorption treatment.     

Spongiform immobilization architecture of ionotropy polymer hydrogel coentrapping alcohol oxidase and horseradish peroxidase with octadecylsilica for optical biosensing alcohol in organic solvent

An organic-phase optical alcohol biosensor consisting of alcohol oxidase and horseradish peroxidase coimmobilized in a spongiform hydrogel matrix of hydroxethyl carboxymethyl cellulose, an adduct of 3-methoxy-4-ethoxy benzaldehyde, 4-tert-butylpyridinium acetohydrazone, silica gel particles, and octadecylsilica particles in conjunction with an optical oxygen transducer has been successfully fabricated. The novel enzyme entrapment structure was mainly characterized with desirable solvent permeability, high efficiency of mass transfer for reactants, and good accessibility and stability of the immobilized enzymes. The biosensor could work in water-miscible solvent such as a solvent mixture of acetonitrile and phosphate aqueous buffer, as well as hydrophobic organic solvent such as n-hexane. The biosensor had the highest sensitivity to methanol in both solvent systems. Under the stop-flow mode, the biosensor had the analytical working ranges from 80 microM to 90 mM methanol in n-hexane and 0.10 to 90 mM methanol in acetonitrile/buffer. When the biosensor functioned in n-hexane, it could take benzaldehyde as an alcohol substrate and was free from any pH disturbance. In the presence of coimmobilized horseradish peroxidase, the operational life of the biosensor was 60 assays and the shelf life was longer than two weeks. The biosensor has been satisfactorily applied to the determination of methanol in commercial gasoline-methanol blend samples.     

A facile one-pot hydrothermal synthesis of cobalt sulfide nanospheres integrated with graphene nanocomposite as electrode material for high-performance supercapacitors

Journal of Materials Science: Materials in Electronics - Transition metal chalcogenides have fascinating characteristics are considered as electrode materials for high-performance energy storage...     

Preparation of nanocomposite for optical application using ZnTe nanoparticles and a zero-birefringence polymer

Surface-modified ZnTe nanoparticles were mixed in a zero-birefringence polymer matrix. Transmission electron microscopy images revealed that aggregates of ZnTe nanoparticles with a diameter of ∼20 nm were uniformly dispersed in the polymer. The transmittance of ZnTe nanocomposites rapidly decreased at wavelengths shorter than the critical wavelength corresponding to the band gap of ZnTe nanoparticles, an effect which became significant as the volume fraction of particles increased. In this way, the optical characteristic of ZnTe nanoparticles was added to the polymer. The intrinsic zero-birefringence was confirmed in the heat-drawn ZnTe nanocomposites. As the ZnTe nanocomposites were left in air, a lowering of transmittance was observed. This was due to the oxidation of Zn and the resultant deposition of Te in the ZnTe nanocomposite, as the light absorption of Te is significant. The formation of oxygen non-permeable SiO₂ films onto the ZnTe nanocomposite by the sol-gel method was useful in preventing oxidation so that the decrement of transmittance decreased from 47.2% to 14.9% at 530 nm near the ZnTe band gap.     

Fe2MoO4 magnetic nanocomposite modified screen printed graphite electrode as a voltammetric sensor for simultaneous determination of nalbuphine and diclofenac

Journal of Materials Science: Materials in Electronics - This study applied screen printed graphite electrode (SPGE) modified with the Fe2MoO4 magnetic nanocomposite for simultaneously determining...