A novel amperometric immunosensor based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles/chitosan composite film for determination of ferritin

A novel amperometric immunosensor was developed by immobilizing ferritin antibody (FeAb) on the surface of Fe₃O₄ magnetic nanoparticles/chitosan composite film modified glassy carbon electrode (GCE). This material combined the advantages of inorganic Fe₃O₄ nanoparticles with the organic polymer chitosan. The stepwise assembly procedure of the immunosensor was characterized by means of differential pulse voltammetry (DPV) and ac impedance. The K₃Fe(CN)₆/K₄Fe(CN)₆ was used as a marker to probe the interface and to determinate ferritin. The factors that could influence the performance of the resulting immunosensor were studied in detail. After the immunosensor was incubated with ferritin for 32 min at 35 °C, the DPV current decreased linearly with the logarithm of ferritin concentration in the range from 20 to 500 ng mL⁻¹ with a correlation coefficient of 0.995 and a detection limit of 7.0 ng mL⁻¹. This immunosensor was used to analyze ferritin in human serum samples. The analytical results showed that the developed immunoassay was comparable with the radioimmunoassay (RIA), and the studied immunosensor exhibited good accuracy, high sensitivity, and long-term stability for 3 weeks, which implies a promising alternative approach for detecting ferritin in clinical diagnosis.     

Amperometric Immunosensor Based on L-Cysteine/Gold Colloidal Nanoparticles for Carbofuran Detection

In this study, anti-carbofuran monoclonal antibodies (Ab) were immobilized onto a gold electrode surface modified with multilayers of L-cysteine and gold colloidal nanoparticles (GNPs). Furthermore, horseradish peroxidase (HRP) as enzyme membrane was used for blocking unspecific sites and amplifying signal. The conformational properties of the immunosensor were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The concentration of antibody solution, pH of working buffer and incubation time were studied in detail for optimization of analytical performance. Under optimal conditions, the variation of current response was proportional to the concentration of carbofuran which ranged from 0.01 ng/mL to 50 ng/mL with a correlation coefficient of 0.9912. The detection limit was 0.01 ng/mL (S/N = 3). The proposed immunosensor exhibited good reproducibility and stability and it can be used for the rapid detection of carbofuran pesticide.     

Preparation of a novel Fe3O4/graphene oxide hybrid for adsorptive removal of methylene blue from water

In this work, a novel Fe₃O₄/graphene oxide (GO) hybrid was prepared and its removal ability of cationic methylene blue dye from water was investigated. To improve the dispersability of Fe₃O₄/GO hybrid in water, GO was first modified by polyethylene glycol (PEG) via a click approach before deposition of Fe₃O₄ nanoparticles onto its surface. The successful modification of GO surface and the deposition of Fe₃O₄ nanoparticles were confirmed by transmission electron microscopy directly. The saturation magnetization of the resultant Fe₃O₄/GO hybrid is 7.8 eum/g. The adsorption capacities of Fe₃O₄/GO hybrid for methylene blue at 35 and 60°C were as high as 96.05 and 120.05 mg/g, respectively. Moreover, the Langmuir, Freundlich, and Temkin models are used to investigate the isothermal adsorption behavior of Fe₃O₄/GO hybrid.     

Preparation of Fe3O4@C@CNC multifunctional magnetic core/shell nanoparticles and their application in a signal-type flow-injection photoluminescence immunosensor

We describe here the preparation of carbon-coated Fe₃O₄ magnetic nanoparticles that were further fabricated into multifunctional core/shell nanoparticles (Fe₃O₄@C@CNCs) through a layer-by-layer self-assembly process of carbon nanocrystals (CNCs). The nanoparticles were applied in a photoluminescence (PL) immunosensor to detect the carcinoembryonic antigen (CEA), and CEA primary antibody was immobilized onto the surface of the nanoparticles. In addition, CEA secondary antibody and glucose oxidase were covalently bonded to silica nanoparticles. After stepwise immunoreactions, the immunoreagent was injected into the PL cell using a flow-injection PL system. When glucose was injected, hydrogen peroxide was obtained because of glucose oxidase catalysis and quenched the PL of the Fe₃O₄@C@CNC nanoparticles. The here proposed PL immunosensor allowed us to determine CEA concentrations in the 0.005–50 ng?·?mL^-1 concentration range, with a detection limit of 1.8 pg?·?mL^-1.

Fe3O4 MNPs-DETA/Benzyl-Br3: A new magnetically reusable catalyst for the oxidative coupling of thiols

We report a new strategy to immobilize a bromine source on the surface of magnetic Fe₃O₄ nanoparticles (Fe₃O₄ MNPs-DETA/Benzyl-Br₃) leading to a magnetically recoverable catalyst, which exhibits high catalytic efficiency in oxidative coupling of thiols to the disulfides (89–98%). The Fe₃O₄ MNPs-DETA/Benzyl-Br₃ catalyst was fabricated by anchoring 3-chloropropyltrimethoxysilane (CPTMS) on magnetic Fe₃O₄ nanoparticles, followed with N-benzylation and reaction with bromine in tetrachloridecarbon. The resulting nanocomposite was analyzed by a series of characterization techniques such as FT-IR, SEM, TGA, VSM and XRD. The catalyst could be recovered via magnetic attraction and could be recycled at least 5 times without appreciable decrease in activity.     

Sensitive electrochemical immunoassay for chlorpyrifos by using flake-like Fe3O4 modified carbon nanotubes as the enhanced multienzyme label

A highly sensitive electrochemical immunoassay of chlorpyrifos (CPF) was developed by using a biocompatible quinone-rich polydopamine nanospheres modified glass carbon electrode as the sensor platform and multi-horseradish peroxidase-flake like Fe₃O₄ coated carbon nanotube nanocomposites as the signal label. Due to the quinone-rich polydopamine nanospheres, the platform exhibited excellent fixing capacity by simple coating of sticky polydopamine nanospheres and subsequent oxidization. By coprecipitation of Fe³⁺ and Fe²⁺ on polydopamine modified carbon nanotubes (CNTs) with the aid of ethylene glycol (EG), the flake-like Fe₃O₄ coated CNTs (CNTs@f-Fe₃O₄) were synthesized and chosen as the carrier of multi-enzyme label due to the high loading of secondary antibody (Ab₂) and horseradish peroxidase (HRP) and also the peroxidase-mimic activity of Fe₃O₄. Under the optimum conditions, the immunosensor can detect CPF over a wide range with a detection limit of 6.3 pg/mL. Besides, the high specificity, reproducibility and stability of the proposed immunosensor were also proved. The preliminary application in real sample showed good recoveries, indicating it holds promise for fast analysis of CPF in aquatic environment.     

A Novel Magnetism‐assisted Electrochemical Immunosensor with Sub‐Picomolar Sensitivity

A novel electrochemical immunosensor based on a magnetic glassy carbon electrode (MGCE) was developed for the quantitative determination of human immunoglobulin G (IgG). The immunosensing interface was fabricated by initially depositing silver nanoparticles on the MGCE surface and then immobilizing anti‐human IgG antibodies via the magnetic force between MGCE and Fe₃O₄ nanoparticles. The antibodies were covalently bonded to the amine‐functionalized Fe₃O₄ nanoparticles. Under optimal conditions, the magnetism‐assisted immunosensor exhibited a wide linear range from 0.1 pg/mL to 1.0 µg/mL with the detection limit of 0.05 pg/mL. Furthermore, the immunosensor displayed the advantages of good reproducibility and satisfactory stability.     

叶酸对磁性Fe_3O_4纳米粒子的表面修饰

以FeCl3·6H2O作为单一铁源,1,6-己二胺作为胺化试剂,利用无模板的溶剂热方法制备了胺基功能化的磁性Fe3O4纳米粒子,并利用其键合叶酸分子,制备出表面修饰了叶酸的磁性Fe3O4复合纳米粒子。利用傅里叶变换红外光谱仪、X-射线衍射仪、透射电镜、差热-热重分析仪和振动样品磁强计对所得纳米粒子的形貌、粒径、化学组成和磁性能进行了表征。结果表明,叶酸分子通过化学键牢固键合在磁性纳米Fe3O4粒子表面,叶酸修饰的复合纳米粒子仍然具有良好的磁性能。     

基于一维DNA组装磁性纳米探针的夹心型安培免疫传感器研究

采用Fe3O4(核)/ZrO2(壳)纳米磁珠(ZMPs)标记待测物识别抗体,并用HRP酶封闭和DNA链接,建立了一类新型的"珠链状"一维磁性纳米探针制备方法。将甲胎蛋白(AFP)一抗固定于纳米金修饰的玻碳电极表面,构建了免疫电极(GCE?AFP Ab1)。基于该电极和上述合成探针,通过双抗体夹心法测定免疫产物上HRP酶对过氧化脲(CP)氧化对苯二酚反应的催化电流,研制了一类基于一维纳米结构组装的夹心型安培免疫传感器。研究表明:此一维纳米结构探针不仅大大增加了酶在电极表面的富集量,成倍扩增了催化电流,显著提高了传感器的灵敏度,而且易于通过外磁场与背景液可控分离,简化了分析步骤,并提高了结果的重复性。此传感器对AFP检测的线性范围为0.01~25 mg/L;检出限达4 ng/L(3σ),并被用于人血清中痕量AFP的测定,结果满意。     

Fabrication of N-(Amino-Ethyl)-Amino-Propyl Functionalized Magnetite Nanoparticles for Oil–Water Separation of Wastewater From Tertiary Oil Recovery

N-(amino-ethyl)-amino-propyl trimethoxy silane (AEAPTMS) is used to modify Fe₃O₄ with a one-pot coprecipitation method. Powder X-ray diffraction measurements show the spinel structure of magnetite nanoparticles. A high positive charge of +33.96 mV was obtained on the surfaces of modified magnetic nanoparticles, with the diameter ranging from 6.5 to 22.5 nm. The modified Fe₃O₄ was first applied to the treatment of wastewater from tertiary oil recovery. The obtained results indicated that the oil removal rate increased with the dosage of modified Fe₃O₄ and slightly increased with the separation time. The mechanism of modified Fe₃O₄ toward wastewater from tertiary oil recovery was attributed to the electrostatic interaction between negatively charged microemulsion oil in wastewater and the positively charged surfaces of magnetic nanoparticles.     

Synthesis of orientedly bioconjugated core/shell Fe3O4@Au magnetic nanoparticles for cell separation

Orientedly bioconjugated core/shell Fe₃O₄@Au magnetic nanoparticles were synthesized for cell separation. The Fe₃O₄@Au magnetic nanoparticles were synthesized by reducing HAuCl₄ on the surfaces of Fe₃O₄ nanoparticles, which were further characterized in detail by TEM, XRD and UV-vis spectra. Anti-CD3 monoclonal antibody was orientedly bioconjugated to the surface of Fe₃O₄@Au nanoparticles through affinity binding between the Fc portion of the antibody and protein A that covalently immobilized on the nanoparticles. The oriented immobilization method was performed to compare its efficiency for cell separation with the non-oriented one, in which the antibody was directly immobilized onto the carboxylated nanoparticle surface. Results showed that the orientedly bioconjugated Fe₃O₄@Au MNPs successfully pulled down CD3⁺ T cells from the whole splenocytes with high efficiency of up to 98.4%, showing a more effective cell-capture nanostructure than that obtained by non-oriented strategy. This developed strategy for the synthesis and oriented bioconjugation of Fe₃O₄@Au MNPs provides an efficient tool for cell separation, and may be further applied to various fields of bioanalytical chemistry for diagnosis, affinity extraction and biosensor.     

A Renewable Potentiometric Immunosensor Based on Fe3O4 Nanoparticles Immobilized Anti‐IgG

A renewable potentiometric immunosensor for detection of immunoglobulin G (IgG) has been developed by magnetic force attraction of Fe₃O₄ nanoparticles immobilized goat‐anti‐human IgG antibody. For preparing sensitive film of the sensor, cysteine was bonded on the nano‐Fe₃O₄ particles surface. The cysteine functionalized magnetic nanoparticles was attracted on a solid paraffin carbon paste electrode surface to covalently immobilize of anti‐immunoglobulin G (anti‐IgG) by employing a conventional glutaraldehyde‐crosslinking method. The immunosensor showed a specific response to human immunoglobulin G in the range of 0.1–1.2 ng/mL with a detection limit of 0.023 ng/mL. The immunosensor based on the magnetic nanoparticles was made easily by this method. It can be used expediently, renewed easily and low‐cost relatively. The renewable potentiometric immunosensor with better stability and higher sensitivity can be employed extensively in clinical diagnosis, monitoring of disease and environmental studies and etc.     

ATP适体接枝Fe3O4纳米粒子的制备及化学发光酶检测应用

制备了油酸修饰的Fe₃O₄纳米粒子,利用盐酸多巴胺对其表面进行氨基化改性,制得水分散性良好的Fe₃O₄纳米粒子,用X射线衍射、透射电镜、傅里叶变换红外光谱仪、振动样品磁强计和紫外-可见吸收光谱进行表征。随后,将氨基修饰的三磷酸腺苷（ATP）适体接枝到Fe₃O₄纳米粒子上,结合荧光素酶化学发光法进行ATP的定量检测,并应用于市售酸奶中乳酸菌ATP含量的检测,其灵敏度高、重现性好。各项实验结果表明所制备的Fe₃O₄纳米粒子是一种分散性好、易分离的载体,其粒径均一、稳定、磁性强、与适体结合性能好,拓展了Fe₃O₄纳米粒子在分析检测领域的应用。     

ATP适体接枝Fe_3O_4纳米粒子的制备及化学发光酶检测应用

制备了油酸修饰的Fe_3O_4纳米粒子,利用盐酸多巴胺对其表面进行氨基化改性,制得水分散性良好的Fe_3O_4纳米粒子,用X射线衍射、透射电镜、傅里叶变换红外光谱仪、振动样品磁强计和紫外-可见吸收光谱进行表征。随后,将氨基修饰的三磷酸腺苷(ATP)适体接枝到Fe_3O_4纳米粒子上,结合荧光素酶化学发光法进行ATP的定量检测,并应用于市售酸奶中乳酸菌ATP含量的检测,其灵敏度高、重现性好。各项实验结果表明所制备的Fe_3O_4纳米粒子是一种分散性好、易分离的载体,其粒径均一、稳定、磁性强、与适体结合性能好,拓展了Fe_3O_4纳米粒子在分析检测领域的应用。     

Chitosan–iron oxide nanobiocomposite based immunosensor for ochratoxin-A

The rabbit immunoglobulin antibodies (IgGs) have been immobilized onto nanobiocomposite film of chitosan (CH)–iron oxide (Fe₃O₄₎ nanoparticles prepared onto indium–tin oxide (ITO) electrode for detection of ochratoxin-A (OTA). Excellent film forming ability and availability of –NH₂ group in CH and affinity of surface charged Fe₃O₄ nanoparticles for oxygen support the immobilization of IgGs. Differential pulse voltammettry (DPV) studies indicate that Fe₃O₄ nanoparticles provide increased electroactive surface area for loading of IgGs and improved electron transport between IgGs and electrode. IgGs/CH–Fe₃O₄ nanobiocomposite/ITO immunoelectrode exhibits improved characteristics such as low detection limit (0.5 ng dL⁻¹), fast response time (18 s) and high sensitivity (36 μA/ng dL⁻¹ cm⁻²) with respect to IgGs/CH/ITO immunoelectrode.     

Microfluidic paper-based multiplex colorimetric immunodevice based on the catalytic effect of Pd/Fe3O4@C peroxidase mimetics on multiple chromogenic reactions

In this report, a non-toxic method was proposed for the simple synthesis of palladium nanoparticles (Pd)/Fe₃O₄@C peroxidase mimetics by virtue of in situ growth of Pd nanoparticles on Fe₃O₄@C magnetic nanoparticles. And a microfluidic paper-based multiplex colorimetric immunodevice (named α-sheet) was developed by site-selectively immobilizing multiple antigens owing to its intrinsic high-efficiency catalytic activity of peroxidase mimetics to multiple chromogenic reactions. The immunosensor platform was prepared by growing a layer of flower-like gold nanoparticles which could entrap the primary antibodies onto paper sensing zones, and the as-prepared Pd/Fe₃O₄@C peroxidase mimetics was used to label secondary antibodies. In the presence of 3,3′,5,5′-tetramethylbenzidine and o-phenylenediamine chromogenic substrates, Pd/Fe₃O₄@C peroxidase mimetics catalyzed chromogenic reactions and showed different colors with respective intensity. To precisely identify the intensity, a piece of black wax printed chromatographic paper with three observing windows (named β-sheet) was flatted on α-sheet. Under the optimal condition, the proposed multiplex colorimetric immunodevice displayed wide linear ranges from 0.005 to 30 ng mL⁻¹ with low detection limits of 1.7 pg mL⁻¹ for carcinoembryonic antigen (CEA) and α-fetoprotein (α-AFP). Meanwhile, the proposed method provided provided a non-toxic, low-cost and promising tool for point-of-care diagnosis.     

Magnetic solid-phase extraction of Zineb by C18-functionalised paramagnetic nanoparticles and determination by first-derivative spectrophotometry

Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles have been synthesised and used as magnetic solid-phase extraction (MSPE) sorbent for the extraction of Zineb from agricultural aqueous samples under ultrasonic condition and quantified through a first-derivative spectrophotometric method. The produced magnetic nanoparticles were characterised by using scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and zeta potential reader. The Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles had spherical structures with diameters in the range of 198–201 nm. Further, MSPE was performed by dispersion of Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles in a buffered aqueous solution accompanied by sonication. Next, the sorbents were accumulated by applying an external magnetic field and were washed with 4-(2-pyridylazo) resorcinol-dimethyl sulfoxide solution, for the purpose of desorbing the analyte. The extraction conditions (sample pH, washing and elution solutions, amount of sorbents, time of extraction, sample volume and effect of diverse ions), as well as Zineb-PAR first-order derivative spectra, were also evaluated. The calibration curve of the method was linear in the concentration range of 0.055–24.3 mg L^?1 with a correlation coefficient of 0.991. The limit of detection and limit of quantification values were 0.022 and 0.055 mg L^?1, respectively. The precision of the method for 0.27 mg L^?1 solution of the analyte was found to be less than 3.2%. The recoveries of three different concentrations (0.27, 1.37 and 13.7 mg L^?1) obtained 98.3%, 98.5% and 96.0%, respectively. The proposed Fe₃O₄-SiO₂-C₁₈ paramagnetic nanoparticles were found to have the capability of reusing for 7.0 times.     

Synthesis and application of polythiophene-coated Fe3O4 nanoparticles for preconcentration of ultra-trace levels of cadmium in different real samples followed by electrothermal atomic absorption spectrometry

In this research, magnetic Fe₃O₄ nanoparticles were synthesised by co-precipitation method and modified with polythiophene (PT) to produce Fe₃O₄-PT nanoparticles for preconcentration and determination of cadmium (??) ion followed by electrothermal atomic absorption spectrometry. The results of FT-IR spectroscopy, EDX analysis and SEM images show that Fe₃O₄-PT nanoparticles were synthesised successfully. Different parameters such as sample pH, amounts of adsorbent, sample volume, extraction time, type and concentration of eluent and desorption time were completely investigated and optimum conditions were selected.

Under the optimum conditions, the calibration curve was linear in the range of 0.01–0.25 µg L^?1 of cadmium (??). The relative standard deviation was 4.7% (n = 7, 0.10 µg L^?1 Cd²⁺) and limit of detection was 3.30 ng L^?1. The accuracy of the proposed method was verified by the analysis of a certified reference material and spike method. Finally, the proposed method was applied for the determination of ultra-trace levels of cadmium (??) in different water and food samples.     

Preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-C18 nano-magnetic composite materials and their cleanup properties for organophosphorous pesticides

Magnetic Fe₃O₄-C18 composite nanoparticles of approximately 5–10 nm in size were synthesized and characterized by IR spectroscopy, atomic absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. The magnetic Fe₃O₄-C18 composite nanoparticles were applied for cleanup and enrichment of organophosphorous pesticides. Comparative studies were carried out between magnetic Fe₃O₄-C18 composite nanoparticles and common C18 materials. Residues of organophosphorous pesticides were determined by gas chromatography in combination with a nitrogen/phosphorus detector. The cleanup and enrichment properties of magnetic Fe₃O₄-C18 composite nanoparticles are comparable with those of common C18 materials for enrichment of organophosphorous pesticides, but the cleanup and enrichment are faster and easier to perform. Figure Presumed mechanism for the adhesion of the OPs to the Fe₃O₄-C18 magnetic nanoparticles     

Electrochemical immunoassay of benzo[a]pyrene based on dual amplification strategy of electron-accelerated Fe3O4/polyaniline platform and multi-enzyme-functionalized carbon sphere label

An electrochemical immunosensor, basing on a dual amplification strategy by employing a biocompatible Fe₃O₄/polyaniline/Nafion (Fe₃O₄/PANI/Nafion) layer as sensor platform and multi-enzyme-antibody functionalized highly-carbonized spheres (multi-HRP-HCS-Ab₂) as label, was constructed for sensitive detection of benzo[a]pyrene (BaP). The stable film, Fe₃O₄/PANI/Nafion, can not only immobilize biomolecules, but also catalyze the reduction of hydrogen peroxide, indicating an accelerated electron transfer pathway of the platform. The experimental conditions, including the concentration of Nafion, concentration of Fe₃O₄/polyaniline (Fe₃O₄/PANI), pH of the detection solution and concentrations of biomolecules, were studied in detail. Basing on a competitive immunoassay, the current change was proportional to the logarithm of BaP concentration in the range of 8 pM and 2 nM with the detection limit of 4 pM. The proposed immunosensor exhibited acceptable reproducibility and stability. This new type of dual amplification strategy may provide potential applications for the detection of environmental pollutants.