Surface Of Magnetic Particles Research Articles

The development and evaluation of chitosan-coated enzyme magnetic nanoparticles for cellulose hydrolysis

The recycling capability, colloidal and thermal stability of exo-cellulase, endo-cellulase, and β-glucosidases with magnetic particles (MNPs) were evaluated. Co-precipitation and oxidation of Fe(OH)2 methods were used to fabricate magnetic nanoparticles. Three different enzymes were covalently bound to the surface of MNPs using 3-(aminopropyl) triethoxysilane (APTES) and a common protein crosslinking agent, glutaraldehyde. To evaluate the increase in colloidal dispersion stability, chitosan-coating was applied on MNPs and evaluated through particle settlement tests. The results showed that the chitosan-coated MNPs had 3.7 times higher colloidal dispersion stability than the bare MNPs. X-ray photoelectron spectroscopy (XPS) confirmed each magnetic nanoparticle surface modification step and successful enzyme binding. The optimum bioconjugate ratio in exo-cellulase, endo-cellulase, and β-glucosidases was evaluated, and having a high endo-cellulase bioconjugate in the reaction produced the highest glucose. The bioconjugates showed superior glucose productivity 39.4% at 65°C and 22.2% at 88°C in which the native enzyme is inactivated completely after 5 h of exposure. Recycling stability studies showed approximately 78% of activity was retained after 10 cycles and 32% of activity was retained after 20 cycles. The bioconjugates demonstrated equivalent total product conversions as a single reaction of an equivalent amount of the native enzyme after the 10th cycle this work introduces a novel method for covalently binding individual exo-cellulase, endo-cellulase, and β-glucosidases. These bioconjugates showed superior thermal stability and recyclability. It was also demonstrated that chitosan coating significantly improves the colloidal dispersion stability of bioconjugates. Thus this work validates the use of enzyme-MNP bioconjugates to effectively glucose production and promising technique for eventual continuous biological processes.

Self-assembled magnetic particles on hard magnetic materials substrate for simple and rapid SERS detection of organic dye

In this paper, a detection strategy based on Surface-enhanced Raman Scattering (SERS) was proposed to quickly and simply separate target molecules from samples. Fe3O4@SiO2@Ag (FSA) magnetic particles modified with flower-like silver nanosheets were employed for efficient enrichment of target molecules, followed by their self-assembly onto the NdFeB substrate surface in fluid medium. The SERS sensitivity was indirectly adjusted by changing the reaction time to control the morphology of flower-like silver nanosheets on the surface of magnetic particles. SERS experiment showed that the substrate prepared by this detection strategy had high sensitivity, Rhodamine 6G (R6G) could be detected at the concentration of 10−8M and Methylene Blue (MB) could be detected at the concentration of 10−7M, the calculated enhancement factor was 1.34 × 105. In addition, the uniformity of the substrate was evaluated by SERS mapping using 10-6 M R6G, the RSD value of 8.89% was obtained. This detection strategy provides a new idea for simple and rapid SERS detection of organic dye.

Differences in the magnetic properties of Finemet/FeSi soft magnetic composites prepared with epoxy resin/nano-oxide composite coating layers

Organic and inorganic composite coating layers have attracted significant attention because of their excellent insulating properties. In this study, nano-oxide/epoxy resin composite coating layers were prepared in FeSiBCuNb/FeSi soft magnetic composites (SMCs). And the influence of Al2O3, CeO2, SiO2 and Fe3O4 nano-oxides on the properties of SMCs is analyzed in detail. The density and phase structure of nano-oxides result in differences in their modifiable and agglomerative properties, affecting the insulation coating layers on the surface of magnetic particles. This is refilected as a change in magnetic properties on a macroscopic scale. Analysis results show that the introduction of nano-Al2O3 significantly decreases the effective permeability of SMCs. However, it exhibits excellent loss characteristics in the high-frequency field of 5 MHz. The introduction of nano-CeO2 optimizes the losses and effective permeability of SMCs at 1 MHz. And the losses and effective permeability of SMCs are 591.4 mW/cm3 (20mT, 1 MHz) and 35.5 (1 MHz), respectively. This work provides a reference for selecting nano-oxides in the insulation coating layers of SMCs.

A chemical-free magnetophoretic approach for recovering magnetic particles in microalgae removal through magnetic separation

Magnetic separation can swiftly remove many substances (e.g., biomolecules, cells, and viruses) from water. In algal bloom mitigation and biomass dehydration, magnetic particles (MPs) with proper surface modifications could effectively attract and remove algae from the impaired water body. It has long been expected to recover and reuse magnetic nanoparticles or particles to reduce the algal removal cost and potential adverse effects on the environment. This study evaluated the use of a tunable magnetic field to remove algae using functionalized MPs coated with polymers: polyethyleneimine (PEI), chitosan (CTS), and cetyltrimethyl ammonium bromide (CTAB), whose recovery and reuse were examined. The results show that PEI-coated MPs and CTS-coated MPs at the coating density of 2.3 g-cationic polymers·g-MPs−1 achieved higher removal efficiencies of 88.61 ± 9.12% and 73.19 ± 0.37%, respectively, toward a model algal cell (i.e., Scenedesmus obliquus) within a 5-min separation time. In contrast, CTAB-coated MPs and pristine MPs exhibited lower removal efficiencies (47.46 ± 0.3% and 52.69 ± 0.44%, respectively). Furthermore, the removal efficiency of PEI-coated MPs was further improved to over 95% under pH 7, the highest magnetic field of 40 mT, and algogenic organic matter-free conditions. Adsorption kinetics and isotherm analysis revealed that chemical and physical interactions drive the adsorption of a monolayer of algal cells on the surface of magnetic particles. Atomic force microscopy and quartz crystal microbalance confirmed a strong adhesion force and rate between functionalized MPs and algae, which affect both algal removal efficiency and MPs recovery from algae-MPs aggregates. The extended Derjaguin−Landau−Verwey−Overbeek (EDLVO) theory predicted a strong attractive force between algae and cationic polymer-coated MPs, which supported the enhanced algal removal. Finally, almost 99% of the four MPs could be recovered from separated algae-MPs aggregates within 30 s under the strong magnetic field and exhibited excellent magnetic responsiveness and reusability in further separation cycles. This study establishes a foundation for coagulant-free algae removal and enables the potential sustainable separation processes.

A novel Fe3O4@Pt synthetized via a self-assembly strategy as efficient Fenton-like@mimetic enzyme catalyst for degradation of tetracyclines in food processing wastewater

The self-assembly approach has successfully been used to generate Fe3O4@Pt, a material that can mimic peroxidase. The material was created by modifying the surface of Fe3O4 nanoparticles (Fe3O4 NPs) with -NH2 functional groups using 3-Aminopropyltriethoxysilane (APTES), and then using the coordination between platinum ions and -NH2 on the surface of magnetic particles to reduce platinum ions to the surface of magnetic particles under ultrasonic conditions to produce Fe3O4@Pt composite nanoparticles. The Fe3O4@Pt core-shell composite material not only has the inert metal Pt to protect Fe3O4 to improve the stability of Fe3O4 in the biological matrix, but also has the high catalytic activity of Fe3O4 and Pt. The catalysts were characterized, and the findings revealed that they were non-homogeneous Fenton catalysts with high dispersion, uniform particle size, and a large specific surface area. Since a large number of free radicals generated during the catalysis of Fe3O4@Pt mimic enzyme can trigger the Fenton reaction, tetracycline (TC) and oxytetracycline (OTC) were chosen as target substances, and a system for the combined degradation of tetracyclines pollutants by mimic enzyme and Fenton reaction was established, and the catalytic mechanism of this system has been investigated. The findings indicate that by using a concentration of 0.25 mol/L of H2O2, a catalyst amount of 1.5 g/L, a reaction time of 50 min, and a reaction temperature of 50°C, the degradation rate of TC and OTC can exceed 97 %, following first-order degradation kinetics. Under ideal conditions, over 95 % of each tetracyclines was degraded in the simulated food processing wastewater, effectively achieving tetracyclines degradation in the actual wastewater. In addition, the reusability of the recovered Fe3O4@Pt mimetic enzyme was investigated. The findings indicated that the Fe3O4@Pt mimetic enzyme has exceptional activity, stability, and reproducibility. The combination of the Fenton reaction with the Fe3O4@Pt mimetic enzyme can expedite the degradation of tetracyclines, offering a novel approach for eliminating recalcitrant contaminants in wastewater.

Fluorescent Composite Nano‐ and Microparticles Based on Xanthene Dyes and Iron Oxides

AbstractModern industry actively uses metal structural materials to create innovative devices and components. In order to prevent emergency situations in production, nondestructive testing methods are used to detect defects on the surface of the material being developed. Among the methods of nondestructive testing, one can highlight the method of luminescent magnetic flaw detection, which allows identifying defects on the surface and under the surface of the test sample with minimal effort. It is known that in some cases, the magnetic‐powder method cannot achieve the required sensitivity due to the shape and location of defects themselves or due to certain conditions of object operation. To increase the visibility and sensitivity, magnetic nano‐ and microparticles can be conjugated with the dyes. Iron oxide nanoparticles (Fe3O4, γ‐Fe2O3) can be used as such magnetic particles, since they are quite easy to obtain and have low toxicity, high chemical stability, and a wide variety of magnetic properties. To ensure fluorescence of magnetic particles, a wide variety of fluorescent dyes associated with such particles are used. The dyes can include morin, naphthalimide derivatives, as well as semiconductor quantum dots. This article provides a review of fluorescent composite micro‐ and nanoparticles based on xanthene dyes (rhodamine, fluorescein, and pyronine). Such dyes are economically available luminophores, have good binding to the surface of magnetic particles, and therefore can be suitable for luminescent magnetic flaw detection. This review article discusses methods for producing composite nano‐ and microparticles of iron oxides with xanthene dyes and provides prospects of using composite nano‐ and microparticles in nondestructive testing methods.

(Deep eutectic solvent-ionic liquid)-based ferrofluid a new class of magnetic colloids for determination of tamoxifen and its metabolites in human plasma samples

In this research, a novel category of magnetic colloid was created by immobilizing an ionic liquid on the surface of silica-coated magnetic particles. This was followed by utilizing a natural hydrophobic deep eutectic solvent as a carrier. This magnetic colloid served as an adsorbent in dispersive solid-phase microextraction, combined with liquid chromatography-UV detection, for analyzing tamoxifen and its three active metabolites in plasma samples. After optimizing the effective variables in the analysis, the method underwent validation. Linearity was observed in the calibration model between 0.2 and 5.0 µg/L. The range of the detection limit was found to be 0.2–200.0 µg/L. Assessing the method's precision involved evaluating the intra- and inter-day precision at three analyte concentrations, which determined less than 7.5 % and 11.2 %, respectively. Moreover, the accuracy fell between 94.3 % and 105.1 %. The method's feasibility was evaluated using human plasma samples that ranged in concentrations of tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen, and endoxifen, respectively, from 28.3 to 39.7, 25.9–42.7, ≈1.3, and 3.4–7.2 μg L-1. Among the many benefits of this approach is the removal of the requirement for additional electronic accessories and dispersive solvents. It also minimizes the sample size, making it easily automatable. The method's applicability was demonstrated using human plasma samples, which provided quantification ranges for various tamoxifen metabolites. This technique has a lot of potential for studying the pharmacodynamics, therapeutic drug monitoring, andpharmaceutical kineticsof tamoxifen and its metabolites in bodily fluids, which will help with clinical research and drug analysis.

Polycarboxylate functionalized magnetic nanoparticles Fe3O4@SiO2@CS-COOH: Preparation, characterization, and immobilization of bovine serum albumin

Magnetic nanoparticles with increasing superparamagnetism and magnetic targeting have found widespread application in fields such as food and medicine. In this study, polycarboxylated magnetic nanoparticles (Fe3O4@SiO2@CS-COOH) were prepared by surface functionalizing iron tetraoxide (Fe3O4) nanoparticles with ethylenediaminetetraacetic acid (EDTA) as a modifier. The appropriate degree of functionalization modification was obtained by adjusting the EDTA concentration and the ratio of cross-linking agents. The prepared magnetic nanoparticles were analyzed with structural and property characterization. The results showed that the Fe3O4@SiO2@CS-COOH magnetic nanoparticles prepared with 4 % EDTA and cross-linking agents at a molar ratio of 3:4 were uniform in particle size, with an average size of roughly 7 nm, and possessed an abundant carboxylate content (310.8064 μmol/g) and a high magnetization intensity (35.05 emu/g). As a model protein, bovine serum albumin (BSA) was immobilized on the surface of magnetic particles. The largest amount of immobilized protein was 500.4376 mg BSA/g at pH 4.0 and no extra salt ions. According to molecular docking simulations, its immobilization was due to the interaction of amino and carboxyl groups at the Fe3O4@SiO2@CS-COOH/BSA interface. Fe3O4@SiO2@CS-COOH possesses a large number of carboxyl groups, strong protein immobilization, and magnetic responsiveness, which may have potential applications in biomedical and food fields.

Fe3O4@Co3S4 Nanocatalyst: Enhanced Activation of Peroxymonosulfate for Acetaminophen Degradation

How to accelerate the electron transfer to promote the circulating efficiency of Fe[Formula: see text]/Fe[Formula: see text] is a key problem to be solved, so that magnetic particles can activate peroxymonosulfate well to efficiently degrade acetaminophen (ACE). Herein, a Fe3O4@Co3S4 catalyst was prepared by modifying Co3S4 nanosheets on the surface of magnetic Fe3O4 particles. The Co[Formula: see text] in the modified layer Co3S4 accelerates the rate of electron transfer between Fe[Formula: see text] and Fe[Formula: see text], thus promoting the circulating efficiency of Fe[Formula: see text]/Fe[Formula: see text]. Fe3O4@Co3S4/PMS system can degrade over 95% of ACE within 5[Formula: see text]min. Quenching experiment and ESR tests prove that non-radical 1O2 and [Formula: see text] played predominant roles in the advanced oxidation process. And after six cycles, the degradation rate could still be higher than 50%.

Ready-to-use nanopore platform for label-free small molecule quantification: Ethanolamine as first example

In recent decades, nanopores have become a promising diagnostic tool. Protein and solid-state nanopores are increasingly used for both RNA/DNA sequencing and small molecule detection. The latter is of great importance, as their detection is difficult or expensive using available methods such as HPLC or LC-MS. DNA aptamers are an excellent detection element for sensitive and specific detection of small molecules. Herein, a method for quantifying small molecules using a ready-to-use sequencing platform is described.Taking ethanolamine as an example, a strand displacement assay is developed in which the target-binding aptamer is displaced from the surface of magnetic particles by ethanolamine. Non-displaced aptamer and thus the ethanolamine concentration are detected by the nanopore system and can be quantified in the micromolar range using our in-house developed analysis software. This method is thus the first to describe a label-free approach for the detection of small molecules in a protein nanopore system.

A novel coarse-grained modeling and simulation for the microstructure evolution of ferrofluids

Ferrofluid (FF) has attracted more and more attention due to its tunable rheological properties, in which the microstructure under a magnetic field plays an important role in these properties. In this study, an innovative coarse-grained (CG) model of FF is presented for the first time to capture the microstructure evolution of FF at the nanoscale. The potential functions of carrier liquid for FF CG models are obtained by the iterative Boltzmann inversion method, and the CG nonbonded interaction between the magnetic particles (MPs) is obtained via the strain energy conservation. Then, CG molecular dynamics (CGMD) simulations are used to study the microstructure evolutions of FF under different magnetic fields. Notably, we demonstrate the existence of a carrier liquid adsorption layer on the MPs surface, and its thickness is calculated. The staggered arrangement style of MPs in the chains is also revealed by the CGMD method. The present FF CG model has fully considered the carrier liquid molecular structure and interaction with the MPs, and the CGMD is used to solve the problem that classical molecular dynamics cannot simulate the microstructure of FF, making the simulation results more in line with the actual situation.

Synthesis of magnetic carbon composite by diesel engine and its application to dye removal

We report a one-step and efficient method to synthesize magnetic diesel particles (MDPs) and their application toward dye removal. The MDPs were obtained by the combustion of ferrocene-doped diesel fuel using an internal combustion engine. The diesel particles combined with ferrocene as a metal source were collected by an electrostatic precipitator. The thermogravimetric analysis confirmed the ferrocene-based catalyst and thermal stability of MDPs. FE-SEM showed irregular and aggregated morphologies, and the presence of iron oxide phases (Fe4O3 and γ-Fe2O3) was confirmed by X-ray diffraction analysis. The characteristics of MDPs as an adsorbent for organic pollutants were evaluated by methylene blue (MB) adsorption experiments. Langmuir isotherm and pseudo-second-order models best interpret the adsorption process and kinetics, respectively, with a maximum adsorption capacity of 40.81 mg/g of MB adsorbed on the surface of magnetic diesel particles.

Performance of microenvironment-induced lipase immobilization on diversify surface of magnetic particle

The orientation of the enzyme molecular on the interface of the carrier affects its activity. Therefore, it is very important to controllably induce the orientation of the enzyme on the surface to improve the performance of the immobilized enzyme. Magnetic nanoparticles were used to construct microenvironments with the different surface hydrophobicity and charge characteristics by controlled modification, and those particles with various microenvironments were further used to study their interaction with the lipase. The amount and activity of immobilized enzyme on different magnetic nanoparticles surfaces were studied by physical adsorption and covalent binding. Through the enzyme surface and particle surface characteristics analysis, the possible preferred orientation of enzyme and enzyme conformation on different surfaces were inferred, which well explained the effect of surface induction on enzyme loading and activity. The methods of surface microenvironment regulation and the strategy of controllable induction of enzyme orientation adopted in this study are enlightening for the rational design of immobilized enzyme methods.

Engineering of DNA Structures Attached to Magnetic Particles for Effective Trans- and Cis-Cleavage in Cas12-Based Biosensors

Sequence-specific endonuclease Cas12-based biosensors have rapidly evolved as a strong tool to detect nucleic acids. Magnetic particles (MPs) with attached DNA structures could be used as a universal platform to manipulate the DNA-cleavage activity of Cas12. Here, we propose nanostructures of trans- and cis-DNA targets immobilized on the MPs. The main advantage of the nanostructures is a rigid double-stranded DNA adaptor that distances the cleavage site from the MP surface to ensure maximum Cas12 activity. Adaptors with different lengths were compared by detecting the cleavage by fluorescence and gel electrophoresis of the released DNA fragments. The length-dependent effects for cleavage on the MPs' surface were found both for cis- and trans-targets. For trans-DNA targets with a cleavable 15-dT tail, the results showed that the optimal range of the adaptor length was 120-300 bp. For cis-targets, we varied the length and location of the adaptor (at the PAM or spacer ends) to estimate the effect of the MP's surface on the PAM-recognition process or R-loop formation. The sequential arrangement of an adaptor, PAM, and a spacer was preferred and required the minimum adaptor length of 3 bp. Thus, with cis-cleavage, the cleavage site can be located closer to the surface of the MPs than with trans-cleavage. The findings provide solutions for efficient Cas12-based biosensors using surface-attached DNA structures.

Robust superhydrophobic magnetic melamine sponge inspired by lotus leaf surface for efficient continuous oil–water separation

Inspired by the oily surface layer and hierarchical structure on the lotus leaf surface, a magnetic sponge with robust superhydrophobicity (water contact angle up to 155°) and surface protection was synthesized by one-pot solvothermal method by introducing (3-Mercaptopropyl)trimethoxysilane into the melamine sponge. After hydrolysis and self-polymerization, (3-Mercaptopropyl)trimethoxysilane can grow as a low surface energy polysiloxane coating on the surface of sponges and magnetic particles. It not only provides a hydrophobic surface layer for sponges, but also this cooperation of micro-submicron-nanostructure from micron sponge skeleton, submicron Fe3O4 particles and nanoscale polysiloxane builds rough surfaces at multiple scales. Based on the triadic Koch curve model, the theory of superhydrophobic surface is elucidated in detail from the surface fractal behavior, fractal dimension, and surface composition. The sponge can be integrated into a negative pressure system as a filter element for continuous and efficient oil–water separation. The formed polysiloxane can not only provide protection for the sponge skeleton and magnetic particles, but also provide strong cross-linking between the two materials, which can effectively resist the damage to the functional structure caused by oil erosion. In addition, a conceptual diagram of a portable oil suction device similar to a vacuum cleaner was proposed. Combining the basic theory of robust superhydrophobic surface and innovatively clarifying the influence of filter element structure on oil–water separation efficiency from the perspective of interface force, it is expected to bring more practical and potential ideas for the design of a portable vacuum cleaner-like oil–water separation device.

Determination of testosterone in serum by magnetic molecularly imprinted polymer-coupled nano-ESI-MS

Monitoring clinical biomarkers, such as testosterone in serum, is important for disease assessment. Due to the very low concentration of testosterone in serum, we have developed a new strategy for its enrichment in serum samples by magnetic molecularly imprinted polymers (MMIPs) technology and detection by nano-electrospray ionization mass spectrometry (Nano-ESI-MS). Testosterone was selectively extracted and enriched by the imprinted polymers on the surface of magnetic particles and the complex matrix was eliminated from the serum. The linear calibration curve was in the range of 0.1–10 μg/L and the limit of detection was 11.4 ng/L. The recovery and repeatability of the spiked serum were satisfactory. These results demonstrate that the proposed method is a promising approach for quantitative analysis of testosterone in serum.

Fast exhaustive enrichment and electrochemical quantitative detection of anthocyanins from natural products by using dual responsive and dummy molecularly imprinted polymers

In this work, a new adsorbent was synthesized using dummy-template molecular imprinting technology, magnetic separation technology and pH-responsive technology, which was used to quickly enrich anthocyanins in fruit and detect with electrochemical methods. On the surface of magnetic particles, the molecularly-imprinted materials were synthesized by using quercetin as the dummy-template, 4-vinyl phenylboronic acid and methacrylic acid as the functional monomers. The microstructure was characterized by scanning electron microscopy, transmission electron microscope, Fourier transform infrared spectroscopy, N2 adsorption–desorption, thermal gravimetric analysis, vibrating sample magnetometer and X-ray photoelectron spectroscopy. Compared with structural analogue, dummy-template magnetic and pH-responsive molecularly imprinted polymers (DMMIPs) had shorter kinetic equilibrium time, higher selectivity and better adsorption capacity toward anthocyanins. The binding capacity and imprinting factor of the dummy molecularly imprinted polymer could reach 59.22 mg/g and 1.56, respectively. The anthocyanins’ content of blueberry and grape peel crude extracts were consistent with the reference reports.

Simultaneous determination of 76 pesticide residues in the traditional Chinese medicine by magnetic hydrophilic-lipophilic-balanced materials assisted matrix solid phase dispersion extraction-high performance liquid chromatography-tandem mass spectrometry

建立灵敏、可靠的中药材中农药多残留的检测方法对保证中药材的质量和安全十分重要。制备了磁性亲水亲脂平衡萃取材料Fe3O4@PLS,将其应用于农药多残留的磁性基质固相分散萃取中,并结合高效液相色谱-串联质谱法(HPLC-MS/MS)检测了金银花、菊花和三七块根(干)3种中药材中76种农药残留量。研究通过扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)和X-射线衍射仪(XRD)对磁性萃取材料Fe3O4@PLS进行表面形貌和结构的表征。同时考察了影响磁性基质固相分散萃取效率的主要因素,结果表明,磁性萃取材料Fe3O4@PLS的用量为10 mg、研磨分散吸附时间为5 min、淋洗液为10 mL 20%(v/v)甲醇水溶液、涡旋振荡清洗1 min、以0.5 mL 0.1%(v/v)甲酸乙腈为洗脱剂、涡旋振荡洗脱1 min, 76种农药的萃取效果最佳。在实际应用中,76种农药在金银花、菊花、三七块根(干)3种中药材中的萃取回收率别为69.1%~112.2%、67.1%~102.8%和70.1%~105.1%,相对标准偏差分别为2.0%~12.4%、2.1%~13.2%和2.0%~13.5%。该方法利用Fe3O4@PLS良好的磁响应性和亲水亲脂通用吸附特性,可以同时萃取极性农药(如多菌灵等)和非极性农药(如敌瘟磷等),建立了测定中药材中76种农药残留的磁性基质固相分散萃取-高效液相色谱-串联质谱联用的分析方法,具有低消耗、操作简便、灵敏度高等优点,适用于非液态中药材基质中多种类农药残留的检测。

Ultrasensitive lateral flow immunoassay of phycotoxin microcystin-LR in seafood based on magnetic particles and peroxidase signal amplification

In this study, an immunochromatographic test system for the ultrasensitive and rapid detection of the highly toxic phycotoxin microcystin-leucine-arginine (MC-LR) has been developed. The lateral flow immunoassay (LFIA) is based on an indirect competitive format with the use of magnetic particles (MPs) as a colored label for secondary antibodies and a carrier for horseradish peroxidase (HRP) as a means of signal amplification. A simple method of simultaneous covalent binding of antibodies and HRP to the surface of MPs was applied. The developed test system allows for the detection of MC-LR with an instrumental detection limit of 2 pg/mL and cutoff of 50 pg/mL within 17 min. A high specificity of the LFIA has been demonstrated: the cross-reactivity with MC-LR structural analogs was negligible. A technique for sample preparation of various seafood samples was proposed. The applicability of the LFIA for the control of MC-LR contamination of shrimp, octopus, squid, and mussels has been confirmed. The assay recoveries ranged from 71% to 115%. The developed approach is of great potential as a universal tool that can be applied to a wide range of analytes.

Surface coating preparation of spherical magnetic materials

Magnetic materials are being increasingly used in anti-counterfeiting coatings, but the dark colors of magnetic materials greatly limit their applications. This necessitates the development of light-colored magnetic materials. In this study, the heterogeneous precipitation method was used to deposit a layer of titanium dioxide (TiO2) on the surface of magnetic spherical metal particles, followed by the deposition of a layer of Ag by the reduction method, in order to achieve a light color. In the experiment, the particles were initially coated with a few tens of nanometers of TiO2 with a strong shading effect, followed by a further coating of Ag of the same thickness with a similar shading performance. Not only did this achieve a lighter color, but there was no reduction in the magnetic properties of the material after the application of the coating. Scanning electron microscopy (SEM), scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), and other methods were used to study the changes in morphology and composition before and after the magnetic material was coated. A magnetic tester was used to study the changes in magnetic strength before and after the magnetic material was coated.