Surface Polymers on Multiwalled Carbon Nanotubes for Selective Extraction and Electrochemical Determination of Rhodamine B in Food Samples

In this study, we combine magnetic solid phase extraction (MSPE), with the screen-printed carbon electrode (SPCE) modified by a molecular imprinted polymer (MIP) for sensitive and selective extraction and electrochemical determination of Rhodamine B in food samples. A magnetic solid phase extraction (MSPE) was carried out using magnetic poly(styrene-co-divinylbenzene) (PS-DVB) and magnetic nanoparticles (MNPs) synthetized on the surface of multiwalled carbon nanotubes (MWCNTs). An MIP was prepared on the surface of MWCNTs in the presence of titanium oxide nanoparticles (TiO₂NPs) modifying the SPCE for the rapid electrochemical detection of Rhodamine B. The MIPs synthesis was optimized by varying the activated titanium oxide (TiO₂) and multiwalled carbon nanotubes (MWCNTs) amounts. The MSPE and electrochemical detection conditions were optimized as well. The present method exhibited good selectivity, high sensitivity, and good reproducibility towards the determination of Rhodamine B, making it a suitable method for the determination of Rhodamine B in food samples.     

Synthesis of molecularly imprinted dye‐silica nanocomposites with high selectivity and sensitivity: Fluorescent imprinted sensor for rapid and efficient detection of τ‐fluvalinate in vodka

An imprinted fluorescent sensor was fabricated based on SiO₂ nanoparticles encapsulated with a molecularly imprinted polymer containing allyl fluorescein. High fluorine cypermethirin as template molecules, methyl methacrylate as functional monomer, and allyl fluorescein as optical materials synthesized a core‐shell fluorescent molecular imprinted sensor, which showed a high and rapid sensitivity and selectivity for the detection of τ‐fluvalinate. The sensor presented appreciable sensitivity with a limit of 13.251 nM, rapid detection that reached to equilibrium within 3 min, great linear relationship in the relevant concentration range from 0 to 150 nM, and excellent selectivity over structural analogues. In addition, the fluorescent sensor demonstrated desirable regeneration ability (eight cycling operations). The molecularly imprinted polymers ensured specificity, while the fluorescent dyes provided the stabile sensitivity. Finally, an effective application of the sensor was implemented by the detection of τ‐fluvalinate in real samples from vodka. The molecularly imprinted fluorescent sensor showed a promising potential in environmental monitoring and food safety.     

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.     

Magnetic relaxation switch and colorimetric detection of thrombin using aptamer-functionalized gold-coated iron oxide nanoparticles

We describe a sensitive biosensing system combining magnetic relaxation switch diagnosis and colorimetric detection of human α-thrombin, based on the aptamer–protein interaction induced aggregation of Fe₃O₄@Au nanoparticles. To demonstrate the concept, gold-coated iron oxide nanoparticle was synthesized by iterative reduction of HAuCl₄ onto the dextran-coated Fe₃O₄ nanoparticles. The resulting core–shell structure had a flowerlike shape with pretty narrow size distribution (referred to as “nanorose”). The two aptamers corresponding to human α-thrombin were conjugated separately to two distinct nanorose populations. Once a solution containing human α-thrombin was introduced, the nanoroses switched from a well dispersed state to an aggregated one, leading to a change in the spin–spin relaxation time (T₂) as well as the UV–Vis absorption spectra of the solution. Thus the qualitative and quantitative detection method for human α-thrombin was established. The dual-mode detection is clearly advantageous in obtaining a more reliable result; the detection range is widened as well. By using the dual-mode detection method, a detectable T₂ change is observed with 1.0 nM human α-thrombin, and the detection range is from 1.6 nM to 30.4 nM.     

Designing and fabrication of a novel gold nanocomposite structure: application in electrochemical sensing of bisphenol A

In this article, a highly sensitive electrochemical sensor is introduced for direct electro-oxidation of bisphenol A (BPA). The novel nanocomposite was prepared based on multi-walled carbon nanotube/thiol functionalised magnetic nanoparticles (Fe₃O₄-SH) as an immobilisation platform and gold nanoparticles (AuNPs) as an amplifying electrochemical signal. The chemisorbed AuNPs exhibited excellent electrochemical activity for the detection of BPA. Some analysing techniques such as Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy-dispersive x-ray diffraction exposed the formation of nanocomposite. Under optimum conditions (pH 9), the sensor showed a linear range between 0.002–240 μM, with high sensitivity (0.25 μA μM^?1) along with low detection limit (6.73 × 10^?10 M). Moreover, nanocomposites could efficiently decrease the effect of interfering agents and remarkably enhance the utility of sensor at detection of BPA in some real samples.     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Highly sensitive acetone gas sensor based on ultra-low content bimetallic PtCu modified WO3·H2O hollow sphere

Acetone is an important industrial raw material as well as biomarker in medical diagnosis. The detection of acetone has great significance for safety and health. However, high selectivity and low concentration (ppb level) detection remain challenges for semiconductor gas sensor. Herein, we present a novel sensitive material with bimetallic PtCu nanocrystal modified on WO₃·H₂O hollow spheres (HS), which shows high sensitivity, excellent selectivity, fast response/recovery speed and low limit of detection (LOD) to acetone detection. Noteworthy, the response (R_a/R_g) of WO₃·H₂O HS sensor increased by 9.5 times after modification with 0.02% bimetallic PtCu nanocrystals. The response of PtCu/WO₃·H₂O HS to 50 ppm acetone is as high as 204.9 with short response/recovery times (3.4 s/7.5 s). Finally, the gas-sensitivity mechanism was discussed based on gas sensitivity test results. This research will offer a new route for high efficient acetone detection.     

Preparation of novel bovine hemoglobin surface-imprinted polystyrene nanoparticles with magnetic susceptibility

In this research, a surface imprinting strategy has been adopted in protein imprinting. Bovine hemoglobin surface-imprinted polystyrene (PS) nanoparticles with magnetic susceptibility have been synthesized through multistage core-shell polymerization system using 3-aminophenylboronic acid (APBA) as functional and cross-linking monomers. Superparamagnetic molecularly imprinted polystyrene nanospheres with poly(APBA) thin films have been synthesized and used for the first time for protein molecular imprinting in an aqueous solution. The magnetic susceptibility is imparted through the successful encapsulation of Fe₃O₄ nanoparticles. The morphology, adsorption, and recognition properties of superparamagnetic molecularly imprinted polymers (MIPs) have been investigated using transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, and vibrating sample magnetometer. Rebinding experimental results show that poly(APBA) MIPs-coated superparamagnetic PS nanoparticles have high adsorption capacity for template protein bovine hemoglobin and comparatively low nonspecific adsorption. The imprinted superparamagnetic nanoparticles could easily reach the adsorption equilibrium and achieve magnetic separation in an external magnetic field, thus avoiding some problems of the bulk polymer.     

Iron Oxide Nanoparticles: Biosynthesis,Magnetic Behavior,Cytotoxic Effect

Iron oxide nanoparticles have attracted much attention because of their superparamagnetic properties and their potential applications in many fields such as magnetic storage devices, catalysis, sensors, superparamagnetic relaxometry (SPMR), and high-sensitivity biomolecule magnetic resonance imaging (MRI) for medical diagnosis and therapeutics. In this study, iron oxide nanoparticles (Fe₂O₃ NPs) have been synthesized using a taranjabin (camelthorn or persian manna) aqueous solution. The synthesized Fe₂O₃ NPs were identified through powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), field energy scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), vibrating-sample magnetometer (VSM) and Raman technics. The results show that the nanoparticles have a hexagonal structure with 20 to 60 nm in size. The cytotoxic effect of the synthesized nanoparticles has been tested upon application against lung cancer cell (A549) lines. It was found that there is no cytotoxic activity at lower concentrations of 200 μg/mL. The ability of the synthesized nanoparticles for lead removal in wastewaters was tested. Results show that highest concentration of adsorbent (50 mg/L) has maximum removal efficiency (96.73 %). So, synthesized Fe₂O₃ NPs can be a good candidate to use as heavy metals cleaner from contaminated waters.     

Development of superparamagnetic high-magnetization C18-functionalized magnetic silica nanoparticles as sorbents for enrichment and determination of methylprednisolone in rat plasma by high performance liquid chromatography

In this study, a novel extraction and enrichment technique based on superparamagnetic high-magnetization C₁₈-functionalized magnetic silica nanoparticles (C₁₈-MNPs) as sorbents was successfully developed for the determination of methylprednisolone (MP) in rat plasma by high performance liquid chromatography (HPLC). The synthesized silica-coated magnetite modified with chlorodimethyl-n-octadecylsilane was about 320 nm in diameter with strong magnetism and high surface area. It provided an efficient way for extraction and concentration of MP in the samples through hydrophobic interaction by the interior C₁₈ groups. Moreover, MP adsorbed with C₁₈-MNPs could be simply and rapidly isolated through placing a strong magnet on the bottom of container, and then easily eluted from C₁₈-MNPs by n-hexane solution. Extraction conditions such as amounts of C₁₈-MNPs added, adsorption time and desorption solvent, were investigated. Method validations including linear range, detection limit, precision, and recovery were also studied. The results showed that the proposed method based on C₁₈-MNPs was a simple, accurate and high efficient approach for the analysis of MP in the complex plasma samples.     

Optimization and performance evaluation of a fluorescent sensor for residual sulfonamide antibiotics in honey samples

In the quest to address the mounting concerns over sulfonamide antibiotic residues in food, which pose significant threats to public health and food safety, this study introduces a cutting-edge detection method. Surface molecular imprinting on silicon nanoparticles is harnessed to fabricate a novel fluorescent sensor that exploits the luminescent properties of cadmium telluride (CdTe) quantum dots. This innovative approach aims to detect residual sulfonamide antibiotics with high specificity and sensitivity. At the heart of this research is the development of a core-shell nanostructure, where silicon dioxide serves as the core, and a molecularly imprinted polymers (MIPs) layer, tailored to recognize sulfamethazine (SM₂), forms the shell. The pivotal advancement in this sensor design is the integration of highly fluorescent CdTe quantum dots within the MIPs layer, which significantly enhances the signal response, enabling the detection of SM₂ with remarkable precision. The synthesis of this sensor employs a novel strategy, utilizing 3-aminopropyltriethoxysilane as the functional monomer, while tetraethyl orthosilicate and ammonium hydroxide act as catalysts to facilitate the polymerization reaction. This meticulous process yields a stable core-shell structure with active fluorescent properties. Experimental results reveal that under optimal conditions, the sensor exhibits a robust linear response to SM₂ concentrations ranging from 10 to 60 μmol L⁻¹, with a detection limit as low as 0.78 μmol L⁻¹. Furthermore, when applied to real food samples, such as honey, the sensor not only demonstrates high recovery rates of 92.3%–98.1%, but also maintains a low relative standard deviation of less than 2.5%. The implications of this study are far-reaching, offering a promising avenue for the rapid and reliable monitoring of antibiotic residues in the food supply chain, thereby safeguarding consumer health and upholding food safety standards.     

Wash-free magnetic oligonucleotide probes-based NMR sensor for detecting the Hg ion

An easily applied and sensitive sensor for the detection of heavy metal ion residues based entirely on magnetic nanoparticle and oligonucleotide was developed. The tool is established on the relaxation of magnetic nanoparticles with different dispersion states. The target analyte, Hg ions, induce the aggregation of the MNP oligonucleotide probes. Accordingly, the light produced by the magnetic relaxation image and the transverse relaxation time (T(2)) all change due to the effect of the aggregation. The limit of qualitative detection of the sensor is 0.15 ppt. The recoveries from test samples range between 97.1-101.8%. Using the nuclear resonance instrument, the method is a high throughput and sensitive sensor.     

Highly sensitive electrochemical immunoassay for human IgG using double-encoded magnetic redox-active nanoparticles

A new sandwich-type electrochemical immunoassay was developed for the detection of human IgG using doubly-encoded and magnetic redox-active nanoparticles as recognition elements on the surface of a glassy carbon electrode modified with anti-IgG on nanogold particles. The recognition elements were synthesized by coating magnetic Fe₃O₄ nanoparticles with Prussian blue nanoparticles and then covered with peroxidase-labeled anti-IgG antibodies (POx-anti-IgG) on Prussian blue nanoparticles. The immunoelectrode displays very good electrochemical properties towards detection of IgG via using double-encoded magnetic redox-active nanoparticles as trace and hydrogen peroxide as enzyme substrate. Its limit of detection (10 pmol·L^?1) is 10-fold better than that of using plain POx-anti-IgG secondary antibodies. The method was applied to the detection of IgG in serum samples, and an excellent correspondence with the reference values was found.     

Microstructure and Magnetic Properties of Carbon‐Coated Nanoparticles

Abstract

In the present work, microstructure and superparamagnetic properties of two types of carbon‐coated magnetic Ni and Fe nanoparticles [Ni(C) and Fe(C)] are reviewed. High‐resolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and x‐ray diffraction (XRD) analyses have been used to reveal the distinct structural morphologies of Ni and Fe nanoparticles. Moreover, novel carbon‐coated Ni nanoparticle assemblies offer us great opportunities for studying the mechanism of superparamagnetism in particle assemblies. Magnetization measurements [M(T) and M(H) curves] for assemblies of Ni nanoparticles indicate that modified superparamagnetic properties at T > T _B, have been found in the assemblies of Ni(C) particles. The blocking temperature, T _B, is determined to be near 115K under a certain applied field. Above T _B, the magnetization M(H, T) can be described by the classical Langevin function L using the relation, M/M _s (T = 0) = coth (μH/kT) ? kT/μH. It is suggested that these assemblies of carbon‐coated Ni nanoparticles have typical single‐domain, field‐dependent superparamagnetic relaxation properties. Finally, Mössbauer spectra and hyperfine magnetic fields at room temperature for the assemblies of Fe(C) nanoparticles confirm their distinct nanophases that were detected by structural analysis. Modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles, which is attributed to the nanocrystalline nature of the carbon‐coated nanoparticles.     

Effect of the production conditions on the size and magnetic characteristics of iron sulfide Fe<Subscript>3</Subscript>S<Subscript>4</Subscript> nanoparticles

It was shown that the reaction of the trinuclear complex [FeFe₂O(CH₃CO₂)₆(H₂O)₃]·₂H₂O with thiourea in tetraethylene glycol leads to the formation of nanoparticles of thiospinel Fe₃S₄, the size of which depends on the reaction conditions. It was established that the formed thiospinel particles exhibit superparamagnetic characteristics. It was shown that the size of the nanoparticles has an effect on their magnetic characteristics.     

Application of zein‐modified magnetite nanoparticles in dispersive magnetic micro‐solid‐phase extraction of synthetic food dyes in foodstuffs

A simple method for the simultaneous and trace analysis of four synthetic food azo dyes including carmoisine, ponceau 4R, sunset yellow, and allura red from some foodstuff samples was developed by combining dispersive μ‐solid‐phase extraction and high‐performance liquid chromatography with diode array detection. Zein‐modified magnetic Fe₃O₄ nanoparticles were prepared and used for μ‐solid‐phase extraction of trace amounts of mentioned food dyes. The prepared modified magnetic nanoparticles were characterized by scanning electron microscopy and FTIR spectroscopy. The factors affecting the extraction of the target analytes such as pH, amount of sorbent, extraction time, type and volume of the desorption eluent, and desorption time were investigated. Under the optimized conditions, the method provided good repeatability with relative standard deviations lower than 5.8% (n = 9). Limit of detection values ranged between 0.3 and 0.9 ng/mL with relatively high enrichment factors (224–441). Comparing the obtained results indicated that Fe₃O₄ nanoparticles modified by zein biopolymer show better analytical application than bare magnetic nanoparticles. The proposed method was also applied for the determination of target synthetic food dyes in foodstuff samples such as carbonated beverage, snack, and candy samples.     

Aptamer-quantum dots and teicoplanin-gold nanoparticles constructed FRET sensor for sensitive detection of Staphylococcus aureus

The detection of bacterial pathogen such as Staphylococcus aureus(S.aureus) is essential for the regulation of food hygiene and disease diagnosis.Herein,we developed a simple one-step fluorescence resonance energy transfer(FRET)-based sensor for specific and sensitive detection of S.aureus in food and serum samples,in which aptamer-modified quantum dots(aptamer-QDs) was employed as the energy donor and antibiotic of teicoplanin functionalized-gold nanoparticles(Teico-AuNPs) was chosen as the energy acceptor.Within 1 h,the FRET-based sensor showed a linear range of from 10 cfu/mL to 5 × 10~8 cfu/mL,with the low limit of detection(LOD,2 cfu/mL) for S.aureus in buffer.When further applied to assay S.aureus in real samples,the FRET-based sensor showed good recoveries ranging from 84.5% to 110.0%,with relative standard derivations(RSDs) of 0.01%-0.44% and a LOD of 100 cfu/mL in milk,orange juice and human serum.     

Pathogen detection in complex samples by quartz crystal microbalance sensor coupled to aptamer functionalized core–shell type magnetic separation

A quartz crystal microbalance sensor (QCM) was developed for sensitive and specific detection of Salmonella enterica serovar typhimurium cells in food samples by integrating a magnetic bead purification system. Although many sensor formats based on bioaffinity agents have been developed for sensitive and specific detection of bacterial cells, the development of robust sensor applications for food samples remained a challenging issue. A viable strategy would be to integrate QCM to a pre-purification system. Here, we report a novel and sensitive high throughput strategy which combines an aptamer-based magnetic separation system for rapid enrichment of target pathogens and a QCM analysis for specific and real-time monitoring. As a proof-of-concept study, the integration of Salmonella binding aptamer immobilized magnetic beads to the aptamer-based QCM system was reported in order to develop a method for selective detection of Salmonella. Since our magnetic separation system can efficiently capture cells in a relatively short processing time (less than 10 min), feeding captured bacteria to a QCM flow cell system showed specific detection of Salmonella cells at 100 CFU mL⁻¹ from model food sample (i.e., milk). Subsequent treatment of the QCM crystal surface with NaOH solution regenerated the aptamer-sensor allowing each crystal to be used several times.     

Magnetic force-based multiplexed immunoassay using superparamagnetic nanoparticles in microfluidic channel

This paper describes a novel microfluidic immunoassay utilizing binding of superparamagnetic nanoparticles to beads and deflection of these beads in a magnetic field as the signal for measuring the presence of analyte. The superparamagnetic 50 nm nanoparticles and fluorescent 1 microm polystyrene beads are immobilized with specific antibodies. When target analytes react with the polystyrene beads and superparamagnetic nanoparticles simultaneously, the superparamagnetic nanoparticles can be attached onto the microbeads by the antigen-antibody complex. In the poly(dimethylsiloxane)(PDMS) microfluidic channel, only the microbeads conjugated with superparamagnetic nanoparticles by analytes consequently move to the high gradient magnetic fields under the specific applied magnetic field. In this study, the magnetic force-based microfluidic immunoassay is successfully applied to detect the rabbit IgG and mouse IgG as model analytes. The lowest concentration of rabbit IgG and mouse IgG measured over the background is 244 pg mL(-1) and 15.6 ng mL(-1), respectively. The velocities of microbeads conjugated with superparamagnetic nanoparticles are demonstrated by magnetic field gradients in microfluidic channels and compared with the calculated magnetic field gradients. Moreover, dual analyte detection in a single reaction is also performed by the fluorescent encoded microbeads in the microfluidic device. Detection range and lower detection limit can be controlled by the microbeads concentration and the higher magnetic field gradient.     

Multi-reservoir device for detecting a soluble cancer biomarker

By combining the sensing capabilities of nanoscale magnetic relaxation switches (MRS) within multi-reservoir structures, a potentially powerful implantable multiplexed sensor has been developed. MRS are magnetic nanoparticles that decrease the transverse relaxation time (T(2)) of water in the presence of an analyte. The switches encased in polydimethylsiloxane (PDMS) devices with polycarbonate membranes (10 nm pores) have demonstrated in vitro sensing of the beta subunit of human chorionic gonadotrophin (hCG-beta), which is elevated in testicular and ovarian cancer. Devices showed transverse relaxation time (T(2)) shortening by magnetic resonance imaging (MRI) when incubated in analyte solutions of 0.5 to 5 microg hCG-beta mL(-1). The decrease in T(2) was between 9% and 27% (compared to control devices) after approximately 28 h. This prototype device is an important first step in developing an implantable sensor for detecting soluble cancer biomarkers in vivo.