A class-specific enzyme-linked immunosorbent assay based on magnetic particles for multiresidue organophosphorus pesticides

Design of an Antigen-Triggered Nanobody-Based Fluorescence Probe for PET Immunoassay to Detect Quinalphos in Food Samples

Photoinduced electron-transfer (PET) immunoassay based on a fluorescence site-specifically labeled nanobody, also called mini Quenchbody (Q-body), exhibits extraordinary sensitivity and saves much time in the homogeneous noncompetitive mode and is therefore regarded as a valuable method. However, limited by the efficiency of both quenching and dequenching of the fluorescence signal before and after antigen binding associated with the PET principle, not all original nanobodies can be used as candidates for mini Q-bodies. Herein, with the anti-quinalphos nanobody 11A (Nb-11A) as the model, we, for the first time, adopt a strategy by combining X-ray structural analysis with site-directed mutagenesis to design and produce a mutant Nb-R29W, and then successfully generate a mini Q-body by labeling with ATTO520 fluorescein. Based on this, a novel PET immunoassay is established, which exhibits a limit of detection of 0.007 μg/mL with a detection time of only 15 min, 25-fold improved sensitivity, and faster by 5-fold compared to the competitive immunoassay. Meanwhile, the recovery test of vegetable samples and validation by the standard ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) both demonstrated that the established PET immunoassay is a novel, sensitive, and accurate detection method for quinalphos. Ultimately, the findings of this work will provide valuable insights into the development of triggered PET fluorescence probes by using existing antibody resources.

Development of Magnetic Lateral Flow and Direct Competitive Immunoassays for Sensitive and Specific Detection of Halosulfuron-Methyl Using a Novel Hapten and Monoclonal Antibody

Halosulfuron-methyl (HM) is widely used for the removal of noxious weeds in corn, sugarcane, wheat, rice, and tomato fields. Despite its high efficiency and low toxicity, drift to nontarget crops and leaching of its metabolites to groundwater pose potential risks. Considering the instability of HM, the pyrazole sulfonamide of HM was used to generate a hapten and antigen to raise a high-quality monoclonal antibody (Mab, designated 1A91H11) against HM. A direct competitive immunoassay (dcELISA) using Mab 1A91H11 achieved a half-maximal inhibitory concentration (IC50) of 1.5 × 10^-3 mg/kg and a linear range of 0.7 × 10^-3 mg/kg-10.7 × 10^-3 mg/kg, which was 10 times more sensitive than a comparable indirect competitive ELISA (icELISA) and more simple to operate. A spiking recovery experiment performed in tomato and maize matrices with 0.01, 0.05, and 0.1 mg/kg HM had average recoveries within 78.9-87.9% and 103.0-107.4% and coefficients of variation from 1.1-6.8% and 2.7-6.4% in tomato and maize, respectively. In addition, a magnetic lateral flow immunoassay (MLFIA) was developed for quantitative detection of low concentrations of HM in paddy water. Compared with dcELISA, the MLFIA exhibited 3.3- to 50-fold higher sensitivity (IC50 0.21 × 10^-3 mg/kg). The average recovery and RSD of the developed MLFIA ranged from 81.5 to 92.5% and 5.4 to 9.7%. The results of this study demonstrated that the developed dcELISA and MLFIA are suitable for rapid detection of HM residues in tomato and maize matrices and paddy water, respectively, with acceptable accuracy and precision.

Novel colorimetric aptasensor based on MOF-derived materials and its applications for organophosphorus pesticides determination

For the visual detection of four organophosphorus pesticides (OPs), a colorimetric aptasensor was developed based on aptamer-mediated bimetallic metal-organic frameworks (MOFs) nano-polymers. Fe-Co magnetic nanoparticles (MNPs) and Fe-N-C nanozymes were prepared based on pyrolytic reaction, and were labeled with broad spectrum aptamers and complementary chains of organophosphorus pesticides respectively. The hybridization of aptamers and complementary chains led to the formation of nano-polymers. In the presence of target pesticides, they competed with complementary chains for aptamers on Fe-Co MNPs, resulting in a large number of Fe-N-C nanozymes signal labels being released into the supernatant. Fe-N-C nanozymes showed similar activity to peroxidase and catalyzed the 3,3',5,5'-tetramethylbenzidine-hydrogen peroxide (TMB-H₂O₂) color system to turn the solution blue-green under mild conditions. The magnetic probes had good selectivity and sensitivity, and were easily separated by magnetic absorption. The sensor functioned well under optimal conditions, demonstrating good stability and specificity for four pesticides: phorate, profenofos, isocarbophos and omethoate, and the detection limits of four pesticides were as low as 0.16 ng/mL, 0.16 ng/mL, 0.03 ng/mL and 1.6 ng/mL respectively, and the recovery rate of OPs residue in vegetable samples was satisfactory. The work described here provided a simple, rapid and sensitive way to construct a biosensor.

Magnetic layered double hydroxide nanosheet as a biomolecular vessel for enzyme immobilization

Magnetic nanoparticle coated with manganese‑aluminum layered double hydroxide (Fe3O4/Mg-Al-CO3-LDH) was prepared and used as porous support for ficin (EC 3.4.22.3) as a model enzyme. Structural characteristics were studied by XRD, FTIR, SEM and light scattering. The quantity of immobilized ficin on the mentioned LDH and non-magnetic LDH was measured and enzyme activity, stability and reusability were compared. Results revealed that the core and shell structure of Fe₃O₄/Mg-Al-CO₃-LDH makes it better dispersion compared to the pristine Mg-Al-CO₃-LDH. Ficin showed strong affinity to absorption of the surface of mentioned LDHs nanosheet especially magnetic LDH, confirmed that the existence of Fe₃O₄ in the core structure of magnetic Fe₃O₄/Mg-Al-CO₃-LDH caused better dispersion of LDH nanocrystal shell compared to pristine LDH moreover, enzyme which immobilized on the magnetic LDH supports, can be recovered by magnetic interaction. The storage stability of free ficin, immobilized ficin on the Mg-Al-CO₃-LDH and Fe₃O₄/Mg-Al-CO₃-LDH during a period of 120 days lost about 75%, 30%, and 20% of their initial activities, respectively.

Click Reaction-Mediated T2 Immunosensor for Ultrasensitive Detection of Pesticide Residues via Brush-like Nanostructure-Triggered Coordination Chemistry

We develop an ultrasensitive T₂-mediated immunosensor based on the coordination chemistry and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide andalkyne (CuAAC) and apply it for the detection of pesticide residues. We functionalize polyglutamic acid (PGA) on polystyrene to form a brush-like nanostructure that has a large loading capacity of Cu(II) through the coordination chemistry between PGA and Cu(II). Such a brush-like nanostructure could be used to chelate Cu(II) to modulate the CuAAC between azide-functionalized 1000 nm polystyrene (PS₁₀₀₀) and alkyne-functionalized 30 nm magnetic nanoparticles (MNP₃₀), and the MNP₃₀-PS₁₀₀₀ conjugate as a product of CuAAC can act as a magnetic probe in this T₂-based immunosensor. This click chemistry and coordination chemistry-mediated immunosensor allows for an ultrasensitive detection for chlorpyrifos residue (0.022 ng/mL), a 58-fold enhancement compared with that of enzyme-linked immunosorbent assay (1.28 ng/mL), providing a promising platform for detection of trace small molecules.

Production of Antigen-Binding Fragment against O,O-Diethyl Organophosphorus Pesticides and Molecular Dynamics Simulations of Antibody Recognition

Immunoassay for pesticides is an emerging analytical method since it is rapid, efficient, sensitive, and inexpensive. In this study, a recombinant antigen-binding fragment (Fab) against a broad set of O,O-diethyl organophosphorus pesticides (DOPs) was produced and characterized. The κ chain and Fd fragment were amplified via PCR and inserted into the vector pComb3XSS and the soluble Fab on phagemid pComb3XSS was induced by isopropyl β-d-thiogalactoside in E. coli TOP 10F’. SDS-PAGE, Western blotting, and indirect competitive ELISA results indicated that Fab maintained the good characteristics of the parental mAb. To better understand antibody recognition, the three-dimensional (3D) model of Fab was built via homologous modeling and the interaction between Fab and DOPs was studied via molecular docking and dynamics simulations. The model clearly explained the interaction manner of Fab and DOPs, and showed that the Arg-L96 and Arg-H52 were mainly responsible for antibody binding. This work provided a foundation for further mutagenesis of Fab to improve its characteristics.

A sensitive and validated immunomagnetic-bead based enzyme-linked immunosorbent assay for analyzing total T-2 (free and modified) toxins in shrimp tissues

Accurate analyses of total T-2 (free and modified) in aquatic organisms including shrimp are important as the hazard caused by T-2 has been caught increasing attention. Therefore, acurate analysis of free T-2 especially of modified T-2 in shrimp tissues is important. A rapid, sensitive, and validated method for quantitative determination of free T-2 and modified T-2 toxin was developed using immunomagnetic-bead based enzyme-linked immunosorbent assay (IMB-ELISA). Super paramagnetic particles with a carboxyl group activated by an ester method coupled with envelope antigen 3- acetylneosolaniol- hemisuccinate - ovalbumin (3-Ac-NEOS-HS-OVA) was used to form immunomagnetic beads which could bind to T-2 skeletal structure antibodies. The conditions for magnetic bead coating of T-2 skeletal structure antibodies, and the concentrations of the polyclonal antibody and HRP-labeled goat anti-rabbit antibody were optimized. A good linear relationship with T-2 concentrations ranging from 5-75ng/mL (R² =0.9965) was observed. The detection limit of different shrimp tissues of the IMB-ELISA ranged from 2.53 to 3.20ng/mL. And the IC₅₀ was 63ng/mL. The recovery varied from 86% to 99% with a standard deviation of 2.8-5.8%. The application of this method to study the distribution in tissues showed that the total T-2 concentration in hepatopancreas was 26.7µg/kg > blood > head > muscle in the highest dose group of 12.2mg/kg. Our research showed a combination of ELISA and immunomagnetic bead technology provide a new, convenient approach to significantly improve the accuracy and sensitivity of total T-2 measurement in shrimp tissues.

Nanocomposite biosensors for point-of-care—evaluation of food quality and safety

Nanosensors have wide applications in the food industry. Nanosensors based on quantum dots for heavy metal and organophosphate pesticides detection, and nanocomposites as indicators for shelf life of fish/meat products, have served as important tools for food quality and safety assessment. Luminescent labels consisting of NPs conjugated to aptamers have been popular for rapid detection of infectious and foodborne pathogens. Various detection technologies, including microelectromechanical systems for gas analytes, microarrays for genetically modified foods, and label-free nanosensors using nanowires, microcantilevers, and resonators are being applied extensively in the food industry. An interesting aspect of nanosensors has also been in the development of the electronic nose and electronic tongue for assessing organoleptic qualities, such as, odor and taste of food products. Real-time monitoring of food products for rapid screening, counterfeiting, and tracking has boosted ingenious, intelligent, and innovative packaging of food products. This chapter will give an overview of the contribution of nanotechnology-based biosensors in the food industry, ongoing research, technology advancements, regulatory guidelines, future challenges, and industrial outlook.

Rapid and sensitive detection of HIV-1 p24 antigen by immunomagnetic separation coupled with catalytic fluorescent immunoassay

In this study, a system of magnetic beads (MBs) coupled with catalytic fluorescent immunoassay for rapid and sensitive determination of HIV-1 capsid antigen p24 was developed. p24 was captured by antibody immobilized MBs, and the detection antibody was linked to horseradish peroxidase (HRP) through biotin-streptavidin recognition, catalyzing the oxidation of o-phenylenediamine (OPD) and hydrogen peroxide to produce a fluorescent product. This is the first reported utilization of the fluorescence of OPD oxidation product catalyzed by HRP for immunoassay. Optimization of conditions afforded a low detection limit of 0.5 pg/mL (3σ) for p24 with a linear range of 1.4-90.0 pg/mL. The assay exhibited good reproducibility with a relative standard deviation (RSD) of 4.4 %, 4.7 %, and 5.0 % for detecting 1.4 pg/mL, 22.5 pg/mL, and 45.0 pg/mL p24, respectively. The assay can be completed in less than 90 min. Moreover, the proposed method was successfully applied to detect p24 in spiked serum. This method overcomes the interference of MBs to the fluorescence signal and demonstrated higher sensitivity for detection of p24 than conventional ELISA kits. The system could be applied for detecting other antigens with high sensitivity, rapidity, specificity, and simple operation. Graphical Abstract A rapid and sensitive biosensing method coupling immunomagnetic separation and catalytic fluorescence for determination of HIV-1 p24 has been developed.

A Magnetic Nanoparticle Based Enzyme-Linked Immunosorbent Assay for Sensitive Quantification of Zearalenone in Cereal and Feed Samples

A novel enzyme-linked immunosorbent assay based on magnetic nanoparticles and biotin/streptavidin-HRP (MNP-bsELISA) was developed for rapid and sensitive detection of zearalenone (ZEN). The detection signal was enhanced and the sensitivity of the assay was improved by combined use of antibody-conjugated magnetic nanoparticles and biotin-streptavidin system. Under the optimized conditions, the regression equation for quantification of ZEN was y = −0.4287x + 0.3132 (R² = 0.9904). The working range was 0.07–2.41 ng/mL. The detection limit was 0.04 ng/mL and IC₅₀ was 0.37 ng/mL. The recovery rates of intra-assay and inter-assay ranged from 92.8%–111.9% and 91.7%–114.5%, respectively, in spiked corn samples. Coefficients of variation were less than 10% in both cases. Parallel analysis of cereal and feed samples showed good correlation between MNP-bsELISA and liquid chromatograph-tandem mass spectrometry (R² = 0.9283). We conclude that this method is suitable for rapid detection of zearalenone in cereal and feed samples in relevant laboratories.

A rapid immunomagnetic-bead-based immunoassay for triazophos analysis

Schematic illustration of a direct competitive immunomagnetic-bead-based enzyme-linked immunosorbent assay (IMB-ELISA) to detect the triazophos pesticides.

Development of a sensitive monoclonal antibody-based enzyme-linked immunosorbent assay for the analysis of paclobutrazol residue in wheat kernel

An indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed with monoclonal antibody (mAb) mAb6H73C9 recognizing the plant growth regulator paclobutrazol (PBZ). The icELISA had a half-maximum inhibition concentration (IC50) and working range of approximately 8.7 and 2.0-50.4 ng/mL, respectively. Average recoveries of PBZ in the wheat (Triticum aestivum) kernel samples were between 84.3 and 118.9% with relative standard deviations between 3.9 and 14.2%. As determined by the icELISA and further confirmed by liquid chromatography-electrospray ionization quadrupole Orbitrap mass spectrometry (LC-ESI-MS) analysis, the maximum residue concentration was about 0.07 mg/kg in the kernel samples, which indicated that PBZ could transfer from PBZ- treated seedlings to the kernel samples. The correlation coefficient (R(2)) between icELISA and LC-ESI-MS results was 0.979, which manifested that the developed icELISA was sensitive enough for monitoring PBZ residues in wheat kernels.

Integrated chip electrophoresis and magnetic particle isolation used for detection of hepatitis B virus oligonucleotides

Rapid and sensitive detection is a key step in the effective and early response to the global hazard of various viral diseases. In this study, an integrated isolation of hepatitis B virus (HBV)-specific DNA fragment by magnetic nanoparticles (MNPs) and its immediate analysis by microchip CGE was performed. Microfluidic CE chip was used to accommodate the complete process of viral DNA isolation by MNPs including hybridization and thermal denaturation followed by CE separation. Beforehand, calibration curves of HBV fragments were constructed. For isolation by MNPs, specific streptavidin-biotin interaction was used to bind complementary HBV fragment to magnetic particles. After analysis of isolated HBV by regular MNPs method, innovative approach was performed. The commercial CE chip (Bio-rad) was successfully used to execute HBV fragment isolation. Detection using LIF with detection limit of 1 ng/mL was accomplished.

Surface modification of magnetite nanoparticles using gluconic acid and their application in immobilized lipase

Superparamagnetic magnetite nanoparticles (SMN) were surface-modified with gluconic acid (GLA) to improve their hydrophilicity and bio-affinity. Gluconic acid was successfully coated on the surface of magnetite nanoparticles and characterized using Fourier transform infrared spectroscopy (FT-IR). With water-soluble carbodiimide (EDC) as the coupling reagent, lipase was successfully immobilized onto the hydroxyl-functionalized magnetic nanoparticles. The immobilized lipase had better resistance to temperature and pH inactivation in comparison to the free form and hence widened the reaction pH and temperature range. Thermostability and storage stability of the enzyme improved upon covalent immobilization. Immobilized lipase showed higher activity after recycling when compared to the free one and could be recovered by magnetic separation.

Dual-signal fenamithion probe by combining fluorescence with colorimetry based on Rhodamine B modified silver nanoparticles

A versatile yet simple strategy for the fabrication of a highly selective and sensitive fenamithion probe based on Rhodamine B (RB) modified silver nanoparticles (RB-Ag NPs) was developed. The advantage of our system over classical assays is that it combined fluorescence with colorimetry which can realize the prompt on-site and real-time detection of fenamithion with high sensitivity (0.1 nM) in aqueous solution. Moreover, the detection system presents excellent anti-disturbance ability when exposed to a series of interfering ionic/pesticides mixtures and can be applied to the determination of fenamithion in real vegetables and different water samples with the limit of detection (LOD) as low as 10 nM (0.0026 mg L(-1)), which is in accord with the maximum contamination level of 0.001∼0.25 mg L(-1) for organophosphorus pesticides as defined by the U.S. Environmental Protection Agency (EPA). Advantage is taken of the fact that RB would be displaced from the surface of the Ag NPs because of the stronger coordination ability of Ag NPs with fenamithion, an amino-containing organophosphorus pesticide, accompanying the clustered Ag NPs (9 nm) dissipating into smaller individual particles (7 nm). Based on this phenomenon, a novel analyte-induced etching mechanism was proposed.

Magnetic particles functionalized with PAMAM-dendrimers and antibodies: a new system for an ELISA method able to detect Ara h3/4 peanut allergen in foods

An innovative enzyme-linked immunosorbent assay (ELISA) format based on antibody-coated magnetic micro-particles (MPs) for the sensitive detection of Ara h3/4 allergen in food is described. The immunosupport is suspended in the incubation solutions and the MPs with the captured allergen can be easily harvested on a magnet, separated from the solutions, and washed using an easy-to-use, fast and selective approach that allows its detection and quantification. Two differently coated MPs, ProteinA-Pn-b and MP-NH(2)-PAMAM G 1.5-Pn-b immunosupports, were tested. The functionalization of the MPs with PAMAM-sodium carboxylate dendrimers elicits a major stability on the immunoglobulin activity resulting in a threefold enhancement of the analytical sensitivity for the assay with respect to a ProteinA immobilization. Validation was carried out on two different matrices: corn flakes and biscuits. In the case of MP-NH(2)-PAMAM G 1.5 -Pn-b immunosupport, limit of detection was found to be 0.2 mg peanuts/kg matrix in both matrices; the linear response range was demonstrated from 2.5 to 15 mg peanuts/kg matrix by performing statistical tests (homoscedasticity and Mandel fitting tests). Good accuracy and recovery (>80 +/- 2%) were obtained. Different food samples were tested and the results were compared with those obtained with a commercially available ELISA kit. The results obtained in this work demonstrated the applicability of the immunomagnetic ELISA methods on real samples and the possibility to perform the assay with significantly reduced reagent and sample consumption.