Development of an immunoassay for carbendazim based on a class-selective monoclonal antibody

Development of a Lateral Flow Immunoassay Based on a Highly Specific Monoclonal Antibody To Detect 4-Methylaminoantipyrine

To avoid false-positive results in immunoassays due to cross-reactivity of antibodies with structural analogues, especially metabolites of target compounds, the preparation of highly specific antibodies is crucial. Preserving the characteristic structure of a target compound when designing a hapten is important when preparing highly specific antibodies. Here, we designed a novel hapten, 4-(((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4yl)amino)methyl)benzoic acid, named AA-BA, to improve the specificity of antibodies for detection of 4-methylaminoantipyrine (MAA), a residual marker of dipyrone, an important antipyretic-analgesic and anti-inflammatory drug. The structural features of the hapten remained almost the same as those of MAA. After experimental validation, monoclonal antibody 6A4 (mAb 6A4) was prepared with the half maximal inhibitory concentration (IC₅₀) value of 4.03 ng/mL and negligible cross-reactivity with dipyrone metabolites and other antibiotics. In addition, a specific lateral flow immunoassay (LFA) strip based on colloidal gold was developed for screening MAA with a cutoff value of 25 ng/mL in milk. The developed LFA is a useful tool for rapid and accurate detection of MAA.

Carbendazim toxicity in different cell lines and mammalian tissues

The extensive production and use of harmful pesticides in agriculture to improve crop yield has raised concerns about their potential threat to living components of the environment. Pesticides cause serious environmental and health problems both to humans and animals. Carbendazim (CBZ) is a broad spectrum fungicide that is used to control or effectively kill pathogenic microorganisms. CBZ is a significant contaminant found in food, soil and water. It exerts immediate and delayed harmful effects on humans, invertebrates, aquatic animals and soil microbes when used extensively and repeatedly. CBZ is a teratogenic, mutagenic and aneugenic agent that imparts its toxicity by enhancing generation of reactive oxygen species generation. It elevates the oxidation of thiols, proteins and lipids and decreases the activities of antioxidant enzymes. CBZ is cytotoxic causing hematological abnormalities, mitotic spindle deformity, inhibits mitosis and alters cell cycle events which lead to apoptosis. CBZ is known to cause endocrine-disruption, embryo toxicity, infertility, hepatic dysfunction and has been reported to be one of the leading causes of neurodegenerative disorders. CBZ is dangerous to human health, the most common side effects upon chronic exposure are thyroid gland dysfunction and oxidative hepato-nephrotoxicity. In mammals, CBZ has been shown to disrupt the antioxidant defense system. In this review, CBZ-induced toxicity in different cells, tissues and organisms, under in vitro and in vivo conditions, has been systematically discussed.

A Competitive Assay Based on Dual-Mode Au@Pt-DNA Biosensors for On-Site Sensitive Determination of Carbendazim Fungicide in Agricultural Products

Carbendazim (CBZ), a systemic, broad-spectrum benzimidazole fungicide, is widely used to control fungal diseases in agricultural products. Its residues might pose risks to human health and the environment. Therefore, it is warranted to establish a rapid and reliable method for its residual quantification. Herein, we proposed a competitive assay that combined aptamer (DNA) specific recognition and bimetallic nanozyme gold@platinum (Au@Pt) catalysis to trace the CBZ residue. The DNA was labeled onto bimetallic nanozyme Au@Pt surface to produce Au@Pt probes (Au@Pt-DNA). The magnetic Fe₃O₄ was functionalized with a complementary strand of DNA (C-DNA) to form Fe₃O₄ probes (Fe₃O₄-C-DNA). Subsequently, the CBZ and the Fe₃O₄ probes competitively react with Au@Pt probes to form two Au@Pt-DNA biosensors (Au@Pt-ssDNA-CBZ and Au@Pt-dsDNA-Fe₃O₄). The Au@Pt-ssDNA-CBZ biosensor was designed for qualitative analysis through a naked-eye visualization strategy in the presence of CBZ. Meanwhile, Au@Pt-dsDNA-Fe₃O₄ biosensor was developed to quantitatively analyze CBZ using a multifunctional microplate reader. A competitive assay based on the dual-mode Au@Pt-DNA biosensors was established for onsite sensitive determination of CBZ. The limit of detection (LOD) and recoveries of the developed assay were 0.038 ng/mg and 71.88-110.11%, with relative standard deviations (RSDs) ranging between 3.15 and 10.91%. The assay demonstrated a good correlation with data acquired from liquid chromatography coupled with mass spectrometry/mass spectrometry analysis. In summary, the proposed competitive assay based on dual-mode Au@Pt-DNA biosensors might have a great potential for onsite sensitive detection of pesticides in agro-products.

A multicolor enzyme-linked immunoassay method for visual readout of carbendazim

Enzyme-linked immunosorbent assay (ELISA) with high specificity and sensitivity is one of the most popular techniques for detecting carbendazim (CBD), a commonly used benzimidazole fungicide in agriculture. However, the traditional ELISA based on the horseradish peroxidase (HRP)-3,3',5,5'-tetramethylbenzidine (TMB) system for CBD only displays the yellow color of TMB²⁺ from deep to light, making it difficult for the naked eye to judge whether CBD in fruits and vegetables exceeds the maximum residue limit. In this article, we intend to improve the traditional ELISA method to establish a multicolor signal output ELISA to achieve visual semiquantitative detection of CBD. This method is based on the optical properties of gold nanorods (AuNRs). After introducing AuNRs into TMB²⁺ solution, which was produced by the HRP-TMB system of traditional ELISA, AuNRs were quickly etched by TMB²⁺. Consequently, the longitudinal localized surface plasmon resonance peak of AuNRs shows a clear blue shift and a vivid color change. Different concentrations of CBD generate different amounts of TMB²⁺, which in turn leads to different etching degrees of AuNRs, and ultimately results in a rainbow-like color change. As a result, CBD from 0.08 to 100 ng mL^-1 can be easily distinguished by the naked eye, which does not require any large instruments. Moreover, the colors displayed by 0.49 ng mL^-1 (purple) and 0 ng mL^-1 (pink) are significantly different from each other. It should be noted that 0.49 ng mL^-1 is far below the most stringent maximum residue limit of CBD in the world. Additionally, the quantitative determination of CBD spiked in canned citrus, citrus fruits, chives, and cabbage samples showed satisfactory recoveries. The good performance of the AuNR-based ELISA makes it have a wide range of application prospects in food safety and international trade.

A silver@gold nanoparticle tetrahedron biosensor for multiple pesticides detection based on surface-enhanced Raman scattering

The detection of multiple pesticides in food and environment is of great importance for human health and safety. In this study, the DNA backbone structure and Ag@Au nanoparticles (NPs) to construct a nano-tetrahedron with the help of the surface-enhanced Raman scattering (SERS) effect by controlling the formation of SERS hotspots and subsequently realized the simultaneous detection of multiple pesticides. The DNA aptamers corresponding to the three pesticides of profenofos, acetamiprid and carbendazim were embedded into the three edges of the DNA tetrahedral skeleton, and the tetrahedral corners were connected to modify the Ag@Au NPs with different Raman signaling molecules. When aptamers recognize the related pesticides, the DNA backbone is deformed. Then Ag@Au NPs approach to each other with SERS hotspots formed and the intensity of the Raman signal increased, realizing the detection of the pesticide content. The biosensor constructed from the SERS substrate with higher sensitivity and lower detection limit (profenofos: 0.0021 ng mL^-1; acetamiprid: 0.0046 ng mL^-1; carbendazim: 0.0061 ng mL^-1). The practicability of this proposed method was verified by adding the recovery rate detection and the accuracy of the method was examined by the analysis of the HPLC-MS method. The proposed SERS biosensor could distinguish and detect three pesticides in food and environmental samples with high sensitivity and low detection limit that can be used in practical applications.

Colloidal gold-based lateral flow immunoassay with inline cleanup for rapid on-site screening of carbendazim in functional foods

In this study, for the first time, we propose a sensitive colloidal gold-based lateral flow immunoassay (LFIA) that can be used to detect carbendazim residues in functional foods. The adoption of inline cleanup LFIA strips effectively improved background interference to reduce misjudgment of results. First, the hapten 2-(methylamino)-1H-benzo[d]imidazole-5-carboxylic acid was used to establish the carbendazim immunoassay method. Subsequently, colloidal gold-mAb preparation and LFIA detection conditions were systematically optimized. For root and fruit samples (ginseng, ginger, jujube, and Chinese wolfberry), the designed strips had a cutoff value of 8 ng/mL. For flower and seed samples (chrysanthemum, coix seed, and malt), the cutoff value was 12 ng/mL. Even in a complex matrix, the established LFIA method demonstrates satisfactory sensitivity and anti-interference ability. This method was successfully applied in detection of carbendazim residues in complex functional foods, and the assay results are consistent with those obtained via liquid chromatography-tandem mass spectrometry. In short, the proposed method is fast and sensitive and has strong anti-interference ability. Furthermore, it provides a new technical method highly relevant to the on-site rapid detection of carbendazim residues in complex sample matrix.

Molecularly imprinted microspheres based multiplexed fluorescence method for simultaneous detection of benzimidazoles and pyrethroids in meat samples

Two molecularly imprinted microspheres and two fluorescent tracers for benzimidazoles and pyrethroids were synthesized respectively. The two types of microspheres were coated in the wells of conventional microplate simultaneously. Then the sample extracts and the two traces were added for differential competition. The fluorescence intensities at two different emission wavelengths were excited and recorded for quantification of the two classes of drugs respectively. The optimized multiplexed fluorescence method could be used to determine 8 benzimidazoles and 10 pyrethroids in mutton and beef samples simultaneously. The limits of detection of the method for the 18 drugs were in the range of 5.2-17 ng/mL, and the recoveries from the standards fortified blank samples were in the range of 67.7%-109%. From the analysis of 60 real mutton and beef samples, this method could be used for multi-screening the residues of benzimidazoles and pyrethroids in meat samples.

Highly Specific Monoclonal Antibody and Sensitive Quantum Dot Beads-Based Fluorescence Immunochromatographic Test Strip for Tebuconazole Assay in Agricultural Products

A monoclonal antibody (mAb) was raised against tebuconazole (TEB) using a hapten where the p-chloro substituent of the TEB molecule was replaced with a long-chain carboxylic acid. The resulting mAb showed high sensitivity and specificity against TEB characterized by ELISA with a half-maximal inhibitory concentration (IC50) of 0.19 ng mL-1 and with cross-reactivity (CR) values below 0.01% to several analogues of triazole fungicides. On the basis of the mAb produced, a quantum dot beads-based fluorescence immunochromatographic test strip assay (QBs-FITSA) was developed for rapid and sensitive detection of TEB in agricultural product samples. The QBs-FITSA exhibited a linear detection range from 0.02 to 1.25 ng mL-1 with a limit of detection (LOD) of 0.02 ng mL-1. Furthermore, using produced mAb, multiple high-throughput rapid immunoassay formats could be achieved as a convenient monitoring tool for evaluation of human and environmental exposure to TEB.

Preparation of a chemiluminescence sensor for multi-detection of benzimidazoles in meat based on molecularly imprinted polymer

In this study, a molecularly imprinted polymer capable of recognizing 8 benzimidazoles was first synthesized. The computation simulation showed that the shape and size of used template were the main factors influencing its recognition ability. Then the polymer was used as recognition reagent to prepare a chemiluminescence sensor on conventional 96-well microplate. The sample solution and a HRP-labeled hapten were added into the microplate wells to perform competitive binding, and the light signal was initiated with 4-(imidazol-1-yl)phenol enhanced luminol-H₂O₂ system. The optimized sensor was used to determine the residues of 8 benzimidazoles in mutton and beef. Result showed that the sensor achieved ultrahigh sensitivity (limits of detection of 1.5-21 pg/mL), rapid assay process (18 min) and satisfactory recovery (65.8%-91.2%). Furthermore, this sensor could be reused for 4 times. Therefore, this sensor could be used as a rapid, simple, sensitive and durable tool for screening the residual benzimidazoles in meat.

Superabsorbent hydrogels coating increased degradation and decreased bound residues formation of carbendazim in soil

The intensive use of pesticides has caused serious environmental pollution and ecological issues. Thus, it is imperative to explore an efficient way to minimize the pesticide residues and pollution. In the present study, we employed the superabsorbent hydrogels (SHs)-coated pesticide ¹⁴C-carbendazim (H-¹⁴C-MBC) to investigate the fate of MBC in aerobic soils and to assess the soil microbial state during incubation. The results showed that after coating with SHs, MBC dissipation was improved significantly by 34.2-54.1% compared with that in the control (p<0.05), reducing the persistence of MBC in soil matrix. At 100d, the release of ¹⁴C-CO₂ was enhanced by 68.0% and 46.6% in neutral loamy soil and basic saline soil, respectively, with respect to the control, resulting in more complete degradation and detoxification of MBC. Additionally, the bound residue in soils, which was associated with potential environmental risk and pollution, was reduced by 15.2% and 14.2%, respectively, compared with that in control soils. The microbial diversity of post-H-¹⁴C-MBC soil varied, and microbial composition and abundance remained different from the control, even with the refreshment of soil stability and fertility compared with the blank soil. These results demonstrate the environmental behavior of SHs-coated MBC in soils, and illustrate that SHs-encapsulated formulations would be a promising measure for reducing the soil-residue pollution and environmental risk of pesticides.

Gold Nanoparticle-Based Paper Sensor for Simultaneous Detection of 11 Benzimidazoles by One Monoclonal Antibody

A colloidal gold immunochromatographic assay based on a generic monoclonal antibody is developed for the simultaneous detection of benzimidazoles and metabolite residues in milk samples. The monoclonal antibody is prepared using 2-(methoxycarbonylamino)-3H-benzimidazole-5-carboxylic acid as the hapten, and it can recognize 11 types of benzimidazoles simultaneously. The immunochromatographic strip is assembled and labeled using gold nanoparticles. This strip can detect 11 benzimidazoles including albendazole, albendazole s-oxide, albendazole sulfone, fenbendazole, fenbendazole sulfone, flubendazole, mebendazole, parbendazole, oxfendazole, oxibendazole, and carbendazim within 15 min in milk samples. Results are obtained visually with the naked eye, and the cutoff values and the visual limit of detection values for these benzimidazoles are 25, 6.25, 12.5, 12.5, 50, 25, 50, 50, 50, 6.25, and 25 ng mL^-1 , and 6.25, 3.125, 3.125, 1.56, 12.5, 6.25, 12.5, 12.5, 6.25, 0.78, and 12.5 ng mL^-1 , respectively. Results are also obtained using a hand-held strip scan reader, with calculated limit of detection values for these benzimidazoles of 0.83, 0.77, 1.83, 0.98, 7.67, 3.50, 3.96, 5.71, 0.92, 0.59, and 1.69 ng mL^-1 , respectively. In short, the developed paper sensor is a useful tool for rapid and simple screening of residues of benzimidazoles in milk samples.

Selection and Characterization of DNA Aptamers for Electrochemical Biosensing of Carbendazim

This article reports a novel aptamer-based impedimetric detection of carbendazim, a commonly used benzimidazole fungicide in agriculture. High affinity and specificity DNA aptamers against carbendazim were successfully selected using systematic evolution of ligand by exponential enrichment (SELEX). The dissociation constants (K_ds) of the selected DNA aptamers after 10 in vitro selection cycles were characterized using fluorescence-based assays showing values in the nanomolar range. The aptamer which showed the highest degree of affinity and conformation change was used to fabricate an electrochemical aptasensor via self-assembly of thiol-modified aptamer on gold electrodes. The aptasensor exploits the specific recognition of carbendazim by the aptamer immobilized on the gold surface which leads to conformational changes in the aptamer structure. This conformational change alters the access of a ferrocyanide/ferricyanide redox couple to the aptasensor surface. The aptasensor response is thus measured by following the increase in the electron transfer resistance of the redox couple using Faradaic electrochemical impedance spectroscopy. This method allowed a selective and sensitive label-free detection of carbendazim within a range of 10 pg/mL-10 ng/mL with a limit of detection of 8.2 pg/mL. The aptasensor did not show cross reactivity with other commonly used pesticides such as fenamiphos, isoproturon, atrazine, linuron, thiamethoxam, trifluralin, carbaryl, and methyl parathion. Moreover, the aptasensor has been applied in different spiked food matrixes showing high recovery percentages. We believe that the proposed aptasensor is a promising alternative to the currently used methods for carbendazim monitoring.

SERS encoded nanoparticle heterodimers for the ultrasensitive detection of folic acid

In this paper, gold–silver nanoparticle (AuNP–AgNP) heterodimers were assembled with highly yield as an active SERS substrate, based on antigen–antibody immunoreaction. The developed SERS sensor has successful achieved the ultrasensitive detection of folic acid (FA) with the limit of detection (LOD) as 0.86 pg/mL. And the linear range was from 0.005 ng/mL to 1 ng/mL. The results also demonstrated that this developed method showed high specificity and excellent recovery for the human serum samples, indicating its promising potential in bio-diagnosis and the environmental monitoring.