Development of a phage chemiluminescent enzyme immunoassay with high sensitivity for the determination of imidaclothiz in agricultural and environmental samples

Development of an immunoassay based on a specific antibody for the detection of diphenyl ether herbicide fomesafen

Fomesafen belongs to the diphenyl ether herbicide, and is widely used in the control of broadleaf weeds in crop fields due to its high efficiency and good selectivity. The residual of fomesafen in soil has a toxic effect on subsequent sensitive crops and the microbial community structure because of its long residual period. Therefore, an efficient method for detecting fomesafen is critical to guide the correct and reasonable use of this herbicide. Rapid and sensitive immunoassay methods for fomesafen is unavailable due to the lack of specific antibody. In this study, a specific antibody for fomesafen was generated based on rational design of haptens and a sensitive immunoassay method was established. The half maximal inhibitory concentration (IC50) of the immunoassay was 39 ng/mL with a linear range (IC10-90) of 1.92-779.8 ng/mL. In addition, the developed assay had a good correlation with the standard UPLC-MS/MS both in the spike-recovery studies and in the detection of real soil samples. Overall, the developed indirect competitive enzyme immunoassay reported here is important for detecting and quantifying fomesafen contamination in soil and other environmental samples with good sensitivity and high reproducibility.

Broad-specificity monoclonal antibody against neonicotinoid insecticides via a multi-immunogen strategy and development of a highly sensitive GNP-based multi-residue immunoassay in ginseng and tomato

Neonicotinoid insecticides (NNIs) are extensively used across the agricultural products and foods. In order to meet the rapid detection requirements, a novel broad-specificity monoclonal antibody against NNIs was developed for the first time using a multi-immunogen strategy. The antibody's high affinity and its ability to bind target molecules were verified by ic-ELISA. Furthermore, molecular docking was used to evaluate the pivotal forces affecting binding affinity and to determine binding sites. Subsequently, a highly sensitive gold nanoparticle-based immunochromatographic assay was established for the rapid detection of eight NNIs and the IC₅₀ values were 0.03-1.61 ng/mL. The limits of detection for ginseng and tomato ranged from 0.76 to 30.19 μg/kg and 0.87 to 31.57 μg/kg, respectively. The spiked recovery ranged from 72.04% to 120.74%, and the coefficient of variation were less than 9.0%. This study provides a new direction for the development of multiple NNIs residue immunoassays.

Development of immunoassay based on a specific antibody for sensitive detection of nicosulfuron in environment

Nicosulfuron, one of the most widely used selective herbicides in corn field, can effectively control annual and perennial grass weeds, sedges, and some broadleaf weeds. The residual phytotoxicity of nicosulfuron in soil and water has become increasingly prominent. Therefore, an efficient method for detection of nicosulfuron was critical to ensure the sustainable and healthy development of agriculture and the ecological environment. In this paper, five nicosulfuron haptens which contained carboxyl group or aldehyde groups were designed and synthesized, and an indirect competitive immunoassay was developed for the first time. The assay showed an IC50 of 8.42 ng/mL and had negligible cross reactivities toward other sulfonylurea herbicides. In the spike and recovery studies, the recovery rate from soil samples was 95 %-104 %, and that of wheat roots was 92 %-98 %, which showed a good correlation with LC-MS analysis for nicosulfuron. The immunoassay was then used to quantify nicosulfuron concentration which could cause the obvious phytotoxic symptoms to wheat. Obvious symptoms of nicosulfuron phytotoxicity in wheat root was observed at the concentration of 0.068 ± 0.006 mg/kg (ELISA result) which was consistent with 0.072 ± 0.007 mg/kg obtained by LC-MS. The developed immunoassay method is an effective tool for environment contamination monitoring.

Comparison of Chemiluminescence Enzyme Immunoassay (Cl-ELISA) with Colorimetric Enzyme Immunoassay (Co-ELISA) for Imidacloprid Detection in Vegetables

Imidacloprid is one of the most commonly used insecticides for managing pests, thus, improving the quality and yield of vegetables. The abuse/misuse of imidacloprid contaminates the environment and threatens human health. To reduce the risk, a colorimetric enzyme-linked immunoassay assay (Co-ELISA) and chemiluminescence enzyme-linked immunoassay assay (Cl-ELISA) were established to detect imidacloprid residues in vegetables. The linear range of Co-ELISA ranged between 1.56 μg/L and 200 μg/L with a limit of detection (LOD) of 1.56 μg/L. The values for Cl-ELISA were 0.19 μg/L to 25 μg/L with an LOD of 0.19 μg/L, which are lower than those of Co-ELISA. Fortifying Chinese cabbage, cucumber, and zucchini with imidacloprid at 10, 50, and 100 μg/L yielded recoveries between 81.7 and 117.6% for Co-ELISA and at 5, 10, and 20 µg/L yielded recoveries range from 69.7 to 120.6% for Cl-ELISA. These results indicate that Cl-ELISA has a high sensitivity and a rapid detection time, saving cost (antigen and antibody concentrations) and serving as a more efficient model for the rapid detection of imidacloprid residue.

Development of competitive and noncompetitive immunoassays for clothianidin with high sensitivity and specificity using phage-displayed peptides

Clothianidin is a widely used pesticide that has been banned from outdoor use by the European Union due to its toxicity. To improve the sensitivity and specificity of existing clothianidin immunoassays, we developed competitive and noncompetitive immunoassays for clothianidin based on phage-displayed peptides. Cyclic 8-, 9-, and 10-residue peptide libraries were constructed using an optimized phagemid pComb-pVIII to prevent the loss of theoretical library diversity. Twenty-eight peptidomimetics and two anti-immunocomplex peptides were isolated through a blended panning process and used to develop competitive and noncompetitive phage enzyme-linked immunosorbent assays (P-ELISAs), respectively. After optimization, the half inhibition concentration (IC₅₀) and half saturation concentration (SC₅₀) of competitive and noncompetitive P-ELISAs were 3.83 ± 0.23 and 0.45 ± 0.02 ng/mL, respectively. Competitive P-ELISA showed 2.6-18.2% cross-reactivity with imidaclothiz, nitenpyram and imidacloprid. Importantly, noncompetitive P-ELISA, which has the best specificity and great sensitivity for clothianidin, showed no cross-reactivity with the analogs. The average recoveries of competitive and noncompetitive P-ELISAs were 73.8-104.1% and 76.6-102.2%, respectively, while the relative standard deviations were ≤ 11.0%. In addition, the results of P-ELISAs in the analysis of blind samples were consistent with those of high-performance liquid chromatography.

Binding Peptide-Promoted Biofunctionalization of Graphene Paper with Hydroxyapatite for Stimulating Osteogenic Differentiation of Mesenchymal Stem Cells

Graphene paper (GP), a macroscopic self-supporting material, has exceptional flexibility and preserves the excellent physical and chemical properties of graphene nanomaterials. But its applications in regenerative medicine remain to be further explored. Here, we biologically functionalized GP with hydroxyapatite (HA) nanorods by the use of GP-binding peptides as an affinity linker. This strategy solved two daunting challenges for regenerative medicine applications of GP: the lack of good hydrophilicity for supporting cell growth and the difficulty in forming composites by binding with nanobiomaterials. Briefly, we first screened a high-affinity GP-binding peptide (TWWNPRLVYFDY) by the phage display technique. Then we chemically conjugated the GP-binding peptide to the synthetic HA nanorods. The GP-binding peptide on the resultant HA nanorods enabled them to be bound and assembled onto the GP substrate with high affinity, forming a GP-peptide-HA composite with significantly improved hydrophilicity of GP. The composite promoted the attachment and proliferation of mesenchymal stem cells (MSCs), demonstrating its outstanding biocompatibility. Due to the unique compositions of the composite, it was also found to induce osteogenic differentiation of MSCs in vitro in the absence of other inducers in the medium, by verifying the expression of the osteogenic markers including collagen-1, bone morphogenetic proteins 2, runx-related transcription factor 2, osteocalcin, and alkaline phosphatase. Our work suggests that the GP-binding peptide can be used to link inorganic nanoparticles onto GP to facilitate the biomedical applications of GP.

Sortase-Mediated Phage Decoration for Analytical Applications

Phage-borne peptides and antibody fragments isolated from phage display libraries have proven to be versatile and valuable reagents for immunoassay development. Due to the lack of convenient and mild-condition methods for the labeling of the phage particles, isolated peptide/protein affinity ligands are commonly removed from the viral particles and conjugated to protein tracers or nanoparticles for analytical use. This abolishes the advantage of isolating ready-to-use affinity binders and creates the risk of affecting the polypeptide activity. To circumvent this problem, we optimized the phage display system to produce phage particles that express the affinity binder on pIII and a polyglycine short peptide fused to pVIII that allows the covalent attachment of tracer molecules employing sortase A. Using a llama heavy chain only variable domain (VHH) against the herbicide 2,4-D on pIII as the model, we showed that the phage can be extensively decorated with a rhodamine-LPETGG peptide conjugate or the protein nanoluciferase (Nluc) equipped with a C-terminal LPETGG peptide. The maximum labeling amounts of rhodamine-LPETGG and Nluc-LPETGG were 1238 ± 63 and 102 ± 16 per phage, respectively. The Nluc-labeled dual display phage was employed to develop a phage bioluminescent immunoassay (P-BLEIA) for the detection of 2,4-D. The limit of detection and 50% inhibition concentration of P-BLEIA were 0.491 and 2.15 ng mL^-1, respectively, which represent 16-fold and 8-fold improvement compared to the phage enzyme-linked immunosorbent assay. In addition, the P-BLEIA showed good accuracy for the detection of 2,4-D in spiked samples.

Uptake, Translocation, and Biotransformation of Neonicotinoid Imidaclothiz in Hydroponic Vegetables: Implications for Potential Intake Risks

Imidaclothiz is a novel and systemic neonicotinoid pesticide with excellent insecticidal efficacy. However, knowledge of its uptake, translocation, and biotransformation within plants is still largely unknown, restricting work on its accurate and comprehensive risk assessment. Here, we systematically investigated the behavior of imidaclothiz in three plant-water systems via hydroponic experiments. The results showed that imidaclothiz was readily taken up by plant roots and translocated upward, resulting in relative enrichment in leaves. The recoveries of imidaclothiz in plant-water systems decreased with increasing exposure time, and approximately 31.8-45.6% mass loss was measured at the end of exposure. Ultimately, imidaclothiz yielded five products in celery leaves, three products in lettuce leaves, and two products in radish leaves. Multiple metabolic reactions including hydroxylation, hydrolysis of nitrate ester, and methylation occurred within plants. This is the first report on the fate of imidaclothiz within plants and suggests increasing concerns about the risk assessment of imidaclothiz.

Quantification of silk protein using phage nanofibers with high binding specificity

Silk sericin (SS) has emerged as an important silk protein for use in medicine and textiles. However, no sensitive method is available for detecting it. Here, we employed phage nanofibers (∼7 nm wide) as a probe to quantify SS from a dilute aqueous solution by exploiting two properties of the bacteria-infecting phage nanofibers, its use as a platform for discovering SS-binding peptide and its ultrasensitive quantification by a simple titering assay (where the number of phage nanofibers displaying the SS-binding peptide is equal to the number of countable millimeter-sized plaques derived from the phage nanofibers by infecting bacteria through plating). We first discovered a SS-binding peptide and the phage nanofibers (SS-phage) displaying this peptide at the tip. We found that this peptide can even differentiate SS from another silk protein (silk fibroin), showing its high specificity. We then employed SS-phage nanofibers as a probe to bind the SS casted from the aqueous solution. Because SS-phage nanofibers bound to the SS and the SS in the original SS solution were numerically correlated and the number of SS-phage nanofibers can be determined by counting the plaques in a Petri dish by the titering assay, determining the number of phage-derived plaques with the naked eye led to the rapid quantification of SS concentration with a detection limit of 19.50 ng ml^-1. This phage-based counting strategy can be potentially applied to the facile detection of other proteins.

Development of immunoassays with high sensitivity for detecting imidacloprid in environment and agro-products using phage-borne peptides

Imidacloprid is the most widely used neonicotinoid insecticide and has been reported to pose a threat to ecological security and human health. Therefore, simple-to-operate and highly sensitive methods for the detection of trace levels of imidacloprid are necessary. Here, we isolated two phage-borne peptides that compete with imidacloprid to bind the monoclonal antibody (mAb) 3D11 from phage display peptide libraries. A phage-enzyme-linked immunosorbent assay (P-ELISA) and two phage time-resolved fluoroimmunoassays (P-TRFIAs) for the detection of imidacloprid were developed using the phage-borne peptides as substitutes for chemically synthesized antigens. After systematic optimization, the half-maximum inhibition concentrations (IC₅₀) of the P-ELISA, P-TRFIA-1, and P-TRFIA-2 were 0.067 ng mL^-1, 0.085 ng mL^-1, and 0.056 ng mL^-1, respectively. Based on their IC₅₀ values, the sensitivities of the P-ELISA and P-TRFIAs were more than four times greater than those of previous immunoassays. Additionally, the immunoassays showed satisfactory recovery in the detection of spiked samples and good correlation with high performance liquid chromatography (HPLC) for the detection of samples containing incurred residues.

Highly sensitive phage-magnetic-chemiluminescent enzyme immunoassay for determination of zearalenone

Here we demonstrate a novel phage-magnetic-chemiluminescent enzyme immunoassay (P-MCLEIA) for detection of zearalenone (ZEN). The P-MCLEIA was more efficient than conventional ELISA through several improvements. In the P-MCLEIA, magnetic nanoparticles were replaced of microplates as solid phases to reduce the whole incubation time within 40 min. Phage-mimotope was replaced of chemosynthetic antigen to improve the sensitivity of immunoassay. Chemiluminescence substrate was replaced of chromogenic substrate to further improve the sensitivity. The IC50 value of P-MCLEIA was 31.4 pg/mL, which was about 11 times lower than that of phage-magnetic-enzyme linked immunosorbent assay (P-MELISA) and 72 times lower than that of conventional ELISA. The LOD of P-MCLEIA was 4.3 pg/mL. Recovery study of P-MCLEIA was performed by analyzing ZEN levels in spiked corn samples, intra- and inter-assay recoveries were 80.0-119.8% and 82.7-112.7%, respectively. Furthermore, parallel analysis of natural corn samples showed a good correlation between the P-MCLEIA and high performance liquid chromatography.

Small Molecular Contaminant and Microorganism Can Be Simultaneously Detected Based on Nanobody-Phage: Using Carcinogen Aflatoxin and Its Main Fungal Aspergillus Section Flavi spp. in Stored Maize for Demonstration

Simultaneous detection technology has become a hot topic in analytical chemistry; however, very few reports on how to simultaneously detect small molecular contaminants and microorganisms have been in place. Aflatoxins are a group of highly toxic and carcinogenic compounds, which are produced mainly by Aspergillus flavus and Aspergillus parasiticus from section Flavi responsible for aflatoxin accumulation in stored cereals. Both aflatoxins and Aspergillus section Flavi were used to demonstrate the duplex real-time RCR method of simultaneously detecting small molecular contaminants and microorganisms. The detection of aflatoxins and Aspergillus section Flavi was carried out depending on the anti-idiotypic nanobody-phage V_2–5 and aflatoxin-synthesis related gene nor-1 (=aflD), respectively. The quantitative standard curves for simultaneous detection of aflatoxins and Aspergillus section Flavi were constructed, with detection limits of 0.02 ng/ml and 8 × 10² spores/g, respectively. Naturally contaminated maize samples (n = 25) were analyzed for a further validation. The results were in good agreement between the new developed method and the referential methods (high-performance liquid chromatography and the conventional plating counts).

Hapten Synthesis, Antibody Development, and a Highly Sensitive Indirect Competitive Chemiluminescent Enzyme Immunoassay for Detection of Dicamba

Although dicamba has long been one of the most widely used selective herbicides, some U.S. states have banned the sale and use of dicamba because of farmers complaints of drift and damage to nonresistant crops. To prevent illegal use of dicamba and allow monitoring of nonresistant crops, a rapid and sensitive method for detection of dicamba is critical. In this paper, three novel dicamba haptens with an aldehyde group were synthesized, conjugated to the carrier protein via a reductive-amination procedure and an indirect competitive chemiluminescent enzyme immunoassay (CLEIA) for dicamba was developed. The assay showed an IC50 of 0.874 ng/mL which was over 15 times lower than that of the conventional enzyme immunoassay. The immunoassay was used to quantify dicamba concentrations in field samples of soil and soybean obtained from fields sprayed with dicamba. The developed CLEIA showed an excellent correlation with LC-MS analysis in spike-and-recovery studies, as well as in real samples. The recovery of dicamba ranged from 86 to 108% in plant samples and from 105 to 107% in soil samples. Thus, this assay is a rapid and simple analytical tool for detecting and quantifying dicamba levels in environmental samples and potentially a great tool for on-site crop and field monitoring.

Competitive and noncompetitive immunoassays for the detection of benzothiostrobin using magnetic nanoparticles and fluorescein isothiocyanate-labeled peptides

Phage-displayed peptides have been proven to be powerful reagents for competitive and noncompetitive immunoassays. However, they are unconventional reagents, which greatly limit their analytical commercial applications and require additional reagents for detection. In this work, the peptides that specifically bind with anti-benzothiostrobin monoclonal antibody (mAb) or benzothiostrobin-mAb immunocomplex were synthesized and conjugated with fluorescein isothiocyanate (FITC) as substitutes of the phage-displayed peptides to avoid their shortcomings and extend their applications. Competitive and noncompetitive fluorescence immunoassays (FIAs) for benzothiostrobin were developed by mAb coupling with magnetic nanoparticles as concentration elements and peptides conjugated with FITC as tracers. Compared with enzyme-linked immunosorbent assays, the FIAs reduced the number of steps from 6 to 2 and analysis time from more than 5 to 1.2 h. The competitive FIA showed the half-maximal inhibition concentration (IC₅₀) of 16.8 ng mL^-1 and detection range (IC₁₀-IC₉₀) of 1.0-759.9 ng mL^-1, while the concentration of analyte producing 50% saturation of the signal (SC₅₀) and detection range (SC₁₀-SC₉₀) of noncompetitive FIA were 93.4 and 5.9-788.2 ng mL^-1, respectively. The average spiked recoveries were 68.33-98.50% and 73.33-96.67% for competitive and noncompetitive FIAs, respectively. The FIAs showed good correlation with high-performance liquid chromatography for the detection of benzothiostrobin in authentic samples. Graphical abstract Development of competitive and noncompetitive fluorescence immunoassays for benzothiostrobin by using monoclonal antibody coupling with magnetic nanoparticles as concentration elements and peptides conjugated with fluorescein isothiocyanate as tracers.