Characterization of Variable Region Genes and Discovery of Key Recognition Sites in the Complementarity Determining Regions of the Anti-Thiacloprid Monoclonal Antibody

Sequence-defined recombinant antibodies (rAbs) have emerged as alternatives to hybridoma-secreted monoclonal antibodies (mAbs) for performing immunoassays. However, the polyploidy nature of hybridomas often leads to the coexistence of aberrant or non-specific functional variable region (VR) gene transcripts, which complicates the identification of correct VR sequences. Herein, we introduced the use of LC-MS/MS combined with next-generation sequencing to characterize VR sequences in an anti-thiacloprid mAb, which was produced by a hybridoma with genetic antibody diversity. The certainty of VR sequences was verified by the functional analysis based on the recombinant antibody (rAb) expressed by HEK293 mammalian cells. The performance of the rAb was similar to that of the parental mAb, with IC50 values of 0.73 and 0.46 μg/L as measured by ELISAs. Moreover, molecular docking analysis revealed that Ser52 (H-CDR2), Trp98, and Trp93 (L-CDR3) residues in the complementarity determining regions (CDRs) of the identified VR sequences predominantly contributed to thiacloprid-specific recognition through hydrogen bonds and the CH-π interaction. Through single-site-directed alanine mutagenesis, we found that Trp98 and Trp93 (L-CDR3) showed high affinity to thiacloprid, while Ser52 (H-CDR2) had an auxiliary effect on the specific binding. This study presents an efficient and reliable way to determine the key recognition sites of hapten-specific mAbs, facilitating the improvement of antibody properties.

A fluorescence polarization immunoassay for detection of thiacloprid in environmental and agricultural samples

As a widely used neonicotinoid insecticide, thiacloprid has been observed to pose a risk to honeybees and the endocrine system of mammals. So a detection method with high sensitivity, simple operation and high throughput is required. Based on this consideration, we prepared an anti-thiacloprid monoclonal antibody (mAb, C9) and developed a fluorescence polarization immunoassay (FPIA) for the detection of thiacloprid. After optimizing the length of spacer and reaction conditions, the 50% inhibition concentration (IC₅₀), limit of detection (LOD) and linear range (IC₂₀ ∼ IC₈₀) of the FPIA are 15.34 ng mL⁻¹, 2.43 ng mL⁻¹ and 3.10–65.7 ng mL⁻¹, respectively. Meanwhile, FPIA just requires 12 min to detect the pesticide with simple operation. Then the FPIA was used to detect the thiacloprid in spiked rice, soil, cucumber and tomato samples, and recoveries were in the range of 79.1%–105.3% with 3.7%–12.3% standard deviation. The FPIA also shows good correlation with high-performance liquid chromatography for the detection of thiacloprid in tomato samples.

An anti-thiacloprid monoclonal antibody with high sensitivity was prepared and used to develop a fluorescence polarized immunoassay.

Highly efficient detection of salbutamol in environmental water samples by an enzyme immunoassay

Salbutamol (SAL) has potential hazardous effects on health, and has been found in natural water globally. To protect consumers from risks related to SAL residues, a fast and highly sensitive enzyme-linked immunosorbent assay (ELISA) was developed for the detection of SAL in environmental water samples. SAL hapten was synthesized and conjugated to proteins to be used as the immunogen for producing polyclonal antibodies. Under optimized conditions, the ELISA showed a 50% inhibitory concentration (IC₅₀ value) of 0.466μg/L, with a limit of detection (LOD, IC₁₀ value) of 0.021μg/L. The LOD of the ELISA was 5-fold lower than the maximum residue limits. The average recoveries of SAL from environmental samples, including tap water, river water and wastewater, ranged from 80.1 to 115.6%, which is well within the requirements of residue detection. Moreover, the results of the ELISA correlated well with high-performance liquid chromatography results, with a correlation coefficient of 0.988. These results suggest that the proposed ELISA method has potential application for the monitoring of SAL residues in environmental water samples.

Quantum-Dot-Based Lateral Flow Immunoassay for Detection of Neonicotinoid Residues in Tea Leaves

Neonicotinoid insecticides are commonly used for pest control on tea plantations as a result of their broad-spectrum activity. However, neonicotinoid residues released from tea leaves into tea infusions pose a dietary risk to consumers. Therefore, a rapid, sensitive, and reliable on-site detection method for neonicotinoids is needed. We developed a quantum-dot-based fluorescent lateral flow immunochromatographic strip (LFICS) combined with a broad-specific antibody for detection of typical neonicotinoids (imidacloprid, imidaclothiz, and clothianidin), with sensitivities [50% inhibitory concentration (IC₅₀)] of 0.104-0.33 ng/mL and visual detection limits of 0.5-1 ng/mL. The strip assay could be completed in less than 30 min. Using the LFICS to analyze spiked tea samples (green tea, black tea, and oolong tea), the average recovery of the three neonicotinoids ranged between 71 and 111%, with the coefficient of variation below 12%. The results from the LFICS tests for field samples were consistent with results from ultraperformance liquid chromatography-tandem mass spectrometry. The newly developed strip is a useful tool for the on-site detection of neonicotinoid residues in tea.

Mechanism of Neonicotinoid Toxicity: Impact on Oxidative Stress and Metabolism

Thousands of tons of neonicotinoids are widely used around the world as broad-spectrum systemic insecticides and veterinary drugs. Researchers originally thought that neonicotinoids exhibited low mammalian toxicity. However, following their widespread use, it became increasingly evident that neonicotinoids could have various toxic effects on vertebrates and invertebrates. The primary focus of this review is to summarize the research progress associated with oxidative stress as a plausible mechanism for neonicotinoid-induced toxicity as well as neonicotinoid metabolism. This review summarizes the research conducted over the past decade into the production of reactive oxygen species, reactive nitrogen species, and oxidative stress as aresult of neonicotinoid treatments, along with their correlation with the toxicity and metabolism of neonicotinoids. The metabolism of neonicotinoids and protection of various compounds against neonicotinoid-induced toxicity based on their antioxidative effects is also discussed. This review sheds new light on the critical roles of oxidative stress in neonicotinoid-induced toxicity to nontarget species.

Highly efficient detection of paclobutrazol in environmental water and soil samples by time-resolved fluoroimmunoassay

A fast and ultrasensitive indirect competitive time-resolved fluoroimmunoassay (TRFIA) was developed for the analysis of paclobutrazol in environmental water and soil samples. Paclobutrazol hapten was synthesized and conjugated to bovine serum albumin (BSA) for producing polyclonal antibodies. Under optimal conditions, the 50% inhibitory concentration (IC50 value) and limit of detection (LOD, IC20 value) were 1.09μgL(-1) and 0.067μgL(-1), respectively. The LOD of TRFIA was improved 30-fold compared to the already reported ELISA. There was almost no cross-reactivity of the antibody with the other structural analogues of triazole compounds, indicating that the antibody had high specificity. The average recoveries from spiked samples were in the range from 80.2% to 104.7% with a relative standard deviation of 1.0-9.5%. The TRFIA results for the real samples were in good agreement with that obtained by high-performance liquid chromatography analyses. The results indicate that the established TRFIA has potential application for screening paclobutrazol in environmental samples.

Rapid screening of flonicamid residues in environmental and agricultural samples by a sensitive enzyme immunoassay

A fast and sensitive polyclonal antibody-based enzyme-linked immunosorbent assay (ELISA) was developed for the analysis of flonicamid in environmental and agricultural samples. Two haptens of flonicamid differing in spacer arm length were synthesized and conjugated to proteins to be used as immunogens for the production of polyclonal antibodies. To obtain most sensitive combination of antibody/coating antigen, two antibodies were separately screened by homologous and heterologous assays. After optimization, the flonicamid ELISA showed that the 50% inhibitory concentration (IC50 value) was 3.86mgL(-1), and the limit of detection (IC20 value) was 0.032mgL(-1). There was no cross-reactivity to similar tested compounds. The recoveries obtained after the addition of standard flonicamid to the samples, including water, soil, carrot, apple and tomato, ranged from 79.3% to 116.4%. Moreover, the results of the ELISA for the spiked samples were largely consistent with the gas chromatography (R(2)=0.9891). The data showed that the proposed ELISA is an alternative tool for rapid, sensitive and accurate monitoring of flonicamid in environmental and agricultural samples.

Sensitive detection of thiacloprid in environmental and food samples by enhanced chemiluminescent enzyme immunoassay

A fast and sensitive enhanced chemiluminescent enzyme immunoassay (ECL-EIA) was developed based on horseradish peroxidase detected with a luminol-based substrate for neonicotinoid insecticide thiacloprid in environmental and food samples.

A new residue method for the determination of flonicamid in agricultural and environmental samples using enzyme immunoassay systems

An indirect competitive enzyme-linked immunosorbent assay (ELISA) for flonicamid was developed based on a polyclonal antibody.

Development of an enzyme-linked immunosorbent assay for thiacloprid in soil and agro-products with phage-displayed peptide

A monoclonal antibody (3A5) that can recognize thiacloprid was produced, and a linear 8-residue peptide phage library was constructed. Six phage-displayed peptides were isolated from the linear 8-residue peptide phage library and a cyclic 8-residue peptide phage library. A phage enzyme-linked immunosorbent assay (ELISA) was developed to detect thiacloprid using a phage-displayed peptide. Under the optimal conditions, the half-maximal inhibition concentration (IC50) and the limit of detection (IC10) of the developed phage ELISA were 8.3 and 0.7 μg/L, respectively. Compared with the conventional ELISA, the sensitivity was improved more than 3-fold. The cross-reactivity (CR) was less than 0.08% for the tested structural analogues and was regarded as negligible. The recoveries of thiacloprid ranged from 80.3% to 116.3% in environmental and agricultural samples, which conformed to the requirements for residue detection. The amount of thiacloprid detected by phage ELISA in the samples was significantly correlated with that detected by high-performance liquid chromatography. The current study indicates that isolating phage-displayed peptides from phage display libraries is an alternative method for the development of a sensitive immunoassay and that the developed assay is a potentially useful tool for detecting thiacloprid in environmental and agricultural samples.

A review of biosensing techniques for detection of trace carcinogen contamination in food products

Carcinogen contaminations in the food chain, for example heavy metal ions, pesticides, acrylamide, and mycotoxins, have caused serious health problems. A major objective of food-safety research is the identification and prevention of exposure to these carcinogens, because of their impossible-to-reverse tumorigenic effects. However, carcinogen detection is difficult because of their trace-level presence in food. Thus, reliable and accurate separation and determination methods are essential to protect food safety and human health. This paper summarizes the state of the art in separation and determination methods for analyzing carcinogen contamination, especially the advances in biosensing methods. Furthermore, the application of promising technology including nanomaterials, imprinted polymers, and microdevices is detailed. Challenges and perspectives are also discussed.