Automated flow fluorescent immunoassay for part per trillion detection of the neonicotinoid insecticide thiamethoxam

Novel ultrasensitive automated kinetic exclusion assay for measurement of plasma levels of soluble PD-L1, the predictive and prognostic biomarker in cancer patients treated with immune checkpoint inhibitors

Recently, the blood plasma or serum levels of soluble programmed death protein 1 (PD-L1), but not tissue PD-L1 expression level, have been proposed as an effective predictive and prognostic biomarker in patients treated with immune checkpoint inhibitors for different types of cancers. The quantification of soluble PD-L1 in blood will provide a quick evaluation of patients' immune status; however, the available assays have limitations in their sensitivity, reproducibility, and accuracy for use in clinical settings. To overcome these problems, this study was dedicated to developing an ultrasensitive automated flow-based kinetic exclusion assay (KinExA) for the accurate and precise measurement of soluble PD-L1 in plasma. The assay was developed with the assistance of KinExA™ 3200 biosensor. In this assay, PD-L1 in its calibrator or plasma sample solution was pre-equilibrated with anti-PD-L1 monoclonal antibody. The equilibrated mixture solution was then passed rapidly over PD-L1 protein that has been coated onto polymethylmethacrylate beads consolidated as a microcolumn in the observation cell of the KinExA™ biosensor. The free anti- PD-L1 antibody was bound to the immobilized PD-L1, however, the unbound molecules were removed from the beads microcolumn by flushing the system with phosphate-buffered saline. Fluorescein-labeled secondary antibody was passed rapidly over the beads, and the fluorescence signals were monitored during the flow of the labeled antibody through the beads. The calibration curve was generated by plotting the binding percentages as a function of PD-L1 concentrations in its sample solution. The working range of the assay with very a good correlation coefficient on a 4-parameter equation (r = 0.9992) was 0.5 - 100 pg mL─1. The assay limit of detection and quantitation were 0.15 and 0.5 pg mL─1, respectively. The recovery values of plasma-spiked PD-L1 were in the range of 96.4-104.3 % (±3.7-6.2 %). The precision of the assay was satisfactory; the values of the coefficient of variations did not exceed 6.2 % for both intra- and inter-day precision. The automated analysis by the proposed KinExA facilitates the processing of many specimens in clinical settings. The overall performance of the proposed KinExA is superior to the available assays for plasma levels of soluble PD-L1. The proposed assay is anticipated to have a great value in the measurement of PD-L1 where a more confident result is needed.

Novel electrochemiluminescence aptasensor based on AuNPs-ABEI encapsulated TiO2 nanorod for the detection of acetamiprid residues in vegetables

Gold nanoparticles (AuNPs)@N-(4-aminobutyl)-N-ethylisoluminol (ABEI)@Titanium dioxide nanorods (TiO2NRs) were used as sensing materials to produce a unique encapsulated nanostructure aptasensor for the detection of acetamiprid residues in this work. ABEI, an analog of luminol, was extensively used as an electrochemiluminescence (ECL) reagent. The ECL mechanism of ABEI- hydrogen peroxide (H2O2) system had connections to a number of oxygen-centered free radicals. TiO2NRs improved ECL response with high electron transfer and a specific surface area. AuNPs were easy to biolabel and could catalyze H2O2 to enhance ECL signal. AuNPs were wrapped around TiO2NRs by utilizing the reduction property of ABEI to form wrapped modified nanomaterials. The sulfhydryl-modified aptamer bound to the nanomaterial by forming gold-sulfur (Au-S) bonds. The aptamer selectively bound to its target with the addition of acetamiprid, which caused a considerable decrease in ECL intensity and enabled quantitative detection of acetamiprid. The aptasensor showed good stability, repeatability and specificity with a broad detection range (1×10-2-1×103 nM) and a lower limit of detection (3 pM) for acetamiprid residues in vegetables. Overall, this aptasensor presents a simple and highly sensitive method for ECL detecting acetamiprid, with potential applications in vegetable safety monitoring.

Recyclable Luminescence Sensor for Dinotefuran in Water by Stable Cadmium-Organic Framework

Due to the widespread use of dinotefuran around the world, its impact on food and environmental safety has aroused great concern, and the establishment of a rapid and convenient approach for dinotefuran detection is necessary but challenging. Herein, we synthesized a unique three-dimensional framework {[(CH₃)₂NH₂]₂[Cd₃(BCP)₂]·10H₂O·3.5DMF}_n (1). Single-crystal X-ray analysis indicates that 1 possesses a 4,8-connected anion framework that corresponds to alb topology, with a one-dimensional rectangular channel along the c-axis with the size of 4 Å × 10 Å. Compound 1 displays satisfactory solvent and thermal stability. Luminescent investigations reveal that 1 can selectively detect dinotefuran by fluorescence quenching among other pesticides, displaying excellent anti-interference performance with common ions in water. Importantly, the limit of detection is as low as 2.09 ppm, which is far below the residual concentration of the U.S. food standard. A fluorescence quenching mechanism study shows that there exists competitive energy absorption and static quenching processes. To our knowledge, 1 is the first MOF-based fluorescence probe for dinotefuran detection.

Immunochemical method for penthiopyrad detection through thermodynamic and kinetic characterization of monoclonal antibodies

Immunoassays are nowadays being employed for rapid contaminant analysis in clinical, environmental, and agrochemical samples. A thorough characterization of the antibody‒antigen interaction can bring light to the immunoreagent selection process in order to develop sensitive and robust tests. Thus, determination of equilibrium and reaction rate constants is usually recommendable. However, this can be quite tricky for low molecular weight compounds, and competitive strategies are commonly followed to estimate apparent affinity values. In the present study, a collection of monoclonal antibodies to penthiopyrad was raised for the first time, and apparent equilibrium constants were assessed by the Langmuir model using three different competitive enzyme-linked immunosorbent assay formats. The obtained K_D values from antibody-coated assays were quite close to the corresponding K_D values calculated from surface plasmon resonance (SPR) evaluation. These studies were employed to select a pair of immunoreagents for immunoassay development. The K_D value for penthiopyrad of the selected antibody obtained by SPR was 0.28 nM. The optimized direct assay showed an IC₅₀ value for penthiopyrad of 0.42 nM (0.15 ng mL^-1) in buffer. The limit of quantification for grape, must, and wine samples was 10 ng mL^-1. An excellent correlation was found when immunochemical results were compared with those from LC-MS/MS. As an application case, it was determined that 58% of penthiopyrad was still found in wine after fermentation.

Development of a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran by magnetic separation

The contents of both pesticide residues and dextran are important parameters for evaluating the quality of sugarcane. In this study, a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran was established on the basis of magnetic separation. Antigens of thiamethoxam and dextran were coupled to magnetic nanoparticles as the separation elements. Monoclonal antibodies of thiamethoxam (6C7D12) and dextran (3C6F7) were conjugated with the upconversion nanoparticles of NaYF₄:Yb,Er with an emission wavelength at 544 nm and NaYF₄:Yb,Tm with an emission wavelength at 477 nm to prepare the signaling elements, respectively. Due to the difference in the emission wavelength, the signaling elements bound on the separation elements could be detected simultaneously after separation by an external magnetic field. After optimization, the half-maximal inhibitory concentration (IC₅₀) values of the immunoassay for thiamethoxam and dextran were 0.46 and 49.33 ng mL⁻¹, respectively. The assay showed no cross-reactivity with the analogs of thiamethoxam and dextran except for clothianidin (8.7%). The average recoveries of thiamethoxam and dextran in sugarcane juice were 82.9–93.3% and 87.5–97.2%, respectively. The results indicated that the immunoassay could meet the requirements for the simultaneous quantitative detection of thiamethoxam and dextran.

The anti-thiamethoxam and anti-dextran monoclonal antibodies were prepared to develop a multicolor upconversion fluorescence immunoassay for the simultaneous determination of thiamethoxam (544 nm) and dextran (477 nm).

Electrocatalytic activity of the metallic silver electrode for thiamethoxam reduction: application for the detection of a neonicotinoid in tomato and orange samples

BACKGROUND

Thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro-4H-1,3,5-oxadiazin-4-imine) belongs to a relatively new class of insecticides known as neonicotinoids, which can block irreversibly nicotinic acetylcholine receptors of the nervous system of insects. Its determination at trace levels is an acute analytical problem. Therefore, chromatography, spectroscopy, and electrochemical technics were reported. These last have several advantages (simple sensitive and less expensive). This work investigated the electro-reduction of Thiamethoxam using simple and rapid method in real samples using metallic silver electrode.

RESULTS

Silver particles, known as effective catalysts in the reduction of nitro groups, were studied to explore their roles in the shift of thiamethoxam peak potential. Cyclic voltammetry, Tafel plot and electrochemical impedance spectroscopy analysis suggest that metallic silver electrodes have a significantly greater electrocatalytic activity in thiamethoxam electroreduction than glassy carbon electrodes and carbon paste electrodes. The electrocatalytic activity of metallic silver electrodes in thiamethoxam reduction was investigated by cyclic voltammetry and chronoamperometry. A linear variation in cathodic current with the square root of the scan rate was observed, suggesting that the process is diffusion controlled. Several supporting electrolytes were tested, and the best results were obtained with Britton-Robinson (BR) buffer, pH 10.4. A linear relationship between peak current and concentration was found in the range from 1.0 × 10^-5 to 1.0 × 10^-4  mol L^-1 using square wave voltammetry (SWV) with a correlation coefficient of 0.994. The detection limit and quantification limit were 5.49 × 10^-6 and 1.83 × 10^-5  mol L^-1 , respectively.

CONCLUSION

Silve metallic electrode exhibits efficient catalytic activity towards the Thiamethoxam reduction. The proposed electrode was then used for the determination of thiamethoxam in tomato anad orage juice samples. © 2019 Society of Chemical Industry.

Experimental and DFT studies on the vibrational, electronic spectra and NBO analysis of thiamethoxam

Vibrational and electronic spectral measurements were performed for 3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro) amine (thiamethoxam). Optimized geometrical structure and harmonic vibrational frequencies were calculated with ab initio RHF and DFT (B3LYP, CAMB3LYP, M06 and PBE1PBE) methods with 6-311++G (d, p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed in gas-phase using TD-B3LYP/6-311++G (d, p) approach and H2O solution using PCM-TD-B3LYP/6-311++G (d, p) approach. The calculated results matched well with the experimental values. Temperature dependence of thermodynamic parameters in the range of 100-1000 K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was discussed.

Review of enzyme-linked immunosorbent assays (ELISAs) for analyses of neonicotinoid insecticides in agro-environments

Immunoassay is a promising method that is suitable for rapid and simple analyses of pesticides, which are likely to persist at a trace level in agro-environments, including agricultural products, soil, and water. Particularly, enzyme-linked immunosorbent assay (ELISA) has wide application to development of analytical methods for pesticide residues because it can very sensitively and very accurately determine them in samples. This paper presents a review of the fundamental analytical performance, a device for the sample pretreatment methods before determination, and cases of applications to various samples on ELISA methods that have been developed for detection of neonicotinoid insecticides in food or environmental matrices. The reviewed ELISAs can be ranked as quantitative, rapid and simple analytical methods for single analytes. The recognition of ELISA as an analytical methodology for pesticide residues is expected to advance rapidly in the future.

Simultaneous determination of residues in pollen and high-fructose corn syrup from eight neonicotinoid insecticides by liquid chromatography-tandem mass spectrometry

The neonicotinoids have recently been identified as a potential contributing factor to the sudden decline in adult honeybee population, commonly known as colony collapse disorder (CCD). To protect the health of honeybees and other pollinators, a new, simple, and sensitive liquid chromatography-electrospray ionization mass spectrometry method was developed and validated for simultaneous determination of eight neonicotinoids, including acetamiprid, clothianidin, dinotefuran, flonicamid, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam, in pollen and high-fructose corn syrup (HFCS). In this method, eight neonicotinoids, along with their isotope-labeled internal standards, were extracted from 2 g of pollen or 5 g of HFCS using an optimized quick, easy, cheap, effective, rugged, and safe extraction procedure. The method limits of detection in pollen and HFCS matrices were 0.03 ng/g for acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam and ranged between 0.03 and 0.1 ng/g for nitenpyram and flonicamid. The precision and accuracy were well within the acceptable 20% range. Selectivity, linearity, lower limit of quantitation, matrix effect, recovery, and stability in autosampler were also evaluated during validation. This validated method has been used successfully in analyzing a set of pollen and HFCS samples collected for evaluating potential honeybee exposure to neonicotinoids.

Development of immunoassays for detecting clothianidin residue in agricultural products

Two enzyme-linked immunosorbent assays (ELISAs) based on polyclonal antibodies (PcAbs) for clothianidin are described: colorimetric detection format (ELISA) and pattern of chemiluminescent assay (CLEIA). Clothianidin hapten was synthesized and conjugated to bovine serum albumin (BSA) and ovalbumin (OVA) to produce immunogen and coating antigen. Anticlothianidin PcAbs were obtained from immunized New Zealand white rabbits. Under optimal conditions, the half-maximal inhibition concentration (IC₅₀) and the limit of detection (LOD, IC₂₀) of clothianidin were 0.046 and 0.0028 mg/L for the ELISA and 0.015 and 0.0014 mg/L for the CLEIA, respectively. There were no obvious cross-reactivities of the antibodies with its analogues except for dinotefuran. Recoveries of 76.4-116.4% for the immunoassays were achieved from spiked samples. The results of immunoassays for the spiked and authentic samples were largely consistent with gas chromatography. Therefore, the proposed immunoassays would be convenient and satisfactory analytical methods for the monitoring of clothianidin in agricultural products.

Immunoreagent generation and competitive assay development for cyprodinil analysis

Cyprodinil is an anilinopyrimidine fungicide applied worldwide for the prevention and treatment of highly destructive plant diseases in a large variety of crops, including cereals, fruits, and vegetables. This paper describes the development of the first reported immunoassays for cyprodinil. Two original haptens have been synthesized and conjugated to different carrier proteins, and polyclonal antibodies have been produced. Moreover, competitive enzyme-linked immunosorbent assays have been developed and characterized for the analysis of this widely used pesticide. The influence of organic solvents and buffer conditions over the assay analytical parameters was studied. The IC(50) values of the optimized immunoassays were 1.6 and 2.8 ng/mL for the direct and indirect formats, respectively. Quantitative recoveries were found using spiked apple and grape juice samples after a simple direct dilution, and a limit of quantification of 20 ng/mL for both fruit matrices was achieved. These immunoreagents could be very valuable for the sensitive, straightforward, and rapid monitoring of cyprodinil residues in foodstuffs.

Development of a sensitive Indirect Competitive Enzyme-Linked Immunosorbent Assay (ic-ELISA) based on the monoclonal antibody for the detection of the imidaclothiz residue

An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on monoclonal antibodies (MoAbs) for imidaclothiz was developed. The hapten of imidaclothiz was synthesized and conjugated to bovine serum albumin (BSA) and ovalbumin (OVA) to form the artificial antigens. MoAbs were obtained by immunizing BALB/c mice. Under the optimized conditions (10% methanol, 0.14 M Na(+), and pH 7.4), the half-maximal inhibition concentration (IC(50)) was 0.0875 ± 0.0034 mg/L and the limit of detection (IC(20)) was 0.0178 ± 0.0018 mg/L for imidaclothiz. There were no obvious cross-reactivities with most of the structural analogues of neonicotinoid insecticides, except imidacloprid. The recoveries of imidaclothiz in environmental and agricultural samples, including tap water, paddy water, soil, and cabbage, ranged from 80.43 to 113.83%, well within the requirements of residue detection. These results showed that this immunoassay could be used for the determination of imidaclothiz in environmental and agricultural samples.

Improved detectability and signal strength for rotating phase fluorescence immunoassays through image processing

Fluorescence immunoassays based on rotating solid phase have shown promise of lowered detection limits, among other advantages. However, intrinsic background distortion effects have limited their utility. Here, novel image processing strategies are used to minimize these effects and improve the estimate of concentration and lower the detection limit. This initial demonstration of a new processing capability is performed on data for a protein, myoglobin, which is a biomarker for acute myocardial infarction. For these data, compared with published results, the detection limit is improved by a factor of approximately one hundred (to 700 fM), which is competitive with or better than other immunoassay strategies (ELISA, for example) that are fully developed. This work suggests that image and video processing technologies can provide a valuable alternative approach to biochemical detection and concentration estimation.

Voltammetric determination of the neonicotinoid insecticide thiamethoxam using a tricresyl phosphate-based carbon paste electrode

The objective of the work was to investigate the possibility of using a tricresyl phosphate-based carbon paste electrode for the direct voltammetric determination of the neonicotinoid insecticide thiamethoxam. The analyte was determined by differential pulse voltammetry in Britton-Robinson buffer pH 7.0 in the concentration range of 3.72 - 41.5 ?g mL-1. The reproducibility of the analytical signal at the 7.29 ?g mL-1 level was characterized by a relative standard deviation of 1.3 %. The applicability of the developed method was evaluated by determining thiamethoxam in a river water sample and a commercial formulation Actara 25 WG.