Novel immunochromatographic strip assay based on up-conversion nanoparticles for sensitive detection of imidacloprid in agricultural and environmental samples

A sensitive fluoroimmunoassay for quantitative detection of imidacloprid based on quantum dot-streptavidin conjugate

Imidacloprid (IMI), the most commonly used neonicotinoid, is widely present in both the environment and agro-products due to extensive and prolonged application, posing potential risks to ecological security and human health. This study introduced a sensitive and rapid fluorescence-linked immunosorbent assay, employing Quantum Dot-Streptavidin conjugate (QDs-SA-FLISA), for efficient monitoring of IMI residues in agro-products. Under optimized conditions, the QDs-SA-FLISA exhibited a half-maximal inhibition concentration (IC50) of 1.70 ng/mL and a limit of detection (LOD, IC20) of 0.5 ng/mL. Investigation into the sensitivity enhancement effect of the QDs-SA revealed that the sensitivity (IC50) of the QDs-SA-FLISA was 7.3 times higher than that of ELISA. The recoveries and relative standard deviation (RSD) ranged from 81.7 to 118.1 % and 0.5-9.4 %, respectively, for IMI in brown rice, tomato and pear. There was no significant difference in IMI residues obtained between QDs-SA-FLISA and UHPLC-MS/MS. Thus, the QDs-SA-FLISA represents a reliable approach for the quantitative determination of IMI in agro-products.

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.

Lateral flow immunoassays for antigens, antibodies and haptens detection

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

Enhanced Lateral Flow Immunoassay with Double Competition and Two Kinds of Nanoparticles Conjugates for Control of Insecticide Imidacloprid in Honey

Finding optimal conditions for competitive lateral flow immunoassay is a controversial task. The content of specific antibodies labeled by nanoparticles should be simultaneously high to reach intense signals and low to register an influence on the signals for minimal concentrations of the target analyte. We propose to use two kinds of complexes of gold nanoparticles in the assay, with antigen-protein conjugates and with specific antibodies. The first complex interacts both with immobilized antibodies in the test zone and with antibodies on the surface of the second complex. In this assay, the coloration is enhanced by the binding of two-colored preparations in the test zone, whereas the antigen in the sample inhibits both the binding of the first conjugate with the immobilized antibodies and with the second conjugate. This approach is realized for the detection of insecticide imidacloprid (IMD), an important toxic contaminant connected with the recent global death of bees. The proposed technique expands the working range of the assay, that is, in accordance with its theoretical analysis. The reliable change of coloration intensity is achieved for a 2.3-times-lower concentration of the analyte. The limit of IMD detection is 0.13 ng/mL for tested solutions and 1.2 µg/kg for initial honey samples. The combination of two conjugates doubles the coloration in the absence of the analyte. The developed lateral flow immunoassay is applicable for five-fold-diluted honey samples without extraction, does not require additional stages (all reagents are pre-applied to the test strip), and is implemented in 10 min.

Enhancement of the sensing performance and stability of a MOF based-molecularly imprinted polymer by utilizing dual-ligands and triethanolamine catalysis

In this work, a terbium MOF-based molecularly imprinted polymer (Tb-MOF@SiO₂@MIP) was prepared using two ligands as organic linkers and triethanolamine (TEA) as a catalyst to improve the sensing performance and stability of the fluorescence sensors. The obtained Tb-MOF@SiO₂@MIP was then characterized using a transmission electron microscope (TEM), energy dispersive spectroscopy (EDS) Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). The results revealed that Tb-MOF@SiO₂@MIP was successfully synthesized with a thin imprinted layer of 76 nm. The synthesized Tb-MOF@SiO₂@MIP maintained 96% of its original fluorescence intensity after 44 days in aqueous environments because of appropriate coordination models between the imidazole ligands as a nitrogen donor and Tb (Ⅲ). Furthermore, TGA analysis results indicated that an increase in the thermal stability of Tb-MOF@SiO₂@MIP was attributed to the thermal barrier from a MIP layer. The Tb-MOF@SiO₂@MIP sensor responded well to the addition of imidacloprid (IDP) in the range of 2.07-150 ng mL^-1 with a low detection limit of 0.67 ng mL^-1. In vegetable samples, the sensor can quickly detect IDP levels with the average recovery ranging from 85.10 to 99.85% and RSD values ranging from 0.59 to 5.82%. The UV-vis absorption spectrum and density functional theory analysis results revealed that the inner filter effect and dynamic quenching process both contributed to the sensing process of Tb-MOF@SiO₂@MIP.

Simultaneous, Label-Free and High-throughput SERS Detection of Multiple Pesticides on Ag@Three-Dimensional Silica Photonic Microsphere Array

Rapid identification and quantitative simultaneous analysis for multiple pesticide in real samples based on surface-enhanced Raman spectroscopy (SERS) is still a challenge because of sample complexity, reproducibility, and stability of SERS substrate. With use of colloidal silver nanoparticles loaded three-dimensional (3D) silica photonic microspheres (SPMs) array as the analytical platform, a SERS-based array assay for multiple pesticides was developed in this work. The silver nanoparticles were fixed into the gaps formed by the self-assembled nanospheres of the 3D SPMs to produce "hot spots", on which the Raman enhanced effect was up to 9.86 × 10⁷ and the maximum electric field enhancement effect reached to 9.75 times, ensuring the target pesticides on the surface of the SERS-substrate integrated SPM can be detected sensitively. Using 2,4-dichlorophenoxyacetic acid (2,4-D), glyphosate, and imidacloprid as the testing pesticides, the label-free and high-throughput SERS assay for simultaneous detection of the pesticides was established, giving good linear detection ranges (0.1-204.8 μg/mL for 2,4-D, 0.3-247.9 μg/mL for glyphosate, and 0.2-204.8 μg/mL for imidacloprid) and low detection limits (3.03 ng/mL for 2,4-D, 3.14 ng/mL for glyphosate, and 8.82 ng/mL for imidacloprid). The spiked recovery rates in the real samples were measured in the range of 82-112%, which was consistent with that of the classical standard methods. The label-free 3D SERS array analytical platform provides a powerful tool for high-throughput and low-cost screening of multiple pesticide residues in real samples.

A Monoclonal Antibody-Based Immunochromatographic Test Strip and Its Application in the Rapid Detection of Cucumber Green Mottle Mosaic Virus

Two specific monoclonal antibodies (mAbs) were screened, and an immunochromatographic strip (ICS) test for rapid and specific detection of cucumber green mottle mosaic virus (CGMMV) was developed. The coat protein of CGMMV was heterologously expressed as an immunogen, and specific capture mAb 2C9 and the detection mAb 4D4 were screened by an uncompetitive immunoassay. The test and control lines on the nitrocellulose membrane were coated with the purified 2C9 and a goat anti-mouse IgG, respectively, and a nanogold probe combined with 4D4 was applied to the conjugate pad. Using these mAbs, a rapid and sensitive ICS was developed. Within the sandwich mode of 2C9-CGMMV-4D4, the test line showed a corresponding positive relationship with CGMMV in infected samples. The ICS test had a detection limit of 1:5000 (w/v) for CGMMV in samples and was specific for CGMMV, with no observed cross-reaction with TMV or CMV.

Development of a colloidal gold immunochromatographic test strip for the rapid detection of iprodione

Iprodione is a dicarboximide fungicide that is widely used in agriculture around the world. A reliable and rapid detection method is needed for the on-site monitoring of iprodione residues in a variety of agricultural products. Herein, a colloidal gold immunochromatographic test strip was developed based on a selected coating antigen and a specific monoclonal antibody against iprodione. The particle size of colloidal gold, the preparation technique of the conjugate pad, the composition of the loading buffer, and the extraction solvent were comprehensively optimized for the test strip. A cut-off value of 0.9 mg kg^-1 (50 ng mL^-1) and a visual limit of detection of 0.09 mg kg^-1 (5 ng mL^-1) were achieved in a complex matrix of tobacco. No cross-reactivity was observed for iprodione metabolite and four other widely used pesticides during tobacco growth. Furthermore, the developed colloidal gold immunochromatographic test strip was applied to determine iprodione residues in tobacco samples, and the obtained results were in good agreement with those obtained by liquid chromatography tandem mass spectrometry. Additionally, the test strip was found to be stable afterlong-term storage at 37 °C for two months. The developed colloidal gold immunochromatographic test strip showed excellent accuracy, sensitivity, specificity, and stability, therefore, it is suitable for the rapid detection of iprodione residues in complex matrices.

An Overview for the Nanoparticles-Based Quantitative Lateral Flow Assay

The development of the lateral flow assay (LFA) has received much attention in both academia and industry because of their broad applications to food safety, environmental monitoring, clinical diagnosis, and so forth. The user friendliness, low cost, and easy operation are the most attractive advantages of the LFA. In recent years, quantitative detection has become another focus of LFA development. Here, the most recent studies of quantitative LFAs are reviewed. First, the principles and corresponding formats of quantitative LFAs are introduced. In the biomaterial and nanomaterial sections, the detection, capture, and signal amplification biomolecules and the optical, fluorescent, luminescent, and magnetic labels used in LFAs are described. The invention of dedicated strip readers has drawn further interest in exploiting the better performance of LFAs. Therefore, next, the development of dedicated reader devices is described and the usefulness and specifications of these devices for LFAs are discussed. Finally, the applications of LFAs in the detection of metal ions, biotoxins, pathogenic microorganisms, veterinary drugs, and pesticides in the fields of food safety and environmental health and the detection of nucleic acids, biomarkers, and viruses in clinical analyses are summarized.

Highly sensitive fluorescent sensing platform for imidacloprid and thiamethoxam by aggregation-induced emission of the Zr(Ⅳ) metal - organic framework

A novel luminescent UiO-66-NH₂ (UN) demonstrated great potentials to sense imidacloprid (IM) and thiamethoxam (TH) pesticides with high sensitivity and desirable selectivity. The UN exhibits superb luminescence emission properties, which have been found to enhance the aggregation-induced emission (AIE) of IM and TH. The enhanced AIE of IM and TH on UN has been applied for the sensitive sensing of IM and TH, and a limit of detection (LOD) of IM was estimated to be 5.57 μg/L. LOD of TH was found to be 0.98 μg/L, respectively. Interestingly, the other neonicotinoid pesticides showed a low interference response in recognition of IM and TH. More importantly, we have further demonstrated that the UN are successfully used to sense IM and TH in real samples of fruit juice with a high recovery of 85-116%, and relative standard deviation (RSD) were from 3.42% to 16.07%.