Competitive immunoassay for simultaneous detection of imidacloprid and thiacloprid by upconversion nanoparticles and magnetic nanoparticles
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A rapid and sensitive immunoassay for the simultaneous detection of imidacloprid and thiacloprid was developed by using magnetic nanoparticles (MNPs) and upconversion nanoparticles (UCNPs). The UCNPs of NaYF4:Yb, Er and NaYF4:Yb, Tm were synthesized and conjugated with anti-imidacloprid monoclonal antibody (mAb) and anti-thiacloprid mAb as signal labels, while the MNPs were conjugated with antigens of thiacloprid and imidacloprid as separation elements. The fluorescence intensities of Yb/Er- and Yb/Tm-doped UCNPs were detected simultaneously in 544 nm and 477 nm under the excitation of NIR light (980 nm). The amounts of mAb-conjugated UCNPs that were separated by antigen-conjugated MNPs were determined based on competitive immunoassays. Under the optimal conditions, the 50% inhibiting concentration (IC50) and limit of detection (LOD, IC10) were 5.80 and 0.32 ng/mL for imidacloprid and 6.45 and 0.61 ng/mL for thiacloprid, respectively. The immunoassay exhibited negligible cross-reactivity with analogs of imidacloprid and thiacloprid except imidaclothiz (86.2%). The average recoveries of imidacloprid and thiacloprid in environmental and agricultural samples, including paddy water, soil, pears, oranges, cucumbers, and wheat, ranged from 78.4 to 105.9% with relative standard deviations (RSDs) of 2.1–11.9% for imidacloprid and ranged from 82.5 to 102.3% with RSDs of 1.0–16.5% for thiacloprid. In addition, the results of the immunoassay correlated well with high-performance liquid chromatography for the detection of the authentic samples.
KeywordsImidacloprid Thiacloprid Magnetic nanoparticles (MNPs) Upconversion nanoparticles (UCNPs) Simultaneous detection
This work was supported by the National Key Research and Development Program of China (2017YFF0210200), the Fundamental Research Funds for the Central Universities (KYZ201618), and the National Natural Science Foundation of China (31772194).
Compliance with ethical standards
The authors declare that they have no competing interests.