Preparation of Core-Shell Rare Earth-Doped Upconversion Nanomaterials and Simultaneous Detection of Two Pesticides in Food

Abstract

Under the excitation of a 980 nm excitation light, the fluorescence signals of the synthesized core-shell NaYF4:Yb@NaYF4:Ho and monolayer NaYF4:Yb,Tm upconversion nanoparticles (UCNPs) were simultaneously detected at 656 and 696 nm, respectively. The two upconversion materials were coupled with anti-clothianidin and anti-imidacloprid monoclonal antibodies by the glutaraldehyde cross-linking method as signal probes. Imidacloprid (IMI) and clothianidin (CLO) could compete with antigen-conjugated amino Fe3O4 magnetic nanomaterials for binding to signaling probes, thus establishing a rapid and sensitive fluorescent immunoassay for the simultaneous detection of IMI and CLO. Under optimal conditions, the limits of detection (LOD, IC10) and sensitivity (IC50) of IMI and CLO were (0.032, 0.028) and (4.7, 2.1) ng/mL, respectively, and the linear assay ranges were at 0.032–285.75 ng/mL and 0.028–200 ng/mL, respectively. Immunoassay did not cross-react significantly with other analogs. In fruits and vegetables such as apples, oranges, peaches, cucumbers, tomatoes and peppers, the mean recoveries of IMI and CLO ranged from 83.33% to 115.02% with relative standard deviations (RSDs) of 1.9% to 9.2% and 1.2% to 9.0%, respectively. Furthermore, the results of the immunoassay correlate well with the high-performance liquid chromatography method used to detect the actual samples.