Competitive immune-nanoplatforms with positive readout for the rapid detection of imidacloprid using gold nanoparticles.

Two high-sensitivity competitive immune-nanoplatforms based on the inner filter effect (IFE-IN) and magnetic separation (MS-IN) with a positive readout were developed to rapidly detect imidacloprid (IMI) using gold nanoparticles (AuNPs). For IFE-IN, IMI competes with AuNPs-labeled IMI antigens (IMI-BSA-AuNPs) to bind with anti-IMI monoclonal antibody (mAb)-conjugated NaYF4:Yb,Er upconversion nanoparticles, which changes the fluorescence signal at excitation/emission wavelength of 980/544 nm. For MS-IN, the immunocomplex of IMI-BSA-AuNPs and magnetic-nanoparticles-labeled mAb (mAb-MNPs) dissociates in the presence of IMI, and the optical density of IMI-BSA-AuNPs at 525 nm increases with the IMI concentration after magnetic separation. Under the optimal conditions, the IMI concentration producing a 50% saturation of the signal (SC50) and linear range (SC10- SC90) were found to be 4.30 ng mL-1 and 0.47 - 21.37 ng mL-1 for IFE-IN, while 1.21 ng mL-1 and 0.07 - 10.21 ng mL-1 for MS-IN, respectively. Both IFE-IN and MS-IN achieved excellent accuracy for the detection of IMI in different matrices. The quantities of IMI in apple samples detected by IFE-IN and MS-IN were consistent with the high-performance liquid chromatography results. For IFE-IN, analyte competes with AuNPs-labeled-antigen to bind with the mAb-conjugated-UCNPs, which changes the fluorescence signal at 544 nm. For MS-IN, the immunocomplex of AuNPs-labeled-antigen and mAb-conjugated-MNPs dissociates in the presence of analyte, and the optical density of AuNPs-labeled-antigen at 525 nm increases with increasing analyte concentration after separation.