Rare-earth (RE)-based nanoparticles have exhibited broad potential applications in the biomedical field owing to their unique magnetic and optical properties. But until now, there has been no reliable histochemical staining method developed for probing the distribution of RE-based nanoparticles in different organs and tissues, which is imperative for evaluating the targeting ability and safety profiles of RE-based nanoparticles used as the diagnostic probe and the therapeutic agent. Herein, the authors propose a novel and effective staining approach for identifying RE-based nanoprobes in tissues through unique chromogenic reactions between Chlorophosphonazo III and RE 3+ , which is independent of the element type. More importantly, a staining color analysis method based on the specific RGB range-selective integration of the stained images is developed for establishing a quantitative relationship between the optical density and RE 3+ concentration in the tissue slices.
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 NaYF 4 :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 (SC 50 ) and linear range (SC 10 − SC 90 ) 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. Graphical abstract 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.
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