A fluorescent magnetic nanosensor for imidacloprid based on the incorporation of polymer dots and Fe 3 O 4 nanoparticles into the covalent organic framework.

A magnetic nanoprobe was designed for imidacloprid by encapsulating nonconjugated polymer dots (NCPDs) and Fe 3 O 4 nanoparticles in the covalent organic framework (COF). The fluorescence intensity of the COF-based nanocomposite is remarkably suppressed by imidacloprid. Since, the absorption spectrum of imidacloprid was close to the band gap of the NCPDs and due to the presence of nitro group (as an electron acceptor), the electrons can be easily transferred from the conduction band of NCPDs to the LUMO of imidacloprid, so the fluorescence quenching is more likely caused by the electron transfer process. The COF-based nanosensor was used for the determination of imidacloprid in the linear range of 1.3-130 nM with a detection limit of 1.2 nM. The high sensitivity of nanoprobe for imidacloprid is due to the combination of COF benefits (accumulation of the imidacloprid into the COF cavities) and the high adsorption ability of the Fe 3 O 4 nanoparticles, which leads to further enrichment of imidacloprid. Magnetic nature of the nanocomposite enables the preconcentration and easy separation of analyte, and so reduces the matrix interference and lowers the detection limits. The practicality of this nanoprobe was confirmed by the quantification of imidacloprid in the wastewater and fruit juice samples.