A fluorescent magnetic nanosensor for imidacloprid based on the incorporation of polymer dots and Fe3 O4 nanoparticles into the covalent organic framework.

A magnetic nanoprobe was designed for imidacloprid by encapsulating nonconjugated polymer dots (NCPDs) and Fe3 O4 nanoparticles in the covalent organic framework (COF). The fluorescence intensity of the COF-based nanocomposite is markedly suppressed by imidacloprid. As the absorption spectrum of imidacloprid was close to the band-gap of the NCPDs, and due to the presence of a nitro group (as an electron acceptor), the electrons can be easily transferred from the conduction band of NCPDs to the LUMO of imidacloprid, so fluorescence quenching was more likely to have been caused by the electron transfer process. The COF-based nanosensor was used for the determination of imidacloprid in the linear range 1.3-130 nM with a detection limit of 1.2 nM. The high sensitivity of the 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 Fe3 O4 nanoparticles, which leads to further enrichment of imidacloprid. The magnetic nature of the nanocomposite enables the preconcentration and easy separation of the analyte, and so reduces matrix interference and lowers the detection limits. The practicality of this nanoprobe was confirmed by quantification of imidacloprid in the wastewater and fruit juice samples.

Eco-friendly nonconjugated polymer dots for chemiluminometric determination of 4-nitrophenol.

Polymer dots (PDs) are a new family of quantum dots for which their behavior and potential applications have not yet been completely explored. In this study, nonconjugated PDs were synthesized using a simple pyrolysis method and used for the chemiluminescence (CL) assay of 4-nitrophenol (4-NP). PDs increased the CL signal of the Ce(IV)-Na2 SO3 reaction 39-fold. Using the CL spectrum, it was concluded that the emission at 434 nm was generated by excited PDs (PDs*), which are produced by energy transfer from SO2 * to PDs. Our experiments showed that 4-NP enhanced the CL signal of the Ce(IV)-Na2 SO3 -PDs reaction. The mechanism of this effect was explored by obtaining CL, ultraviolet-visible, and Fourier transform infrared spectra. Due to the high sensitivity and selectivity of the CL system for 4-NP, a probe was designed to determine 4-NP in the linear range 1.0-500 nmol/L with a detection limit of 0.33 nmol/L. Different spiked real samples were successfully analyzed using this probe.

A new enhanced chemiluminescence reaction based on polymer dots for the determination of metronidazole.

Polymer dots (PDs) with non-conjugated functional groups are attracting nanomaterials due to their ease of synthesis, the biocompatibility of precursors, and low toxicity. In this work, PDs with non-conjugated groups were synthesized with a simple and straightforward method by Schiff base reaction. Then their possible application in the chemiluminescence (CL) reactions was explored. Results were shown that PDs increased the CL intensity of the NaIO4-fluorescein system about 15 times. Regarding the CL mechanism, we proved that the emitting species is fluorescein, which can be excited by the energy transfer from the excited-state PDs. It was observed that CL emission is promoted by the interaction of metronidazole (MND) with the PDs. Therefore, we designed a novel and sensitive assay for MND based on its enhancing effect on NaIO4-fluorescein-PDs CL system. The introduced assay showed a linear response in the range of 5.0-300 nM with a detection limit of 1.5 nM. The method was used for the determination of MND in spiked plasma samples.