Encapsulating Cu NCs with aggregation-induced emission into metal–organic framework ZIF-8 as a novel fluorescent nanoprobe for the highly sensitive detection of felodipine

Fluorescent metal-organic framework nanocomposites (f-MOFs) have been gaining increasing attention in the fields of chemosensors and biosensors due to their unique signal amplification mechanisms and improved selectivity. However, most f-MOFs are constructed by encapsulating fluorescent labelling agents into frameworks <i>via</i> host-guest interactions. The notorious aggregation-caused quenching effect of these fluorescent labelling agents often leads to a decreased fluorescent quantum yield in f-MOFs. Herein, a novel fluorescent nanocomposite, Cu NCs@ZIF-8, was designed and prepared by encapsulating copper nanoclusters (Cu NCs) with aggregation-induced emission (AIE) effects into zeolitic imidazolate framework ZIF-8 through electrostatic attraction. Owing to the AIE effect of Cu NCs and the spatial confinement of ZIF-8, the intramolecular motion of surface ligand hydrolipidic acid (DHLA) in Cu NCs was restricted, resulting in the formation of a highly emissive nanocomposite, Cu NCs@ZIF-8. Intriguingly, the UV-Vis absorption spectrum of felodipine overlaps with the excitation spectrum of Cu NCs@ZIF-8. Therefore, a novel fluorescent nanoprobe based on Cu NCs@ZIF-8 was developed for the highly sensitive detection of felodipine <i>via</i> the inner-filtration effect mechanism. Under optimal detection conditions, the linear response range of Cu NCs@ZIF-8 for felodipine was found to be 1-25 μM, with a detection of limit of 0.09 μM. While determining the labelling-amount percentage in commercially available felodipine tablets, the experimental results validated that the proposed Cu NCs@ZIF-8 nanoprobe exhibits good selectivity and excellent accuracy. This expands the potential applications of fluorescent metal-organic frameworks encapsulated with metal nanoclusters exhibiting AIE properties, positioning them as fluorescent nanoprobes for pharmaceutical quality control.