Chiral Carbon Quantum Dots Encapsulated in ZIF-8 Nanoparticles for Turn-On Recognition of Chiral Folic Acid and Nitrofurazone and Applications as Fluorescent Inks

Metal–organic frameworks (MOFs) are a kind of nanoporous coordination materials, which have the advantages of high crystallinity and tunable functionalization. Carbon dots (CDs) are zero-dimensional luminescent carbon nanomaterials, which combine the advantages of small organic molecules such as fluorophores and conventional semiconductors such as inorganic quantum dots. Chiral quantum dots are appealing for detection of chiral substances due to their unique chirality. In this work, chiral CDs can be loaded into zeolitic imidazolate framework-8 (ZIF-8) via an in situ encapsulation method, forming the chiral composite hybrid material CCQDs/ZIF-8 (1). The framework structure and luminescent property of 1 can be maintained after being soaked in water and ethanol for 24 h as confirmed by PXRD characterization. A luminescent experiment demonstrated that 1 can be utilized as a highly sensitive and selective "turn-on" fluorescent probe of d-folic acid (KBH 9.82 × 104 M–1 and detection limit 0.31 μM) and l-folic acid (KBH 2.99 × 104 M–1 and detection limit 4.36 μM). 1 also shows good cycling detection performance for d-folic acid (94.96%) and l-folic acid (93.69%). Enantioselective identification between d-folic acid and l-folic acid (KD/KL = 3.28) can be carried out. Furthermore, simultaneously, 1 can be used as an efficient turn-on fluorescence probe to detect the antibiotic nitrofurazone (NFZ; KBH 3.29 × 104 M–1 and detection limit 3.06 μM). Further, 1 can be utilized to detect folic acid and NFZ in real samples. The results demonstrated that 1 can be used as a highly efficient turn-on detection platform for folic acid and NFZ. Further, 1 with these targeted objects can be successfully applied as a fluorescent ink; a mixed-matrix membrane based on 1 has been prepared. The detection mechanism of composite material 1 for recognition of folic acid and NFZ is also investigated and discussed.