A Ratiometric Fluorescent Sensor for the Detection of Norfloxacin in Foods Based on ZIF-8 Core–Shell-Structured Molecularly Imprinted Encoded Microspheres

The development of fluorescent sensors with high sensitivity and fast response times is attracting the interest of more and more researchers. Herein, dual-emission ratiometric molecularly imprinted fluorescent encoded microspheres were fabricated and applied for the fast detection of norfloxacin. Core-shell-structured imprinted polymers with ZIF-8 as the supporting core were obtained first and two quantum dots with green and red emission provided the fluorescent signal. The introduction of the optical encoding technique greatly simplified the preparation process. After the addition of NOR, the green intensity at 525 nm remained constant and the fluorescent intensity at 625 nm decreased significantly because of the inner filter effect. Under the optimum detection conditions, a good linear correlation ranged from 5 μg L^-1 to 500 μg L^-1, and the spiked recoveries of the method were 89.76%-106.94%. The detection limit for chicken, pork, fish, and milk samples was established at 2 μg L^-1. More importantly, the established sensor provided a faster mass transfer rate, and the detection process took only 15 min, indicating great potential as an alternative for the fast detection of NOR in food samples.