Smartphone-Integrated Molecularly Imprinted Ratiometric Fluorescent Sensor for Selective and Visual Detection of Doxycycline in Lake Water and Foodstuff

Doxycycline (DOX) is extensively utilized as a broad-spectrum antibiotic in animals and aquaculture. However, excessive residues of DOX can endanger human health and ecosystems, adversely affecting sustainable development. A novel ratiometric fluorescent probe was designed for specific monitoring of DOX based on boron- and nitrogen-codoped carbon quantum dots encapsulated in metal–organic frameworks coupled with molecularly imprinted polymers (B,N-CQDs/ZIF-8@MIP). In the existence of DOX, the blue fluorescence was quenched owing to the inner filter effect, while the yellow-green fluorescence was enhanced due to the combination of DOX and Zn2+. Benefiting from the dual-signal strategy and the molecularly imprinted layer, the probe exhibited a wide linearity range (0.05–20 mg L–1), a favorable detection limit (LOD) of 14.21 ng mL–1, a fast response time (5 min), and exceptional selectivity. The validity of the probe was verified by detecting DOX in lake water and milk with desirable recoveries (90.16–97.18%). Moreover, a portable sensing device based on a smartphone-integrated B,N-CQDs/ZIF-8@MIP was utilized to achieve DOX visual sensing with a clear color change and an LOD of 44.98 ng mL–1. Therefore, the sensor with the advantages of portability, easy operation, and sensitivity showed tremendous application prospects for on-site detection in food and environmental safety.