A molecularly imprinted ratio fluorescence sensor based on metal-enhanced fluorescence of core-shell structure CaF2-silver nanoparticle for visual detection of dicamba.

Although fluorescence analysis methods are widely used in pesticide residue detection, improving their sensitivity and selectivity remains a challenge. This paper presents a novel ratio fluorescence sensor based on the molecular imprinting polymers (MIPs) and metal-enhanced fluorescence for visual detection of dicamba (DIC). Calcium fluoride (CaF₂) quantum dots (QDs) were immobilized on the surface of Ag@MIPs, resulting in a blue fluorescence response signal (Ag@MIPs-CaF₂). The MIPs shell, which possesses a specific recognition capability, serves as an isolation layer to adjust the distance between Ag nanoparticles and CaF₂ QDs for enhancing the fluorescence of CaF₂ QDs by up to 7.1 times under optimal conditions. In the presence of DIC, the blue fluorescence was selectively quenched, while the reference signal red fluorescence from cadmium telluride QDs coated with silicon dioxide (CdTe@SiO₂) remained relatively stable, resulting in a color change from blue to red. The sensor had a detection limit of 0.16 μM for DIC in the range of 1.0 to 50.0 μM, recovery rates of 85.4 to 103.5% for actual samples, and an imprinting factor of 3.28. The 3D finite-difference time-domain simulation revealed that the fluorescence enhancement was due to the local electric field amplification. Therefore, the developed sensing system in this work offers a broad application prospect for visual detection of DIC in food samples.