A fluorescent turn-off sensor based on polydopamine modified Mg-Al layered double hydroxide for the detection of thiram in apple and pear samples

A low-cost and environmentally friendly polydopamine modified layered double hydroxides (PDA/LDH) was prepared, and a novel fluorescent “turn-off” sensor was established for rapid detection of thiram. The material was characterized using the transmission electron microscope (TEM), Fourier transform-infrared (FT-IR), X-ray diffraction (XRD), X-ray photo-electronic spectroscopy (XPS) and other methods. The electrostatic interaction, hydrogen bonding and S-π interaction between PDA/LDH and thiram were mostly attributed to the sensing of thiram. Through the internal filter effect (IFE), the fluorescence of the PDA/LDH could be effectively quenched by thiram. The limit of detection (LOD) was determined to be 25 μg L⁻¹ under optimal conditions, while the concentration of thiram in the range of 50–50000 μg L⁻¹ exhibited a satisfactory relationship with the change in fluorescence intensity. Furthermore, the prepared probes were successfully applied on apple and pear samples, in which the recovery rate could reach 92.06–104.90 %. The synthesis of PDA/LDH was quite simple, and the detection of thiram could be accomplished right away when the sensor and thiram were combined. All the above results demonstrated the high potential of the established method in practical applications.