Multi-mode sensing platform for gallic acid determination based on the peroxidase-like activity of magnetic Fe3O4@Co/Ni/Al-LDH nanospheres

The determination of gallic acid (GA), one of the most prevalent antioxidants in various plants, provides information for food nutrition evaluation. A novel colorimetric, fluorescent, and smartphone multi-mode GA sensing platform based on Fe3O4@Co/Ni/Al-layered double hydroxide (LDH) nanospheres was designed in this study. The core-shell magnetic Fe3O4@Co/Ni/Al-LDH nanospheres were synthesized through a simple coprecipitation approach. They showed dominate peroxidase-like activities capable of oxidizing 3,3 ',5,5 '-tetramethylbenzidine (TMB) into a blue colored oxidation oxTMB. Meanwhile, the generated oxTMB could quench the fluorescence of neutral red via the inner filter effect. GA acted as an inhibitor to prevent the oxidation of TMB to oxTMB and restoring the fluorescence of neutral red. Under optimized conditions, the linear ranges were 0.5-120 mu mol/L with detection limits of 0.137-0.415 mu mol/L. Besides, the sensor exhibited good selectivity toward GA over various interferents. Moreover, it was successfully utilized to analyze GA in tea beverages with ideal recoveries of 92.8-105%, demonstrating good reliability and stability in practical applications. This study provided Fe3O4@Co/Ni/Al-LDH nanospheres as candidate nanozymes for the construction of biosensors. The multi-mode self-checking function and the "turn on" fluorescent sensing strategy offered this sensor superior anti-interference ability, and opens up a new strategy for the determination of antioxidants in foods.