Innovative on-site colorimetric assay of tetracyclines by smartphones in waters and milks based on a synergistic co-catalyst FeMoO4@Fe7S8 with strong interactions and complexation

Abstract

Tetracyclines are widely used in livestock breeding, while their rapid/on-site detection still remains a technical challenge. Herein, we designed an innovative idea to improve Fe²⁺/Fe³⁺ conversion efficiency using Mo-based nanomaterials and synergistic coupling of heterostructure. FeMoO₄ was adopted as a co-catalyst to construct FeMoO₄@Fe₇S₈ nanoplatelets (NPs) with the higher peroxidase-like (POD) activity in the chromogenic system. The coloring development catalyzed by FeMoO₄@Fe₇S₈-1 NPs mainly involved the participation of h⁺ and ·OH, and its excellent POD activity resulted from heterostructure with abundant active sites and strong interactions between multi-valence Fe and low-valence Mo. FeMoO₄@Fe₇S₈-1 NPs tended to preferentially complex with C₄N–C_12aO and C₄N⁻ on the ring A of oxytetracycline. Tetracyclines caused the significant enhancement of the 654 nm absorption in the “FeMoO₄@Fe₇S₈-1 NPs + H₂O₂ + TMB” system, providing the linear response from 0.1 to 90 μM and low limit of detection (LOD) of 0.03 μM. To realize the rapid quantitation of TCs, a “thing identify” APP was pioneered along with an auxiliary imaging interferogram device. The smartphone-based colorimetric assay platform gave the linear response of 0.1–20 μM and LOD of 0.03 μM in water and milk samples, which were comparable with UV-vis analysis and HPLC-DAD detection. Overall, these findings offer a novel idea for convenient, rapid and on-site monitoring TCs in environmental and food media.