Blocking Oxidase-Mimicking Activity-Driven Label-Free Photothermal and Colorimetric Synergistic Sensing for Intelligent Onsite Detection of Tetracycline Residues in Milk

Considering the potential misuse of antibiotics to improve the yield and economic benefits in the production of animal-derived foods such as milk, the development of a simple, label-free, precise, reliable, low-cost, and onsite assay for antibiotic residues is highly desirable to ensure food safety. In this scenario, we here proposed a hybrid oxidase-mimicking nanozyme of the Ru@g-C3N4 nanosheet that combines with 3,3′,5,5′-tetramethylbenzidine (TMB) to develop a blocking oxidase-mimicking activity-driven photothermal and colorimetric synergistic sensing platform for intelligent onsite detection of tetracycline antibiotics (TCs). In the absence of TCs, the prominent oxidase-mimicking activity of Ru@g-C3N4 rapidly catalyzed colorless TMB to dark-blue oxTMB, accompanied by the appearance of an obvious absorbance enhancement at 655 nm and a remarkable photothermal signal upon 660 nm laser irradiation. Conversely, the remaining TCs effectively blocked this chromogenic reaction because of the π–π stacking of its tetraphenyl skeleton with the Ru@g-C3N4 nanozyme to block the affinity of TMB to the catalytic active site inside Ru@g-C3N4. Based on this, a TCs residual level-dependent photothermal and colorimetric signal synergistic decrease sensing platform was developed with the assistance of a 660 nm laser-assisted hand-held thermal imager and a Color Picker APP-inbuilt smartphone, which demonstrated the intelligent onsite label-free, reliable, and precise detection of TCs in real milk samples with acceptable results. Notably, this oxidase-mimicking nanozyme-based dual-mode sensing platform provided a built-in cross-reference correction to improve not only the accuracy but also the reliability for TC detection in milk, which showed a vast promise in the further development of commercial point-of-care testing to achieve early warning of antibiotic residues to ensure the quality and safety of animal-derived foodstuffs.