S-Modified MOF Nanozyme Cascade System with Multi-Enzyme Activity for Dual-Mode Antibiotic Assay

The judicious utilization of antibiotics has established a robust bulwark for human health. However, their improper usage has engendered deleterious ramifications on the environment, underscoring the imperative for developing efficacious and cost-effective detection and degradation platforms. This study presents a sulfur-modified iron–cobalt bimetallic single-atom nitrogen-doped carbon catalyst (S-FeCo-NC) with a noncopper active center. In contrast to conventional laccase, which utilizes copper as its active center, the S-FeCo-NC catalyst exhibits multiple enzyme activities, including laccase-like, peroxidase-like, and catalase-like functions, with iron and cobalt serving as the active centers. As a proof of concept, the combined laccase-like and catalase-like functions of S-FeCo-NC were used as independent signal outputs, while a multienzyme cascade dual-mode assay system was designed for the rapid detection of tetracycline (TC) in combination with peroxidase-like enzymes. In this system, oxygen directly participated in the catalytic process of laccase-like as an electron acceptor, while catalase-like peroxidase efficiently catalyzed the production of O₂ from H₂O₂. The elevated concentration of O₂ offered a unique advantage for the increased catalytic activity of the laccase-like enzyme, which outputs visually resolved colorimetric signals using stable 4-aminopyridine with oxidized TC. Furthermore, the peroxidase-like activity of S-FeCo-NC catalyzed the generation of OH radicals with strong oxidative properties, and these radicals carried out effective oxidative decomposition of TC. The signal output of the response of the catalytic process was performed using differential pulse cyclic voltammetry, which further improved the sensitivity and accuracy of the detection. The experimental findings demonstrate that the detection system exhibits a favorable response signal to TC within the range of 0.005–500 μM, with its detection range reaching 0.5–500 and 0.005–1.00 μM, respectively, and the detection limit is as low as 0.22 μM and 1.68 nM, respectively. This cascade dual-mode detection system, based on multienzyme activity, has been shown to significantly enhance the catalytic activity of laccase, while also demonstrating stability in a lower detection range. This suggests that it may offer a novel approach for the sensitive detection and degradation of environmental pollutants.