Developing a Molecular Imprinting Sensor Based on Double-Layer Coating Structure for the Rapid and Sensitive Detection of Chlortetracycline in Milk

As a common food in the modern world, milk safety is becoming increasingly concerning, with a major issue being the presence of antibiotic residues. These residues can lead to problems such as drug resistance, immunosuppression, mutagenesis, teratogenesis, and carcinogenesis. In this study, a sensor for the rapid and sensitive detection of CT residues in milk was developed for the first time by re-coating magnetic covalent organic frameworks (COFs) and molecularly imprinted polymer (MIP) on a gold electrode. CTs served as the template molecule, while EDTA and NHS were used as cross-linkers. Poly(o-phenylenediamine) was utilized as the MIP layer, and 95% methyl alcohol was used as the eluent. The surface of the gold electrode was successively coated with a layer of COFs and a layer of MIP. The advantage of this coating method was that it enhanced the sensor’s storage time and improved its performance in detecting CT residues. The electrochemical signal was amplified by Fe₃O₄, while the electrochemical signal was simultaneously controlled by the elution and rebinding of CTs in the MIP. Based on these principles, the detection was established. Under optimal detection conditions, the prepared sensor achieved a sensitivity of 0.3 × 10⁻¹² mol/L. The sensor exhibited good selectivity, allowing it to differentiate the target molecule from nine other common molecules, such as chloramphenicol, streptomycin, and penicillin. Additionally, the sensor displayed excellent reproducibility and ideal stability, remaining stable for 5 weeks with only a 0.2% decrease in signal. Furthermore, the detection of real milk samples showed that the sensor performed effectively, demonstrating its potential for detecting residual CTs in milk.