Defective Fe/Co-MOF with abundant oxygen vacancies as an efficient oxidase mimic for colourimetric and sensitive determination of tetracycline

The abuse of tetracycline (TC) has led to serious threats to human health and the environment. Therefore, the rapid and sensitive detection of tetracycline is of particular importance. Herein, we successfully synthesised a bimetallic nanozyme D-Fe/Co-MOF with oxidase activity and established a colourimetric sensor. The complex of Fe2+ in D-Fe/Co-MOF and TC can release hydroxyl radicals ((OH)-O-center dot) and promote the oxidation of TMB. As a result, the colour of the detection system significantly changes, enabling the sensitive colourimetric detection of TC. Compared with the existing Fe/Co-MOF sensor, D-Fe/Co-MOF can effectively reduce the detection error caused by hydrogen peroxide decomposition, improving the accuracy of TC detection. Under the optimal conditions, the absorbance at 652 nm showed a good linear relationship with TC concentration in the range of 0.35-220 mu g mL-1. The detection limit was as low as 0.0719 mu g mL-1, considerably lower than the national safety standard. The proposed colourimetric sensor was also successfully used for the detection of TC in actual milk samples, and the results were in good agreement with those obtained via liquid chromatography. The proposed strategy for the detection of TC in food is expected to contribute to ensuring food safety and human health. A colourimetric sensor was established based on the bimetallic nanozyme D-Fe/Co-MOF. With the addition of TC, the colour of the detection system changed from blue to yellow. Based on this transformation, a colourimetric detection method for TC was proposed.