Magnetic Cu/Fe3O4@FeOOH with intrinsic HRP-like activity at nearly neutral pH for one-step biosensing

The convenience of colorimetric sensors is useful for practical applications. In this work, we constructed a novel colorimetric sensor with magnetic separation ability that can be operated in nearly neutral conditions and achieve one-step detection of metabolites. Magnetic Cu doped Fe 3 O 4 @FeOOH magnetic nanocomposite (Cu/Fe 3 O 4 @FeOOH) with an oxygen vacancy was prepared by a one-step self-assembly hydrothermal method, and fully characterized by different methods. The oxygen vacancy generated by the incorporation of Cu 2+ cations into the Fe 3 O 4 @FeOOH structure was confirmed to be a vital reactive site for enhancing the catalytic activity, which opens up a new way of designing highly efficient enzyme mimics. Benefiting from its inherent horseradish-peroxidase-like activity, a simple and selective enzyme-based colorimetric sensor was developed for one-step detection of H 2 O 2 and cholesterol, and 3,3′,5,5′-tetramethylbenzidine was catalyzed by H 2 O 2 to generate a colored product of oxidized 3,3′,5,5′-tetramethylbenzidine for signaling. H 2 O 2 and cholesterol can be linearly detected in the same range from 0.01 to 0.4 mmol L -1 with detection limits of 0.0075 mmol L -1 and 0.0082 mmol L -1 , respectively. The proposed colorimetric sensor has satisfactory reusability, accuracy, and practicability in human serum samples, indicating its potential application for the detection of different metabolites in the fields of life science and analytical science. Graphical abstract