Construction of a Nanozyme Sensor Based on α-Fe ₂ O ₃ /ZIF-67 Composite for Sensitive Colorimetric Detection of H ₂ S and Cu ²⁺

An increase in copper ion content and the simultaneous decrease in hydrogen sulfide (H 2 S) are the important factors causing Alzheimer’s disease. Therefore, it is necessary to develop a simultaneous, sensitive, and rapid method for detecting sulfide ions (S 2– ) and copper ion (Cu 2+ ) in biological systems. In this study, a colorimetric method for detecting sulfide ions using a composite of ferric α-iron oxide and zeolitic imidazolate framework-67, namely α-Fe 2 O 3 /ZIF-67, was developed. α-Fe 2 O 3 /ZIF-67 with peroxidase (POD)-like activity was synthesized by hydrothermal methods using the α-Fe 2 O 3 –ZIF-67 composite. In the presence of H 2 O 2, this prepared nanozyme catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine to generate a blue oxidation product. In the presence of H 2 S, the active sites of α-Fe 2 O 3 /ZIF-67 combined with it, and the POD-like activity was inhibited, resulting in the disappearance of the blue color. This method achieved the colorimetric detection of S 2– at 652 nm with a linear range of 0.4–128 μM and a detection limit of 0.27 μM. Furthermore, Cu 2+ were simultaneously detected by colorimetry due to the restoration of the nanozyme via strong bonding of Cu 2+ and S 2– . This platform has been successfully applied to the detection of S 2– in human serum.