Co3O4/CuO hollow nanocage hybrids with high oxidase-like activity for biosensing of dopamine.

Here, we report the synthesis, characterization, and oxidase-like activity of Co3O4/CuO hollow nanocage (HNC) nanocomposites. The Co3O4/CuO HNCs were successfully prepared by hydrothermal treatment of ZIF-67 in copper nitrate solution, followed by carbonization in air. The obtained nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Co3O4/CuO HNCs possess enhanced oxidase-like activity compared with pure Co3O4 and CuO, and they can catalytically oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) substrate in the absence of H2O2 to produce an intense blue product. Reactive oxygen species (ROS) measurements indicate that 1O2 and O2- radicals are the major ROS in catalytic oxidation of TMB by dissolved oxygen in the TMB-Co3O4/CuO HNC system. We then developed a simple, sensitive, visual, and colorimetric biosensing method for dopamine (DA) based on its inhibiting effect on TMB oxidation. The proposed method allows for DA detection with a limit of detection of 0.027 μM and a dynamic range of 0.05-8 μM. This new colorimetric method was successfully used to detect DA in biological samples. The present work demonstrates a simple strategy to fabricate an efficient oxidase mimic with potential applications in bioanalysis and clinical diagnosis.