Co3O4 hollow nanoparticles embedded in carbon nanoboxes as peroxidase-like nanozymes for the colorimetric determination of H2O2 and dopamine

Nanozymes are interesting alternatives to natural enzymes since they are highly stable and inexpensive. Here, we present a straightforward MOF-based etch, pyrolysis, and oxidation approach for fabricating an attractive hybrid structure comprised of extensively distributed ultrafine Co3O4 hollow particles embedded in carbon nanoboxes (denoted as HP-Co3O4@C NBs), which exhibit the catalytic property of peroxidase-like nanozyme. The ultrafine size and hollow structure of Co3O4 particles provide a large surface area and abundant catalytic sites of HP-Co3O4@C NBs. Mechanistic studies show that the production of reactive oxygen species (ROS) intermediates (•OH) through the decomposition of H2O2 endows the peroxidase-like activity of HP-Co3O4@C NBs. 3, 3′, 5, 5′-tetramethylbenzidine (TMB) transforms into a blue oxidation product (oxTMB) in the presence of H2O2 with the catalysis of HP-Co3O4@C NBs. In the existence of the reducing substance dopamine (DA), the oxidation reaction of TMB is inhibited, resulting in a marked bleaching of the blue colour. Based on these principles, we develop a colourimetric sensing platform for detecting DA with excellent sensitivity and stability. This study not only extends the application of Co-MOFs in the analytical field, but also achieves a simple, rapid (3 min), sensitive, and intuitive detection of H2O2 and dopamine, which is potentially promising for real-time monitoring of biological small molecules.