Regulating the redox and non-redox enzyme-mimicking activities of Ce-UiO-66-NO2 nanozyme for dual-mode sensing of phosphate

Nanozymes with multi-enzyme mimicking activities have received a great deal of attention, which can mimic peroxidase, oxidase, superoxide dismutase, catalase, and alkaline phosphatase, etc. However, the current research focuses on regulating the multi-enzyme-like activity of redox types. Regulating the catalytic activity of different types of nanozyme such as redox and non-redox types is still full of challenges. Here, Ce-UiO-66-NO2 with hydrolase-like activity and oxidase-like activity was taken as the model to regulate its dual enzyme-like activities. Interestingly, a distinct response in oxidase-like and hydrolase-like activities of Ce-UiO-66-NO2 was observed towards the addition of phosphate (PO43-). When PO43- is present, the oxidase mimicking activity of Ce-UiO-66-NO2 was enhanced and the hydrolase mimicking activity was inhibited. With X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, X-ray diffraction and zeta potential characterizations, the regulatory mechanism was recognized as the coordinated impact of the reactive oxygen species, electrostatic adsorption and competitive inhibition. As a proof of concept, a colorimetric/fluorometric dual-mode sensing method for detecting PO43- through regulating the dual enzyme mimicking activities of Ce-UiO-66-NO2 was constructed. PO43- can be quantitated with 3,3',5,5'-tetramethylbenzidine (TMB) and 4-methylumbelliferyl phosphate (4-MUP) as substrates for colorimetric and fluorescent sensing, respectively. This study will deepen the understanding of nanozymes with multi-enzyme mimicking activities and accelerate the development of efficient sensing.