Cancer-Cell Imaging Using Copper-Doped Zeolite Imidazole Framework-8 Nanocrystals Exhibiting Oxidative Catalytic Activity

Copper-doped zeolite imidazole framework-8 (Cu/ZIF-8) was prepared and its peroxidase-like oxidative catalytic activity was examined with a demonstration of its applicability for cancer-cell imaging. Through simple solution chemistry at room temperature, Cu/ZIF-8 nanocrystals were produced that catalytically oxidized an organic substrate of o-phenylenediamine in the presence of H₂O₂. In a similar manner to peroxidase, the Cu/ZIF-8 nanocrystals oxidized the substrate through a ping-pong mechanism with an activation energy of 59.2 kJ mol⁻¹. The doped Cu atoms functioned as active sites in which the active Cu intermediates were expected to be generated during the catalysis, whereas the undoped ZIF-8 did not show any oxidative activity. Cu/ZIF-8 nanocrystals exhibited low cell toxicity and displayed catalytic activity through interaction with H₂O₂ among various reactive oxygen species in a cancer cell. This oxidative activity in vitro allowed cancer-cell imaging by exploiting the photoluminescence emitted from the oxidized product of o-phenylenediamine, which was insignificant in the absence of the Cu/ZIF-8 nanocrystals. The results of this study suggest that the Cu/ZIF-8 nanocrystal is a promising catalyst for the analysis of the microbiological systems.