The HEK cell line was cultured and transferred into 96 nontransparent microplates (up to 10K/well) for its attachment and stabilization. After stabilization, 0.1X total volume (with cell medium) of the OA nanozyme (concentration varies) was added. The plates were incubated at 37°C for up to 24 hours. After incubation, the medium was removed, and the reagent (from the cell viability test kit) was put and incubated on the plate at room temperature for up to 20 minutes.