(A) Representative EPR spectra of the O2•− sensitive CMH spin probe in cell-free samples treated with vehicle, native CuZnSOD protein, reducible cl-nanozyme, or non-reducible cl-nanozyme. Superoxide was generated in these cell-free samples by hypoxanthine and xanthine oxidase. (a.u. – arbitrary units). (B) Summary EPR spectroscopy data showing CMH spectra amplitude, which is directly proportional to the amount of O2•− in the sample, in hypoxanthine/xanthine oxidase-containing samples treated with vehicle, native CuZnSOD protein, non-crosslinked nanozyme, reducible cl-nanozyme, or non-reducible cl-nanozyme (n = 4–5 per group). Data represent mean ± SEM. * P < 0.05 vs. vehicle.