The same electrochemical technique was employed to measure ROS levels in HL-1 cardiomyocytes (control and DOX-treated cells) as well as in heart tissue obtained from mice treated with DOX (20 mg/kg) or control. In both in vitro cell-line studies and in vivo animal experiments, 80 µL of cells or tissue resuspended in Dulbecco's PBS solution was applied to the working area of the rGO-Co₃O₄-Pt/SPEs.