2.6. DPPH Radical-Scavenging Ability of Ser-PAMAM-Cys

The free radical-scavenging ability of Ser-PAMAM-Cys was evaluated by the DPPH method with a modification [18]. About 100 µL of 625 µM DPPH in ethanol was added 20 µL of 50 µM Ser-PAMAM-Cys and Cys (as the thiol concentrations in PBS) then incubated at room temperature for 60 min. Absorbances were measured at 540 nm in a microplate reader (PowerScan HT, BioTek Instruments Inc., Winooski, VT, USA).