ABTS-Persulfate Reaction Protocol

We weighed out 194.1 mg of 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 68.6 mg of potassium persulfate, and dissolved them in ultrapure water (100 mL) to prepare a mixed solution with concentrations of 3.5 mmol/L for 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and 2.5 mmol/L for potassium persulfate. The reaction took place in the dark at 4 °C for 12 h. Prior to usage, we diluted the sample with ethanol and adjusted the solution to an absorbance of 1.0 at 750 nm on a Cary 60 UV-Vis Spectrophotometer (Agilent Technologies, Inc., Santa Clara, CA, USA).