L methionine

The O₂·⁻ depletion activity of Cu NZs@PLGA nanofibers was investigated via the nitroblue tetrazolium (NBT) chromogenic method. Cu NZs@PLGA nanofibers were immersed in Tris-HCl buffer (10 mM, pH 7.4) (Biosharp, China) with a final Cu NZs concentration of 150 ng mL⁻¹. After 0, 2, 6, or 12 h preincubation, the working solution containing 6.5 mM l-methionine (C11385354, Macklin, China), 37.5 μM NBT (C11167116, Macklin, China), and 10 μM riboflavin (C11507808, Macklin, China) was homogeneously mixed with the pre-treated Tris-HCl solutions, respectively, and irradiated using a SCIENTZ03-II UV radiation instrument (Scientz, China) with a wavelength of 254 nm (60 W, 150 mm) for 3 min at RT. UV irradiation resulted in the generation of O₂·⁻ from riboflavin and l-methionine, which further converted NBT to blue formazan. After illumination, the absorbances of the mixtures were measured by a UV–Vis spectrophotometer at a wavelength of 560 nm. The clearance rate of O₂·⁻ was calculated according to the same formula of H₂O₂ clearance rate.