2.5.2. ABTS Radical Cation Decolonization Assay

The assay of ABTS radical cation scavenging ability was performed as described previously with some modification [28]. ABTS and potassium persulfate (K2S2O8) were dissolved in distilled water. A stock solution of ABTS•<sup>+</sup> was prepared by mixing 7.4 mM ABTS solution with 2.6 mM K2S2O8 solution. The mixture was incubated for 12 h in the dark to reach equilibrium. The ABTS•<sup>+</sup> stock solution was diluted with sodium phosphate buffer (pH 7.4) to obtain an optical density of 0.70 ± 0.02 at 734 nm. Then 1 mL of different concentrations of PSP, SeNPs, PSP-SeNPs, and Vc (0.01, 0.05, 0.1, 0.25, 0.5, 0.75, 1.0 mg/mL) was added to 4 mL of diluted ABTS•<sup>+</sup> solution. The mixture was vigorously blended and incubated at room temperature for 6 min in darkness. The absorbance was measured at 734 nm using a UV-vis spectrophotometer. The ability to scavenge ABTS•<sup>+</sup> was calculated by Equation (2).

$$\text{ABTS}^{\bullet+} \text{radical scanning ability} \left( \% \right) = \left( 1 - \frac{\text{A}\_{\text{d}} - \text{A}\_{\text{e}}}{\text{A}\_{\text{f}}} \right) \times 100 \tag{2}$$

where Ad is the absorbance of the sample mixed with the ABTS•<sup>+</sup> solution, Ae is the absorbance of the sample in the absence of the ABTS•<sup>+</sup> solution, Af is the absorbance of the ABTS•<sup>+</sup> solution without the sample.
