Figure 2. Quantification of H₂O₂ produced in PBS(Ca²⁺/Mg²⁺) by He plasma.

(A) Absorption spectra between 250 and 400 nm of 1 mM Na₃VO₄ solutions in PBS(Ca²⁺/Mg²⁺) and incubated with increasing concentration of H₂O₂. (B) Correlation between the change in the optical density at 260 nm and 270 nm of 1 mM Na₃VO₄ solutions and the concentration of H₂O₂. The data are the mean ± sd of 12 independent experiments. The equations and correlation coefficients in black and red were derived from the linear regression of the values at 260 and 270 nm, respectively. (C) Absorption spectra between 250 and 400 nm of 1 mM Na₃VO₄ solutions in PBS(Ca²⁺/Mg²⁺) exposed to He gas or He plasma for 2 and 4 min. (D) Comparison between the absorption spectra of H₂O₂ solutions at 800 μM and 2 mM and the absorption spectra of plasma-activated PBS(Ca²⁺/Mg²⁺) after 2 and 4 min of treatment. The spectra are the average ± SD of 3 independent experiments. (E) Solutions of PBS(Ca²⁺/Mg²⁺) containing (direct treatment) or not (indirect treatment) 1 mM Na₃VO₄ were exposed to He plasma for 1, 2, 3, or 4 min. For indirect treatment, Na₃VO₄ was then added to plasma-treated PBS. The optical density of each solution was recorded at 260 and 270 nm, and the concentration of H₂O₂ determined using equations shown in panel B. The data are the mean ± SD of 12 independent experiments (t-test **p < 0.01). Insert: Solutions of PBS(Ca²⁺/Mg²⁺) were exposed to He plasma and were diluted 2x, 4x and 8x before adding Na₃VO₄. The concentration of H₂O₂ in each solution was determined as mentioned above by taking into account the dilution factors. The data are the mean ± SD of 9 independent experiments. For the experiments described in the panels C, D, E and F, the He flow was set to 50 sccm and the output voltage to 8 kV.