Tracking plasma generated H₂O₂from gas into liquid phase and revealing its dominant impact on human skin cells

The pathway of the biologically active molecule hydrogen peroxide (H 2 O 2 ) from the plasma generation in the gas phase by an atmospheric pressure argon plasma jet, to its transition into the liquid phase and finally to its inhibiting effect on human skin cells is investigated for different feed gas humidity settings. Gas phase diagnostics like Fourier transformed infrared spectroscopy and laser induced fluorescence spectroscopy on hydroxyl radicals ( · OH) are combined with liquid analytics such as chemical assays and electron paramagnetic resonance spectroscopy. Furthermore, the viability of human skin cells is measured by Alamar Blue® assay. By comparing the gas phase results with chemical simulations in the far field, H 2 O 2 generation and destruction processes are clearly identified. The net production rate of H 2 O 2 in the gas phase is almost identical to the H 2 O 2 net production rate in the liquid phase. Moreover, by mimicking the H 2 O 2 generation of the plasma jet with the help of an H 2 O 2 bubbler it is concluded that the solubility of gas phase H 2 O 2 plays a major role in generating hydrogen peroxide in the liquid. Furthermore, it is shown that H 2 O 2 concentration correlates remarkably well with the cell viability. Other species in the liquid like · OH or superoxide anion radical do not vary significantly with feed gas humidity.