Microplasma Generation of High Fluxes of Singlet Delta Oxygen at Atmospheric Pressure for Biomedical Applications
Atmospheric pressure generation of singlet delta oxygen (SDO) by microplasmas has been experimentally studied. ln this work, we have used a specific type of microdischarges, called MCSD (microcathode sustained discharges), which have allowed the operation of DC glow discharges, free from the glow-to-arc transition. From electrical and optical diagnostics, the reduced electric field (E/N), the gas temperature (Tgas), the atomic oxygen density profiles, the ozone spatial distribution, as weIl as the SDO density have been obtained for several operating conditions. Our results show that MCSD are similar to high-pressure positive columns, with low values of E/N (5-10 Td) and of Tgas (300-700 K). Thus, MCSD fulfill aIl the required characteristics for an efficient production of SDO. It must be pointed out that, due to its remarkable stability, the MCSD is, to this date, the only discharge technique that has been proven capable of generating high fluxes of SDO at atmospheric pressure. By optimizing the operation of arrays of several MCSD, we have efficiently produced and transported at atmospheric pressure, over distances longer than 50 cm, SDO densities higher than 10 to the power of 17 cm-3. Additionally, O3 densities up to 10 to the power of 16 cm-3 have also been obtained. As the ratio density of SDO to O3 can be finely and easily tuned in the range [10 to the power of -2 - 10 to the power of +5], our plasma source is unique in the context of the new research field of Plasma Medicine. Indeed, we have shown that arrays of MCSD are very useful tools for examining in detail the reactivity of these reactive oxygen species towards DNA. ln collaboration with biologists, we have determined the damages induced in DNA by SDO and O3.