Generation and delivery of free hydroxyl radicals using a remote plasma

We demonstrate a new gas-based OH center dot generation source using a low power radio frequency driven atmospheric pressure plasma configured to deliver the radical flux into the far effluent region, well away from interference from other plasma factors such as electric fields, currents, and ultraviolet radiation. Using He-H2O gas chemistry isolated from the laboratory air, the plasma generated flux contains OH center dot and other radicals including, O and HO2 as well as H2O2 which, along with, was found to vary with H2O vapour content and absorbed power density. Peak flux values were 2.3 nmol s(-1) and 0.23 nmol s(1) for H2O2 and OH center dot respectively at a distance of 50 mm from the plasma, with 790 ppmv H2O and a power density of similar to 10(8) W m-3. The maximum OH center dot flux density was 4.5 x 10(19) m(-2) s(-1) falling to 1.7 x 10(19) m(2) s(1) at 110 mm, equivalent to generation rates of 74 mu M s(1) and 28 mu M s(-1). Despite high OH center dot recombination rates at the plasma exit, the escaping flux is still significant, indicating a viable delivery capability to downstream targets. Its performance with regard to OH center dot generation rates compares well with traditional OH center dot generation techniques such as radiolysis, advanced oxidation processes and enhanced Fenton-chemistry approaches where OH center dot production rates are sub-mu M s(-1). Delivering precisely quantifiable OH(center dot )fluxes provides new opportunities for scientific studies and technological opportunities in cell biology, atmospheric chemistry, protein unfolding and systematic dose studies for plasma-based and other OH center dot related potential medical treatments.

Automated summary

We have developed a gas-based OH generation source using a low power radio frequency driven plasma. This source delivers OH radicals away from interference and has been found to vary with H2O vapour content and absorbed power density. The OH flux generated has been compared to traditional OH generation techniques and shows promising results for various scientific and technological applications.