Generation and delivery of free hydroxyl radicals using a remote plasma

TL;DR

This paper introduces a novel low-power RF atmospheric pressure plasma source that generates and delivers hydroxyl radicals (OH) remotely, with potential applications in scientific research and medical treatments due to its high OH flux capabilities.

Contribution

The study presents a new gas-based OH radical generation method using remote plasma, achieving high flux rates and isolating OH production from other plasma effects, which is a significant advancement over traditional techniques.

Findings

Peak OH flux of 0.23 nmol s-1 at 50 mm distance

Maximum OH flux density of 4.5 x 10^19 m-2 s-1

Comparable OH generation rates to traditional methods

Abstract

We demonstrate a new gas-based OH generation source using a low power RF-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 UV radiation. Using He-H2O gas chemistry isolated from the laboratory air, the plasma generated flux consists of H2O2 and OH, varying 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 respectively at a distance of 50 mm from the plasma, with 790 ppmv H2O and a power density of 1E8 W m-3. The maximum OH flux density was 4.5 x 1E19 m-2 s-1 falling to 1.7 x 1E19 m-2 s-1 at 110 mm, equivalent to generation rates of 74 uM s-1 and 28 uM s-1. Despite high OH 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 generation rates compares well with traditional OH generation techniques such as radiolysis, advanced oxidation processes and enhanced Fenton-chemistry approaches where OH production rates are sub-uM s-1. Delivering precisely quantifiable OH 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 related potential medical treatments.