Coupling the COST reference plasma jet to a microfluidic device: a new diagnostic tool for plasma-liquid interactions

Plasma-liquid interaction processes are central to plasma applications in medicine, environment, and material processing. However, a standardized platform that allows the study of the production and transport of plasma-generated reactive species from the plasma to the liquid is lacking. We hypothesize that use of microfluidic devices would unlock many possibilities to investigate the transport of reactive species in plasma-treated liquids and, ultimately, to measure the effects of these species on biological systems, as microfluidics has already provided multiple solutions in medical treatment investigations. Our approach combines a capacitively coupled RF plasma jet known as the COST reference plasma jet with simple 3D printed microfluidic devices. This novel pairing is achieved by carefully controlling capillary effects within the microfluidic device at the plasma-liquid interaction zone. The generation and transport of reactive species from the plasma to the liquid inside the microfluidic device are analyzed using a colorimetric hydrogen peroxide concentration assay. A capillary flow model is provided to explain the two main regimes of operations observed in the device and their merits are discussed. Overall, the proposed plasma-microfluidic prototype shows great potential for the fundamental study of plasma-liquid interactions and opens the way to the use of standard microfluidic devices with plasma sources developing a plasma column or a plasma plume.