Semi-permeable membrane stabilized microfluidic plasma chip for continuous, tunable synthesis of sub-10 nm nanoparticles

Atmospheric-pressure microplasma, characterized by its gaseous electrode containing tunable electrons and reactive species, can initiate reactions at the plasma/liquid interface. Integrating microplasma into a microfluidic chip can confine reactions to the microscale, enhancing uniformity and controllability. However, maintaining a stable gas/liquid interface in microchannels is inherently challenging due to Rayleigh-Plateau instability and perturbing pressure gradients. In this study, we designed a microfluidic plasma chip stabilized by a semi-permeable membrane for dielectric barrier discharge microplasma-assisted reactions. This hydrophobic porous membrane blocks liquid while allowing plasma to pass through, enabling independent biphasic control. Using gold nanoparticle synthesis as a model, we achieved a size ranging from 7.31 to 11.32 nm and a standard deviation of 1.8 nm, by detailed parameter study. The planar microplasma facilitates uniform, precise, and tunable reactions with short-lived and highly localized reactive species, making this approach suitable for challenging applications such as selective synthesis, pollutant degradation, and biomedical diagnostics.