Controlling reactive species in plasma jets for future precision medicine
Shuai Zhao defended his PhD thesis at the Department of Applied Physics and Science Education on March 10.
Shuai Zhao has developed an advanced diagnostic platform to precisely measure and control biologically active species produced by atmospheric pressure plasma jets (APPJs), a promising technology for next鈥慻eneration medical treatments. His work brings plasma therapy closer to becoming a safe, reliable, and personalized tool in healthcare.
Plasma jets as a 鈥渂lade of light鈥� in medicine
APPJs generate reactive oxygen and nitrogen species (RONS), including atomic oxygen (O) and nitric oxide (NO), by activating the surrounding air. These species play a double role in biology: in the right amounts, they can kill antibiotic鈥憆esistant bacteria, stimulate blood vessel dilation, and promote wound healing; but in excessive concentrations, they may harm healthy tissue. For decades, the lack of tools to measure and control these species in real time has been the main barrier to clinical adoption.
Zhao鈥檚 research addresses this challenge head鈥憃n by establishing a diagnostic system that can quantify O and NO production with nanosecond temporal and millimeter spatial resolution. This allows researchers to map out how plasma jets behave and to determine exactly which device parameters lead to safe and beneficial therapeutic doses.
Mapping O and NO generation with high鈥憄recision diagnostics
Using a combination of laser鈥慽nduced fluorescence (LIF), optical emission spectroscopy (OES), and iCCD imaging, Zhao characterized the chemical pathways that lead to O(鹿S) and NO formation in argon plasma jets. His measurements reveal how species densities change with voltage, flow rate, frequency, and gas composition, essentially creating a digital prescription for plasma鈥慴ased treatments.
He also identified two distinct plasma discharge regimes, diffuse and DAF (diffuse-filamentary), each associated with different levels of green O(鹿S) emission. These insights provide a deeper understanding of how electron density and temperature shape reactive species production.
Understanding plasma鈥搇iquid interactions
Because many biological systems and agricultural environments are water鈥慴ased, Zhao also investigated how plasma jets interact with liquid surfaces. Water was found to significantly influence NO production by altering the chemical pathways inside the plasma, especially through the role of OH radicals.
Experiments comparing different water conditions, such as heated, grounded, or saline water, show that plasma diagnostics must treat the plasma source and the target surface as a coupled system. This finding is crucial for designing plasma devices that can safely treat real biological tissues.
Toward 鈥渟mart plasma systems鈥�
Looking ahead, Zhao envisions Smart Plasma Systems: medical devices capable of automatically adjusting their O and NO output based on patient鈥憇pecific needs. These systems could deliver precise, controlled doses for wound care, infection treatment, and tissue regeneration.
Beyond medicine, the diagnostic principles developed in this thesis have potential impact in green chemistry, sustainable agriculture (e.g., plasma鈥慳ctivated water for nitrogen fixation), and advanced semiconductor surface processing, where high鈥憄recision control of reactive species is essential.
-
PhD student
Shuai Zhao, Department of Applied Physics and Science Education
Read more -
Supervisors
Ana Sobota & Gerrit Kroesen