Radio-frequency oxygen plasma as a sterilization source

An oxygen plasma sustained at 13.56 MHz in a standardized reactor with a planar induction coil was used for biological decontamination experiments. Optical emission, mass spectrometry, Langmuir probe, and electrical measurements were applied to detection of chemical species and ion-energy and flux analysis. These diagnostics identified a plasma-mode transition in the range of 13-67-Pa pressure and 100-330-W power to the induction coil. At higher pressure and lower power, the plasma was sustained in a dim mode (primarily by stray capacitive coupling). A primarily inductive bright mode was attained at lower pressure and higher power. The coupling mode of plasma operation was then monitored by emission spectroscopy on an analogous, scaled-down reactor for biological degradation tests. Plasmid DNA degradation efficacies were compared in both plasma modes. DNA removal was similar to25% more efficient in the inductively coupled mode than in the capacitively coupled mode at the same power. The fast degradation was attributed to synergetic mechanisms (photo- and ion-assisted etching by oxygen atoms and perhaps O-2(*) metastable molecules). Volatilization rates of the decomposition products (CO2, CO, N-2, OH, H) evolving from the microbial (Deinococcus radiodurans) and polypeptide samples exposed to the plasma were compared. A plasma sustained in Martian atmosphere is considered.