engleski

Characterization of oxygen plasma during degradation of Escherichia coli

Optical emission spectroscopy was applied for plasma characterization during sterilization of substrates contaminated with bacteria. The amount of 10cfi Escherichia coli was carefully applied to glass substrates and exposed to oxygen plasma at different pressure between 30 and 100 Pa. Plasma was created in a glass discharge tube by an inductively coupled RF generator at the frequency of 27.12MHz and output power of about 250W. The electron temperature and plasma density were estimated with a double Langmuir probe and were between 3 and 5 eV, and between 2 and 20x1016 m-3. Density of neutral oxygen atoms was measured with a catalytic probe and was between 2 and 6x1021m-3. Optical emission spectroscopy was performed with a low resolution spectrometer. The integration time of 300ms was enough to obtain measurable intensities of major spectral features. The predominant features were atomic oxygen lines, but other features including hydrogen, nitrogen, carbon monoxide and hydrogen oxide also appeared. The emission from carbon monoxide and OH molecules was used to monitor the evolution of bacteria degradation. Both signals expressed a well defined maximum corresponding to the peak erosion of bacteria by plasma radicals. As the sterilization was accomplished, both CO and OH bands fell below the detection limit of the spectrometer. The bacteria degradation was also monitored by scanning electron microscopy (SEM). The SEM images corresponded well with the evolution of CO and OH bands so the optical emission spectroscopy was found a reliable tool for monitoring the sterilization process.

oxygen plasma; plasma characterization; optical emission spectroscopy; Langmuir probe; catalytic probe; bacteria; sterilization; Escherichia coli

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