Plasma effects on the bacteria Escherichia coli via two evaluation methods

The degradation of Escherichia coli bacteria by treatment with cold, weakly ionised, highly dissociated oxygen plasma, with an electron temperature of 3 eV, a plasma density of 8 × 10^15 m^-3 and a neutral oxygen atom density of 3.5 × 10^21 m^-3 was studied. To determine the ＇real＇ plasma effects, two methods were used for evaluation and determination, as well as a comparison of the number of bacteria that had survived： the standard plate count technique （PCT） and advanced fluorescence-activated cell sorting （FACS）. Bacteria were deposited onto glass substrates and kept below 50 ℃ during the experiments with oxygen plasma. The results showed that the bacteria had fully degraded after about 2 min of plasma treatment, depending slightly on the amount of bacteria that had been deposited on the substrates. The very precise determination of the O flux on the substrates and the two-method comparison allowed for the determination of the critical dose of oxygen atoms required for the destruction of a bacterial cell wall--about 6 × 10^24 m^-2--as well as deactivation of the substrates--about 8 × 10^25 m^-2. These results were taken in order to discuss other results obtained by comparable studies and scientific method evaluations in the determination of plasma effects on bacteria.

Plasma-Induced Interfacial Processes in Metal Halides FTIR Gas Cell Windows

Fourier transform infrared spectroscopy(FTIR)is one of the most widely used vibrational diagnostic techniques to investigate gas-phase reactive oxygen and nitrogen species(RONS).However,the technique carries intrinsic challenges,particularly in relation to interfering peaks in the spectral data.This study explores the interfacial processes that occur when reactive oxygen and nitrogen species generated by a non-equilibrium air plasma interact with the metal halide windows of an FTIR gas cell,leading to the appearance and evolution of spurious absorption peaks which complicate spectral interpretation.Raman spectroscopy,X-ray photoelectron spectroscopy,time of flight secondary ion mass spectrometry and attenuated total reflectance-FTIR spectroscopy were used to elucidate the origin of spurious absorption peaks spanning the 1400-1300 cm^(-1)spectral range as a result of KBr exposure to plasma generated species.It was found that plasma exposed KBr contained a lower atomic fraction of Br which was replaced by the NO3nitrate group,the main absorbance peak of which progressively evolved with plasma exposure and affected the window transparency over the corresponding FTIR region.A correlation was revealed between KNO_(3)formation,plasma power and exposure time to a growth and change in molecular vibrational energies corresponding to asymmetric NO3stretching vibrations in the KNO_(3)structure.