The Spatial Dependent Interaction of Environment Controlled Atmospheric Pressure Plasma Jets with Cultured Cells

The recent innovation of atmospheric pressure plasma jets (APPJs) has shown great potential in a variety of medical applications, especially as a therapeutic tool for cancer treatment. Due to the complex physical interactions of plasma in the atmosphere and in contact with liquid, a rich chemical environment of reactive species is produced. Such an environment can provoke a number of biological effects, including impairment of cell substructures and even cell death. Since the application of a plasma jet on a cell target is an areal treatment, the spatial distribution of the species in the plasma jet, the species delivered into the liquid, and the biological responses can provide critical insights in understanding the spatial dependent interactions between plasma and cellular systems.

The spatial investigation of cellular effects induced by plasma treatment can also reveal essential information, such as the size of the treated area, and the effectiveness in the treated area. This is a rarely reported aspect of plasma treatment due to the lack of techniques and analysis methods that are able to reveal spatial information over a large cell growing region (order of cm2) while also provide detailed cellular feature information. Therefore, as the first parts of my dissertation, I introduced a systematic large-scale image processing with machine learning for data analysis. I introduced the usage of fluorescence slide readers for acquiring images covering the entire cell region, and developed several novel computational methods, such as SALR clustering to accurately localize the cell centers, and cell-cycle classification using only a single DNA marker with fluorescence microscopy. I then applied these methods to reveal the spatial distribution of plasma induced DNA damage.

To overcome the sensitivity of plasma jets due to the variation of surrounding environment, I designed and constructed a plasma device with shielding gases to control and tune the distribution of the plasma species. Spatial scans of the optical emission spectra from the plasma jet and a gel based reactive species detector were applied to investigate the spatial distribution of reactive species in the gas phase and the liquid phase, respectively. Significantly, a larger effective area with higher damage, especially in S-phase cancer cells, were observed with a N2 shielding gas, when compared to any other shielding gas, suggesting nitrogen species plays a critical role in inducing DNA damage.