Thesis (M.Sc.) - Cairo University - National Institute of Laser Enhanced Science - Department of Laser Applications Environmental Metrology Photochemistry and Agriculture

The use of CW laser light in two different biological applications (therapeutic and diagnostic) was investigated in this study. Firstly, a 405 nm diode-pumped solid state (DPSS) laser with output power of 100 mW was used as a therapeutic tool against two different species of bacteria in-vitro; Staphylococcus aureus as a gram positive model and Pseudomonas aeruginosa as a gram negative model. The bacterial cell suspensions prepared in 0.9% normal saline were irradiated directly in a 96-well microtitulation plate with 6 different doses (38.2, 76.4, 114.6, 152.8, 191.08, 229.2 J/cm2). Each species showed a different response to the treatment. P. aeruginosa showed a relative sensitivity to the treatment with a linear increasing pattern along with the doses applied. The maximum of 63.2% reduction in cell viability was observed with the maximum dose applied (229 J/cm2). On the other hand, S. aureus showed more resistance to the treatment resulting in a very slow decreasing pattern with the doses. Only 17.6% reduction in the cell viability was recorded as the maximum reduction with the maximum dose applied. Secondly, the laser induced fluorescence (LIF) technique was exploited as a diagnostic tool to simplify detection, and quantification of bacteria based on their auto-fluorescence abilities. Two laser excitation sources (405 nm and 266 nm) with two different bacterial species under investigation (P. aeruginosa and S. aureus) were assessed. The emitted fluorescence spectra were collected and analyzed, and the results came out proving that LIF is a promising technique that can help in discrimination and identification of cells as each sample showed a distinct fluorescence pattern. Also, fluorescence intensity showed an exponential relation with the concentration of the sample (log10 CFU/ml), which may be with further adjustment become helpful in identification of unknown samples. In order to visualize the induced fluorescence inside the cells, a confocal laser scanning microscope was employed revealing the shape of the investigated cells and the fluorescence emission at different wavelengths after excitation with 405 nm laser light which supported the results obtained by LIF

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