Laser decontamination and detection of bacteria and microalgae

Jaafar, Weaam (2015) Laser decontamination and detection of bacteria and microalgae. PhD thesis, University of Glasgow.

Abstract

There are many harmful airborne microorganisms which can be breathed in by animals or humans and lead to illness or even death. Such organisms can land on surfaces or in liquid leading to other opportunistic routes to infection such as touch and ingestion. Consequently, there is a need to develop novel forms of decontamination and detection of pathogens in air, on surfaces and in liquids. The present work investigates these areas and in particular assesses the impact of novel laser and plasma decontamination systems on inactivation of Bacillus atropheaus spores, an anthrax simulant, in aerosols and on surfaces. To further evaluate the performance of the methods, it was necessary to identify how the spores flowed through the systems. Experiments were devised to quantify the effect of flow shaping and the electrode’s surface roughness, on the spore deposition.

The spatial distribution of B. atropheaus spores on the electrodes was determined by using two methods, either a membrane filter or an imprinting (pressing) technique. Rougher surfaces allowed a higher level of microorganisms adhesion compared to smooth surfaces. The angle of incidence of the flowshaping on the spore distribution was investigated by using two angles, 10° and 30°. The capture was quantified by the number of spores that were counted on agar plates following incubation. The number of colony forming unit CFU was greatest near the entry point, and generally reduced along the electrodes’ length and was also greater for the 30° inlet angle. Computational Fluid Dynamics (CFD) techniques were applied to model the particular flow through the electrode geometry and for the laser decontamination system.

Methods of spatial detection of microorganisms on surface were further developed using microscopy methods. Three methods were used in this research: optical microscopy examination to find the minimum detectable level of B. atrophaeus spores on surfaces, a fluorescence technique using LEDs was developed to investigate the spatial detection of spores and microalgae and a flow chamber system was developed that was used for cell counting of microalgae in liquid.
The effect of excimer laser radiation on Escherichia coli vegetative cells and Bacillus atrophaeus spores was investigated. E. coli or B. atrophaeus spores were lawned onto agar plates and treated with pulsed excimer laser radiation at 248 nm. The plates were incubated overnight at 37 °C and assessed for areas of clearing or inactivation. The applied pulse energy was 37 mJ, the pulse repetition frequency (PRF) was either 20 or 100 Hz, exposures were from 1-10 pulses, or up to 1 min. The range of applied energy densities was from 0.31 to 18500 Jcm-2. Image processing techniques were developed to determine the cleared area, major and minor axis and fractional clearing away from the region directly exposed to the laser beam. The area of clearing was approximately linear for treatment against E. coli, and was non-linear against B. atrophaeus. Increasing the PRF increased the area of clearing, as did increasing the exposure time. Interestingly, these areas of clearing were much greater than the beam area (2 x 6 mm), suggesting that scattering of the radiation played a significant role in contributing towards inactivation away from the directly laser exposed region. The results showed that excimer lasers offer the potential for rapid decontamination of microorganisms and spores on surfaces. Simple protocols allow direct comparison of the inactivation efficacy of different laser sources and image processing techniques can be applied to accurately quantify these results.

Growing and harvesting microalgae is important for sustainable and secure biofuel and food production. There is a wide spread interest in growing and exploiting the microalgae. The lipid, protein, carbohydrate and vitamin content of microalgae are not only species dependent but are also a function of their growth parameters such as nutrient, light, temperature and CO2. The importance of detection of microalgae on assessing optimal growth conditions was investigated, along with the impact of harvesting and lipid extraction. Image processing systems were developed to quantify the size distribution of microalgae as a determinant of growth efficiency.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Watson, Dr. Ian
• Date of Award: 2015
• Depositing User: Mrs Marie Cairney
• Unique ID: glathesis:2015-6172
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 06 Mar 2015 16:48
• Last Modified: 06 Mar 2018 09:04
• URI: https://theses.gla.ac.uk/id/eprint/6172