The development of a biosensor for the detection of pathogenic bacteria in water

• Main Author: Wise, Naomi Victoria Jane
• Other Authors: Sheard, Stephen ; Thompson, Ian
• Published: University of Oxford 2015
• Subjects: 579.3
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.719856

Pathogenic bacteria are causative agents of epidemics and deaths worldwide; water is a vector for the transport of bacteria and their consequent consumption by humans. The accepted "gold standard" for assessing bacterial concentrations in water is by traditional plate counts. However, this globally accepted technique takes longer than 24 hours. An alternative method to rapidly detect and to continuously assess bacterial concentration is required. A biosensor that provides near real-time information on the bacterial loading of a waterbody is proposed. This thesis describes the development of a microfluidic-magnetophoretic device to detect bacteria in water. Escherichia coli is a well-reported bacterium found in the intestinal tract of mammals. Particular strains of E. coli are pathogenic to humans. E. coli is used as an "indicator" for water contamination and was chosen as the target for the biosensor. Magnetic particles (MPs) were functionalised with an anti-E. coli antibody. The functionalised MPs were used to capture E. coli from drinking water by forming MP-bacterial complexes. A microfluidic device was designed, incorporating magnetophoresis, to separate and concentrate MPs suspended within a sample. A separation efficiency of approximately 80% of the MPs from a sample flow was achieved. Using a magnetic gradient and video tracking of the MPs, the magnetic-drift velocities of unbound and bound MP-bacterial complexes was determined. It was found that viable and non-viable MP-bacterial complexes had different magnetically-induced drift velocities. A single viable E. coli bound to an MP travelled at 0.49 times the velocity of an unbound MP, and a single non-viable E. coli travelled at 0.75 that of an unbound MP. As such, this novel magnetophoretic separation technique can be used to determine the viability of bacteria. The developed biosensor provides the ability to concentrate, separate and enumerate viable E. coli from drinking water, with the potential for automation and sampling from continuous flow.