A Chemical Approach To Synthetic Quorum Sensing

Quorum sensing is a biological phenomenon in which both stimuli and response are directly linked to population density. This process of collective behaviour is used by bacteria to regulate gene expression within bacterial colonies. This is achieved by the production and release and detection of signalling molecules known as autoinducers. Until very recently synthetic quorum sensing has been achieved by either; the ‘splicing’ of the quorum sensing machinery from one bacterial host to another; or chemically through derivatives of the oscillating Belousov-Zhabotinsky reaction. More recently there has been a shift to developing collective behaviour through the immobilisation of enzymes within polymer hydrogels.
This thesis is focused upon the development of a truly synthetic quorum sensing system. This is achieved by replicating the component technologies of biological quorum sensing with synthetic equivalents. A truly synthetic quorum sensing system requires; (i) the autonomous aggregation of particles; (ii) the generation of a signal by the particles; (iii) the detection of the signal; (iv) a response by the particles which only occurs when the population of the aggregate is above a threshold level.
In order to observe signal detection and response ratiometric imaging microscopy is retooled and used for the first time to observe continuous diffusion of a signal from its host. To meet the requirement of signal generation the enzyme glucose oxidase is used. This enzyme converts glucose to gluconic acid which results in the lowering of pH. To ascertain its suitability the action of glucose oxidase in solution was probed. Hydrogel particles of alginate were loaded with glucose oxidase and magnetite. The magnetite enables spontaneous aggregation to occur when the particles are placed within a magnetic field. The resulting signal generation and response of particle clusters of differing populations was observed with a ratiometric imaging setup. This results in the demonstration of a robust synthetic quorum sensing system.