Launching a Tug-of-War between Bacteria and Bi-phase Droplets

The development of rapidly deployable, point of care sensors for detecting bacteria is necessitated by the ever- present and serious public health threat they continue to pose. However, the ability to discern between dead and live populations or quantifying their viability remains a non-trivial challenge to address. Here, we develop simple droplet based optical micro-transducers that can not only readily distinguish between live and dead bacteria but are also capable of gauging the metabolic levels of individual cells by tracking the time dependent force generated by a bacterium with sub piconewton resolution. We engineer the mesogen ordering in complex colloidal droplets comprising of immiscible liquid crystal (LC) and fluorocarbon phases, to create topological singularities for the selective localization of mannose functionalized polymer surfactants for conjugation with Escherichia coli cells. The asymmetry in density induced by the two-phase morphology induces a dynamic tug-of-war between the torque applied by the swimming bacteria and opposing gravitational forces. This dynamic interaction and the underlying mechanism are investigated through controlled experiments and modelling. These results provide a demonstration of tunable liquid systems that deliver robust optical responses via chemical coupling with biological organisms.  They find utility in the development of both rapidly deployable pathogen sensing systems and biologically powered micro-actuator systems.