A new design for living cell-based biosensors: Microgels with a selectively permeable shell that can harbor bacterial species

Biosensors integrating genetically programmed living cells into hostile and synthetic environments ( e.g. , devices or matrices) provide powerful tools for scientific research and enable new technological applications. However, it remains a challenge to maintain the viability and functionality of the living components exposed to different chemical, physiological or mechanical conditions in specific applications. To this end, we report herein a microfluidic approach to encapsulate microorganisms in gel-shell beads (GSBs) as a novel kind of biosensor. Inspired by biosilicification, hydrogel beads are coated with a mesoporous shell that can prevent cell leakage and afford mechanical stability, with the porous hydrogel structure naturally providing sustained supplies of water and nutrients to the embedded microorganisms. Communications between compartmentalized bacterial strains and the environment is achieved through the diffusion of signalling molecules across the mesoporous shell. Application of GSBs as living cell-based sensors is exemplified in a quorum sensing system, where genetically engineered Escherichia coli cells are encapsulated in GSBs and can respond to autoinducer concentrations ranging from 10 −6 to 10 −7 mol/L as secreted by human pathogen Pseudomonas aeruginosa in the infection site.