Morphology-Directed Light Emission from Fluorescent Janus Colloids for Pathogen Sensing

Pathogen sensors which are accurate, sensitive, cost-efficient, quick, and with minimal training are a continuing healthcare need. The chemical orthogonality of Janus droplets connects nano-scale chemical events into a structural response that is sensitive, inexpensive, and quick. Utilizing this chemo-morphological coupling, the detection of e.g., antibodies, pathogens, enzymes, PFAS, and metal ions, have been reported. While the connection between environmental change and droplet morphology is established, a method for simple and quick measurement of polydisperse samples is required, which would enable the deployment of Janus emulsion-based sensors without the need for precise droplet generation. Spherical Janus colloids with a morphology-tunable interface can totally internally reflect light dependent on morphology. Gravity-aligned Janus droplets with an internal refractive index contrast induce environmental and structural effects that contribute mutually to programmable optical behaviors. We investigate total internal reflection at the internal droplet interface, and the resulting morphology-determined anisotropy of both incident and emissive light. Using this angular emission, we present a ratio-metric sensing scheme to measure monolayers of polydisperse emulsion droplets responding to their chemical environment. Using this ratio-metric sensing scheme, these droplets were successfully used to detect three pathogenic bacteria from polydisperse emulsion droplets generated on-site, selectively, sensitively, and quickly. The reference-free detection of droplet morphology from macro-scale measurement has implications for the transduction of many existing surfactant chemistries. further understanding of directed anisotropic emission by spherical colloids has broad implications for the translation of nano-scale physical or chemical events into readily available macro-scale information.