Evaporating microfluidic droplets: A tool to study pathogen viability in bioaerosols

TL;DR

This paper introduces a microfluidic method to mimic evaporating bioaerosols, enabling detailed study of pathogen viability under extreme conditions like evaporation and osmotic stress.

Contribution

The study presents a novel microfluidic emulsion droplet technique to simulate evaporating aerosols and analyze pathogen survival in controlled microenvironments.

Findings

Evaporation rate negatively impacts E. coli viability.

Microdroplet clusters mimic bioaerosol evaporation dynamics.

Droplets serve as microreactors with variable kinetics.

Abstract

Pathogens in droplets on fomites and aerosols go through extreme physiochemical conditions, such as confinement and osmotic stress, due to evaporation. Still, these droplets are the predominant transmission routes of many contagious diseases. The biggest challenge for studying the survival mechanisms of pathogens in extreme conditions is closely observing them, especially in aerosols, due to the small droplet sizes, movements, and fast evaporative dynamics. To mimic evaporating aerosols and microdroplets, we employ microfluidic emulsion droplets. The presence of oil forms a microdroplet cluster with spatially gradient evaporation rates, which helps studying the impact of evaporation and its rate. With Escherichia coli, we show that the viability is adversely affected by the evaporation and its rate. Our method can mimic bioaerosol evaporation with controlled number of cells inside. In general, the droplets can act as microreactors with varying kinetics induced by different evaporation rates.