Time-Resolved Single-Cell Assay for Measuring Intracellular Reactive Oxygen Species upon Exposure to Ambient Particulate Matter.

Health risks associated with exposure to ambient particulate matter (PM) are a major concern around the world. Adverse PM health effects have been proposed to be linked to oxidative stress through the generation of reactive oxygen species (ROS). In vitro cellular assays can provide insights into components or characteristics of PM that best account for its toxicity at a cellular level. However, most current assays report cell population averages and are mostly time endpoint measurements and thus provide no temporal information. This poses limitations on our understanding of PM health effects. In this study, we developed a microfluidic assay that can measure cellular ROS responses at the single-cell level and evaluate temporal dynamic behavior of single cells. We first established a protocol that enables culturing cells in our microfluidic platform and that can provide reproducible ROS readouts. We further examined the heterogeneous ROS responses of cell populations and tracked the dynamics of individual cellular responses upon exposure to different concentrations of PM extracts. Our results show that in an alveolar macrophage cell line, cellular ROS responses are highly heterogeneous. ROS responses from different cells can vary over an order of magnitude, and large coefficients of variation at each timepoint measurement indicate a high variability. The dynamic behavior of single-cell responses is strongly dependent on PM concentrations. Our work serves as a proof-of-principle demonstration of the capability of our microfluidic technology to study time-resolved single-cell responses upon PM exposure. We envision applying this high-resolution, high-content assay to investigate a wide array of single-cell responses (beyond ROS) upon exposure to different types of PM in the future.