Journal: medRxiv

Article Title: A Cascaded Droplet Microfluidic Platform Enables High-throughput Single Cell Antibiotic Susceptibility Testing at Scale

doi: 10.1101/2021.06.25.21259551

Figure Lengend Snippet: (A)(i) In the absence of barrierplugs, picodroplets can disperse as they flow through the incubation channel and cause significant mixing among picodroplet groups. (ii) Such dispersion and mixing can be fluorescently detected as picodroplet groups with distinct fluorophore concentrations would yield a fluorescence trace showing mixed peaks ( i . e ., picodroplets) with distinct avalanche photodiode (APD) photon counts ( i . e ., fluorescence intensities). (B)(i) Two-dimensional water-oil multiphase flow CFD simulation reveals that, within an oil-filled, 500-µm-wide microchannel (white) and under pressure-driven flow, a water barrierplug (black ellipse, 1000 μm × 500 μm semiaxes) that seals the entire width of the channel flows faster than a downstream water picodroplet (black circle, 25 μm in diameter, indicated by black arrows) that is positioned at the wall of the channel, as indicated by the decreasing distance between them over time (t = 0, 1, 2, and 3 s). (ii) Experimental observation within the incubation channel of a SCALe-AST device corroborates with the simulation, as a barrierplug indeed catch up to picodroplets at the channel wall over time (t = 0, 3, 6, and 9 s). (C)(i) In the presence of barrierplugs, which prevent dispersion of picodroplets, picodroplet groups therefore become tightly packed and well separated from each other. (ii) Well separated picodroplet groups due to the addition of barrierplugs can be fluorescently detected as picodroplet groups with distinct fluorophore concentrations could now yield a fluorescence trace showing well separated groups of peaks with distinct photon counts.

Article Snippet: To test this hypothesis, we first created a two-dimensional multiphase computational fluid dynamics ( i . e ., CFD) simulation using COMSOL.

Techniques: Incubation, Dispersion, Fluorescence