Shape-based separation of drug-treated <i>Escherichia coli</i> using viscoelastic microfluidics

Abstract

Here, we achieve shape-based separation of drug-treated <i>Escherichia coli</i> (<i>E. coli</i>) by viscoelastic microfluidics. Since shape is critical for modulating biological functions of <i>E. coli</i>, the ability to prepare homogeneous <i>E. coli</i> populations adopting uniform shape or sort bacterial sub-population based on their shape has significant implications for a broad range of biological, biomedical and environmental applications. A proportion of <i>E. coli</i> treated with 1 μg mL^-1 of the antibiotic mecillinam were found to exhibit changes in shape from rod to sphere, and the heterogeneous <i>E. coli</i> populations after drug treatment with various aspect ratios (ARs) ranging from 1.0 to 5.5 were used for experiment. We demonstrate that <i>E. coli</i> with a lower AR, <i>i.e.</i>, spherical <i>E. coli</i> (AR ≤ 1.5), are directed toward the middle outlet, while rod-shaped <i>E. coli</i> with a higher AR (AR > 1.5) are driven to the side outlets. Further, we demonstrate that the separation performance of the viscoelastic microfluidic device is influenced by two main factors: sheath-to-sample flow rate ratio and the concentration of poly-ethylene-oxide (PEO). To the best of our knowledge, this is the first report on shape-based separation of a single species of cells smaller than 4 μm by microfluidics.