Bacteria separation and enrichment using viscoelastic flows in a straight microchannel

Bacteria occupy a large domain of prokaryotic microorganisms on earth and play a significant role in public health. In this study, we achieve continuous size-based bacteria separation using viscoelastic flows in a microchannel. Three types of bacteria that differ in size, including Lactobacillus rhamnosus (L. rhamnosus), Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli) are employed. First, the separation of L. rhamnosus and S. epidermidis is investigated. Under the combined effects of inertial lift and elastic forces, the larger L. rhamnosus cells are driven toward the channel centre while the smaller S. epidermidis cells flow in narrow streams along the channel sidewalls. The results show that the separation performance of the viscoelastic microfluidic device is affected by four main factors: channel length, total flow rate (TFR), sheath-to-sample flow rate ratio (FRR) and polyethylene oxide (PEO) concentration. Furthermore, the separation of L. rhamnosus and E. coli is demonstrated. This work overcomes the issues like shape irregularity and size variation in bacterial samples and achieves the separation of two types of bacteria in a size-dependent manner. We expect that this work will facilitate the future studies of bacterial interspecies communication and interactions as well as the development of biology, biomedicine and biotechnology.