Bacteria separation from diluted blood
Before testing the behavior of bacteria spiked in blood, we tested how bacteria behave in viscoelastic fluids. To demonstrate this, PEO was spiked with fluorescently labelled gram negative Escherichia coli(E.coli ) and gram positive Staphylococcus capitis (Staph)(107 CFU/mL) processed through the spiral device at a total flow rate of 1 mL/min in separate experiments. We observed a similar behavior for both gram negative and gram positive with an yield of 94% and 89% for E.coli and Staph respectively using agar plating based quantification (supplementary Fig.S1). Following, to study the separation of blood cells, lower concentration ofE.coli (103 CFU/mL) was spiked into 1:10, 1:5, and 1:2 diluted blood. As expected, the bacteria migrated to the inner wall and were collected at outlet O1, whereas blood cells stay near the outer wall and collected at outlet O2 (Fig.5A). Quantification performed using blood agar plating showed a separation efficiency of 82 to 90% ofE.coli (Fig.5B) depending on the dilution, while all blood cells were recovered through the outer outlet for all cases. The higher blood dilution, the higher bacteria separation efficiency, in agreement with the results obtained for 1 µm particles (see Fig.4). While high throughput is desirable for any application, need to process large volumes is extremely very important for sepsis applications. Ideally, this should not be on the cost of efficiency. Using our current spiral device, considering only the sample flow rate of 50 µL/min, it takes 40 minutes to process 1 mL of whole blood at a separation efficiency of 82%. To the best of our knowledge, this is the highest efficiency yet reported for a single device at an efficiency >80% using passive separation methods. On the other hand, for a separation efficiency of 90%, it would take approximately 3 hr to process 1 mL blood.