Next, we performed the assay without acoustics to verify that the released bacteria stem from the trapping and not from side effects such as leakage between the cell suspension inlets or unspecific retention of bacteria in the channel. In contrast to the experiment with acoustics, we observed no cell accumulation at the wall and found the cell concentration at the outlet and inlet were nearly identical at 1 • 10 8 cells per mL during the first step ("capturing", but due to the absence of acoustic forces effectively just flushing of the tubing and chip with cell suspension). This suggests that no cells were actively trapped in the channel. Fur- thermore, during washing with ultrapure water, we still measured a bacteria concentration of 1.5 • 10 7 cells per mL in a total volume of 5 µL, which is in agreement with the assumption that at the beginning of the wash step the inner chamber of the device (approx. 1 µL of volume) was still filled with cell suspension. At the same time, this suggests no substantial leakage of cells from the cell suspension channel into the main channel during the wash step. Finally, during the third step of the protocol without acoustics, the cell concentration is 60-fold lower than during the capturing step. The strongly reduced cell number during the third step confirmed that the washing time and flow rate was sufficient to exchange close to all the residual volume in the chip and thus avoid cross-contamination between the cell suspension and the released cells in the new medium.