Acoustic square microchannel for improving focusing efficiency of sub-micron particles and bacteria

Abstract

Flow cytometry is a technique that observes each cell with fast speed and informs whether it is positive for a selected determinant. One problem of this technology when trying to observe sub-micron size particles is their weak fluorescence intensity. If focusing ability is not enough, particles flow far from the center in the microchannel, and its fluorescence intensity goes even lower than that of background noise. In this paper, focusing ability of fabricated acoustofluidics for sub-micron particles and bacteria is mainly discussed. The device consists of a square microchannel of 100 µm × 100 µm and surface acoustic wave (SAW) transducer to make acoustic wave into the microchannel. To prevent confliction of acoustic radiation force and acoustic streaming induced drag forces, the transducer is operated with a 7.39 MHz frequency which make half wavelength resonance in the microchannel. In the experiment, polystyrene beads with diameters 3.25 µm, 1.33 µm and 0.5 µm is used to general focusing ability, and two bacteria (Enterobacter cloacae and Escherichia coli) are used to evaluate applicability of this device in the biological field. 3.25 µm and 1.33 µm beads are focused well until the flow rate of 80 µL min-1. The focusing ability for 0.5 µm beads are maintained until 8 µL min-1. In cases of bacteria, the device focuses Enterobacter cloacae and Escherichia until 10 µL min-1 and 5 µL min-1 respectively. Based on the results, the device can focus on sub-micron particles and bacteria. Therefore, it could be applied to flow cytometry.