Development of a highly effective multi-stage surface acoustic wave SU-8 microfluidic concentrator

Abstract As an important step in sample preparation, sample concentration step helps to improve sampling techniques that are often necessary to detect low levels of pathogenic bacteria in food safety inspections, reducing or completely eliminating the need for time-consuming cell enrichment process for detection. In this study, we investigated strategies to significantly enhance performances of a surface acoustic wave (SAW) microfluidic device to concentrate various particles, including microbeads, bacterial and mammalian cells in suspensions. A low acoustic energy loss material, SU-8, was used to fabricate the microfluidic concentrator, and SAW reflectors were designed to efficiently use the SAW generated acoustic energy for particle concentration. The concentration performance was further improved by using a two-stage concentration design. We demonstrated that the SU-8 microfluidic concentrator with a two-stage concentration configuration was able to concentrate 2.00 μm bead samples at an overall concentration factor of ∼65-fold with a particle recovery efficiency of 81.9 ± 5.9% at a inflow rate of 300 μl/h. Similarly, when the concentrator was used to concentrate E. coli DH5α and NIH/3T3 cells, overall concentration factors of ∼59 and 75-fold with particle recovery efficiencies of 81.0 ± 17.2% and 90.8 ± 5.0% were obtained, respectively. These results show significant improvements upon those previously reported for either bacterial or mammalian cell concentration applications. In addition, the device fabrication process developed in this work is fully compatible with regular microfabrication processes, making this microfluidic concentrator readily integrable with other on-chip functionalities for cell manipulation and detection applications.