Hydrodynamic flow cytometer performance enhancement by two-dimensional acoustic focusing

Conventional flow cytometers employ hydrodynamic focusing method to insure detection accuracy by forcing cells go through detected position. However, an increased flow velocity will significantly reduce detection precision due to a fact that cells will deviate center position and are easily silted in choke point. In an effort to overcome this limitation, a two-dimension ultrasonic particle focusing method are presented in this work to enhance the performance of flow cytometer. Two piezoelectric transducers are used to attach to a 250 μm × 250 μm rectangular fused silica flow channel to realize the modification. Finite element model simulation is performed for parametrical analysis and simplifying experiment design. 3 μm polystyrene fluorescent particles are adopted to test focusing effect. One dimension acoustic focusing is achieved at 2.95 MHz with single focusing node as well as 2, 3, 4 nodes focusing near 6, 9, 12 MHz respectively. The 2D focusing particle stream width in two dimensions is less than 10 μm. Results verified that this method is applicable for Jurkat cells. Sample flow maintains its stability without clogging up even at high sample concentration. Focusing still works at flow velocity over 100 μl/min. All these results certify this acoustic particles focusing method can enhance the performance of hydrodynamic flow cytometer by minor modification.