Use of frequency swept ultrasound to manipulate Nb2-11 live cells in a microfluidic channel

Recently microfluidic manipulation of live cell has been attracting attention because it is necessary for fast and accurate bioassays of cells within miniaturized devices like a lab-on-a-chip. This work concerns the alignment, translocation and concentration of live cells in a microfluidic channel by utilizing an ultrasonic standing wave. Among many ultrasonic manipulation methods, the technique using frequency swept ultrasound which was proposed in a previous study offers excellent particle manipulation performance, but that has been demonstrated only for biocompatible polystyrene microspheres with several different diameters, not actual biological cells. However, the technique needs to be verified for real cells because sizes and properties are little different with each other. Thus, in this work, the feasibility of using the ultrasonic frequency sweep method to manipulate live Nb2-11 cells was investigated experimentally The cells were aligned in a plane, moved to one side of a channel, and finally filtered out by sending them to one outlet with ultrasound. The frequency region of the applied ultrasound was between 1.75 MHz and 3.05 MHz. From experimental results, the cell behavior showing perfect alignment, almost perfect translocation and hence considerable aggregation proved the feasibility of using the frequency sweep method though the force acting on the Nb2-11 cells are much smaller than the force acting on polystyrene beads due to the differences in their sizes and mechanical properties.