Optical feedback control loop for the precise and robust acoustic focusing of cells, micro- and nanoparticles

Despite a long history and the vast number of applications demonstrated, very few market products incorporate acoustophoresis. Because a human operator must run and control a device during an experiment, most devices are limited to proof of concepts. On top of a possible detuning due to temperature changes, the human operator introduces a bias which reduces the reproducibility, performance and reliability of devices. To mitigate some of these problems, we propose an optical feedback control loop that optimizes the excitation frequency. We investigate the improvements that can be expected when a human operator is replaced for acoustic micro- and nanometer particle focusing experiments. Three experiments previously conducted in our group were taken as a benchmark. In addition to being automatic, this resulted in the feedback control loop displaying a superior performance compared to an experienced scientist in 1) improving the particle focusing by at least a factor of two for 5 μm diameter PS particles, 2) increasing the range of flow rates in which 1 μm diameter PS particles could be focused and 3) was even capable of focusing 600 nm diameter PS particles at a frequency of 1.72075 MHz. Furthermore, the feedback control loop is capable of focusing biological cells in one and two pressure nodes. The requirements for the feedback control loop are: an optical setup, a run-of-the-mill computer and a computer controllable function generator. Thus resulting in a cost-effective, high-throughput and automated method to rapidly increase the efficiency of established systems. The code for the feedback control loop is openly accessible and the authors explicitly wish that the community uses and modifies the feedback control loop to their own needs.