Serial Separation of Microalgae in a Microfluidic Chip Under Inertial and Dielectrophoretic Forces

There are a large number and variety of microalgae in the ocean, which are important natural resources for extensive applications. However, how to identify and separate microalgae quickly and effectively remains a major challenge for investigation and utilization of microalgae resources. There are many methods for cell separation, while each of them has pros and cons. Therefore, it is difficult to meet the particular requirements of separating complex samples, such as microalgae, solely with a single method. Herein, a two-stage microfluidic separation chip was designed by combining inertial and dielectrophoretic (DEP) forces, which can achieve rapid and accurate separation of three common microalgae cells, including Platymonas, Closterium and Chlorella, with separation efficiency exceeding 90%. In the first-stage, high-throughput inertial separation technique was used to separate microalgae with their different equilibrium positions. Then, the DEP force was used to separate microalgae cells which were not separated in the first-stage through their dielectric properties. To the best of our knowledge, there is no prior reports of microalgae separation by combining DEP and inertial techniques. In addition, the DEP characteristics of microalgae cells under a non-uniform AC electric field were firstly reported in this study, and the DEP responses of each cell type were measured against AC electrical frequency changes. These findings may contribute to our understanding of the dielectric properties of microalgae, as well as the development of novel techniques for microalgae separation, detection, and marine environmental monitor and analysis.