Continuous-flow sorting of microalgae cells based on lipid content by high frequency dielectrophoresis

This paper presents a continuous-flow cell screening device to isolate and separate microalgae cells (Chlamydomonas reinhardtii) based on lipid content using high frequency (50 MHz) dielectrophoresis. This device enables screening of microalgae due to the balance between lateral DEP forces relative to hydrodynamic forces. Positive DEP force along with amplitude-modulated electric field exerted on the cells flowing over the planar interdigitated electrodes, manipulated low-lipid cell trajectories in a zigzag pattern. Theoretical modelling confirmed cell trajectories during sorting. Separation quantification and sensitivity analysis were conducted with time-course experiments and collected samples were analysed by flow cytometry. Experimental testing with nitrogen starveddw15-1 (high-lipid, HL) and pgd1 mutant (low-lipid, LL) strains were carried out at different time periods, and clear separation of the two populations was achieved. Experimental results demonstrated that three populations were produced during nitrogen starvation: HL, LL and low-chlorophyll (LC) populations. Presence of the LC population can affect the binary separation performance. The continuous-flow micro-separator can separate 74% of the HL and 75% of the LL out of the starting sample using a 50 MHz, 30 voltages peak-to-peak AC electric field at Day 6 of the nitrogen starvation. The separation occurred between LL (low-lipid: 86.1% at Outlet # 1) and LC (88.8% at Outlet # 2) at Day 9 of the nitrogen starvation. This device can be used for onsite monitoring; therefore, it has the potential to reduce biofuel production cost