Dielectrophoretic Lipid Content Differentiation in Neochloris Oleoabundans for Biomass Harvesting Optimization

The dielectrophoretic behavior of Neochloris oleoabundans microalgae with heterogeneous cytoplasmic lipid content was characterized by dielectrophoresis using carbon interdigitated electrodes. For this purpose, two samples of microalgae were cultured: one under nitrogen-replete (N+) and the other under nitrogen-deplete (N-) conditions to allow low and high lipid growth, respectively. Cell population was monitored by spectrophotometry and the difference in lipid content among the samples was determined by Nile red fluorescence. The microfluidic device consisted of a carbon castellated microelectrode array fabricated using the Carbon-MEMS process—photolithographic patterning of a carbon precursor, followed by pyrolysis—bonded to a poly(dimethylsiloxane) microchannel. A Finite element model was developed to determine the electric field distribution across the microchannel and dielectrophoretic trapping zones. Experimental tests were carried out on wide frequency window (from 100 kHz to 30 MHz) at a fixed amplitude of 7 V_PP. Results showed a significant difference between the dielectrophoretic behavior of N+ and N- cells at low frequencies (100-800 kHz), whereas a weak response for mid and high frequencies (1-30 MHz). These results suggest that pyrolyzed carbon, obtained from a low-cost and straightforward fabrication process, is an attractive electrode material for microalgae dielectrophoretic characterization and isolation, based on their lipid content.