Dependence of the dielectrophoretic upper crossover frequency on the lipid content of microalgal cells

• Published in: Algal research (Amsterdam) 2014-10, Vol.6, p.17-21
• Main Authors: Michael, Kelsey A., Hiibel, Sage R., Geiger, Emil J.
• Format: Article
• Language: English
• Subjects: High frequency dielectrophoresis; Lipids; Microalgae; Upper crossover frequency
• ISSN: 2211-9264; 2211-9264
• DOI: 10.1016/j.algal.2014.08.004

High frequency dielectrophoresis (>20MHz) was used to demonstrate that the upper crossover frequency of microalgal cells is reduced as lipids accumulate within the cytoplasm. Currently, the majority of AC dielectrophoresis applications differentiate cells by exploiting differences in the lower crossover frequency, typically between 10 and 500kHz. However, the single shell model also predicts another crossover in the 20–200MHz range that is dependent upon the dielectric properties of the cytoplasm. We demonstrate this effect with microalgal cells due to the relative ease in which the properties of the cytoplasm can be altered. Chlamydomonas reinhardtii cells were cultured in regular media and were observed to have an upper crossover frequency of ~75MHz. The same cells, when cultured under nitrogen-free conditions, began to accumulate neutral lipids. The lipid content was verified via fluorescence microscopy and the upper crossover frequency was measured to be ~40MHz. To measure the upper crossover frequency, two needle shaped electrodes were patterned onto a glass slide and the motion of the cells was observed as an AC signal was swept from 10–110MHz at ~30 voltage peak-to-peak (Vpp). We conclude that the increase in lipid content reduces the effective conductivity of the cytoplasm thus reducing the upper crossover frequency. High frequency dielectrophoresis may be a label free technique to sort algae cells on the basis of lipid content. •Algae cells were grown such that there were low lipid cells and lipid rich cells.•Increased lipids in cytoplasm change the intrinsic dielectric properties of a cell.•Lipid rich cells have a lower crossover frequency when compared to low lipid cells.•Separation of high and low lipid algal cells may be possible via dielectrophoresis.