(5b) Assessment of Microalgae Viability Employing Insulator-Based Dielectrophoresis

In recent years, numerous fields including environmental have increased their interest in microscale bioseparation systems. This is due to advantages brought by miniaturization such as requirement of small sample volumes, faster analysis, reduced costs, greater sensitivity and portability. Insulator-based dielectrophoresis (iDEP) is one of such systems where particles are driven by polarization effects in the presence of non-uniform electrical fields created by the inclusion of insulators between two electrodes. It has advantages over the common DEP approach, which is with the use of microelectrode arrays, since there is no degradation of the microelectrodes and are less expensive to manufacture1. DEP force depends highly on particle size and conductivity, in comparison with that of the suspending medium, and the gradient of the electric field applied. This means that if two particles have the same particle size will have different dielectrophoretic response if they present differences in conductivity, in the presence to the same electric field. It has been demonstrated that the cell's membrane state has an effect on the conductivity of cells1 and therefore DEP can be used to manipulate viable and non-viable Listeria2, Yeast cells3 and bacteria1. In the environmental field, assessment of microalgae viability is of great significance due to the ubiquity of these organisms in nature and multiple industrial applications. For example, microalgae are associated with toxins in water blooms, ecotoxicological tests, and wastewater treatment4. Therefore, to determine viable cells of microalgae after an algaecide application or as an indicator of pollutant remediation has important implications. Nowadays, microalgae are receiving great attention because of their significant potential as a source of energy and CO2 mitigation5. However, to explore, develop and implement these systems at the laboratory and field-scale depends in certain degree in methods that could promptly discern cell viability loss of the system. A rapid and reliable method to determine cell viability could improve and ascertain the success of all these biotechnologies. Considering the need for a technique or method that would allow for fast evaluation of the physiological/viability state of algal cultures, this study presents the application of iDEP to fractionate and concentrate viable and nonviable Selenastrum capricornutum cells, a unicellular eukaryote alga commonly used in ecotoxicological tests4. The work presented here is based on differences on membrane properties and have the advantage that dyes are no longer required once the technique has been tested and adapted. For the present work, a glass microchannel with cylindrical insulating posts was employed to dielectrophoretically immobilize and concentrate microalgae cells employing direct current (DC) electric fields. Experiments were carried out using live and dead microalgae cells, by varying the electric field in order to observe differences in their dielectrophoretic responses. Results showed that live and dead microalgae cells exhibit negative dielectrophoretic behavior when exposed to DC electric fields, where live cells exhibited a stronger dielectrophoretic response than dead cells6. Additionally, simultaneous enrichment and separation of live and dead microalgae was obtained, achieving different concentration enrichment. Successful immobilization y concentration of microalgae showing viability differences was achieved, demonstrating the great potential of iDEP as a technique for rapid microalgae viability assessment.

References 1. Lapizco-Encinas, B.H., Simmons, B.A., Cummings, E.B., Fintschenko, Y., 2004. Dielectrophoretic Concentration and Separation of Live and Dead Bacteria in an Array of Insulators. Analytical Chemistry. 76, 1571-1579. 2. Li, H., Bashir, R., 2002. Dielectrophoretic separation and manipulation of live and heat-treated cells of Listeria on microfabricated devices with interdigitated electrodes. Sensors and Actuator A. 86, 215-221. 3. Markx, G.H., Talary, M.S., Pethig, R., 1994. Separation of viable and nonviable yeast using dielectrophoresis. Journal of Biotechnolgy. 32, 29-37. 4. USEPA (1996) Ecological effects test guidelines: OPPTS 850.5400 Algal toxicity, tiers I and II. EPA712-C-96-164., U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Washington, D.C. 5. Wu Y., Huang C., Wang L., Miao X., Xing W., Cheng J., 2005. Colloids and Surfaces A: Physicochemical and Engineering Aspects 262:57-64. 6. Ozuna-Chacón S., Lapizco-Encinas B.H., Rito-Palomares M., Martínez-Chapa S.O., Reyes-Betanzo C., 2008. Electrophoresis 29:3115-3122.