Microscopic algae are a promising future platform for the sustainable production of biofuels. These organisms use sunlight, atmospheric carbon dioxide, and nutrients such as nitrogen and phosphorous dissolved in liquid medium to make lipids which can be processed into liquid transportation fuel. The growth of algae in outdoor open ponds, and the accumulation of lipids by the algae, can vary considerably during the day or week. This requires frequent monitoring of algal productivity for production planning. However, measurement of algal productivity is presently time consuming and costly, requiring manual sampling and sophisticated analytical instruments. The goal of this project is to develop a simple, real-time sensor for monitoring algal lipids in a cultivation environment that is constantly changing. The proposed work will develop a sensor platform that measures the electrical properties of single algal cells as they flow through a microscope capillary tube. The change in electrical properties is correlated to the amounts and types of lipid stored within the algal cell. The educational activities associated with the project feature a student-run technical conference designed to diversify and provide mentorship for students in the Mechanical Engineering graduate program at Cornell University.
In outdoor pond cultivation systems used for algal biofuel production, the growth and lipid accumulation in algal cells are sensitive to constantly changing liquid nutrient medium composition, temperature, and sunlight intensity. Co-cultures containing two or more species of algae that have disparate metabolisms and chromophores may add stability to the overall cultivation platform under these changing conditions. However, lipid production in algal cells is often triggered by nutrient starvation, which adds to the temporal complexity of the system. There is a need to monitor and summarize all of this biological complexity with simple measurements that describe the overall lipid productivity of the co-culture as well as lipid productivity of individual sub populations. The proposed research will develop a microfluidic dielectric impedance monitor for rapid lipid detection in single algal cells and characterize lipid storage in algal co-cultures to elucidate mixed-strain culture effects. The project has three objectives. The first objective is to characterize starvation-induced, dielectric-property shifts in Chlorella vulgaris, Chlamydomonas reinhardtii, and Neochloris oleoabundans and relate these shifts to biomass density and sequestration of lipids and starches. The second objective is to validate the flow-impedance cytometry measurements of lipid and starch accumulation by nuclear magnetic resonance (NMR) and high-performance liquid chromatography. The third objective is to characterize the role of algal diversity with single-cell and bulk characterization of lipids in mixed-species culture.
