A 3D porous electrode for real-time monitoring of microalgal growth and exopolysaccharides yields using Electrochemical Impedance Spectroscopy

Efficient monitoring of microalgal growth is vital for biomass industrialization and management of water resources. The precise determination of growth phases of biotechnologically relevant species of microalgae is necessary as it allows controlling the onset of target metabolites production such as exopolysaccharides (EPS). However, a low-cost, real-time and ultrasensitive measurement method for direct determination of real-time microalgal growth and EPS production does not exist. Here, we show that Electrochemical Impedance Spectroscopy (EIS) in combination with porous polyurethane(PU)/poly (3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes can be used as a real-time probe to monitor microalgal growth and EPS production. We employ Lobochlamys segnis as a microalgae model system and show that growth can be continuously monitored with EIS for 14 days. A logistic growth rate from impedance data of k_Z = 0.75/day is found similar to that of conventional cell counting, of k_cells = 0.85/day, and is extracted from initial cell seeding densities as low as 10⁵ cells/mL. Furthermore, the Ohmic resistance of electrolyte solution enables the detection of the time-point of maximum EPS production. The combination of ultra-large porous electrodes with EIS provides a platform for sensing and modelling of microalgae growth in real-time and opens new avenues for predictive water resource management as well as more effective large-scale microalgal production in biotechnological applications.