Quantification of Microalgal Biomolecules Using Electrical Impedance Lumped Element Analysis

The microalga industry has garnered significant interest, particularly in the production of biodiesel and its applications in the food and pharmaceutical sectors. Lipids, proteins, and carbohydrates are the key elements of microalga cell biomass. The efficient on-site measurement and tracking of these biomolecules can improve the cultivation process, leading to optimal growth conditions. This study presents an innovative method that utilizes electrical lumped element modeling, derived from scattering parameter measurements, to simultaneously and noninvasively evaluate the levels of lipids, proteins, and carbohydrates in microalga cells, eliminating the need for any preliminary processing steps. This study focuses on the marine microalga cultivated under nitrogen-deficient conditions to encourage lipid accumulation to showcase the effectiveness of the proposed method. An open-ended RF biosensor was employed to perform reflection coefficient (S₁₁) measurements up to 13.6 GHz. The obtained input impedance was then matched to the relevant lumped element model. Remarkably, the changes in lipid content are reflected by shifts in the measured resonance frequency, while protein content changes show an inverse correlation with this frequency. Concurrently, the changes in both biomass dry weights and carbohydrate amounts are linked to variations in capacitance. The method's precision and dependability were verified by analyzing an independent sample. This approach facilitated rapid estimations of the microalga's intracellular makeup in few minutes, providing a substantial speed improvement compared to any analytical techniques or existing method, ever reported.