Biomimetic Supported Lipid Bilayer on Thylakoid Membrane-Based Photobioelectrochemical System for Stability Enhancement

Abstract

Light-induced charge separation in photosynthetic reaction centers has a very high quantum yield. Due to this high quantum yield, bioenergy harvesting using photosynthesis of plant has been studied extensively. In the studies using algal cells or chloroplasts, their lipid membranes interfere with electron extraction. Therefore, most of studies are underway by using extracted photosynthetic organelles such as photosystems (PS I, II) and thylakoid membranes (TMs). However, without lipid membrane, the stability of photosynthetic organelles cannot be maintained. This is because photosynthesis generates reactive oxygen species (ROS) and protons that cause the degradation of photosynthetic organelles along with the production of high-energy electrons. On the other hand, chloroplasts have the internal environment separated by the lipid membrane to maintain homeostasis, which controls the level of ROS and pH within the chloroplasts.In this study, by mimicking chloroplast, we propose to form a biomimetic supported lipid bilayer (SLB) to maintain stability while constructing a TM-based photobioelectrochemical system. Alginate was used as a synthetic extracellular matrix (ECM), and SLB was formed with 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) through vesicle fusion. The swelling of the alginate prevents direct contact of TM-alginate composite film with the electrode and prevents separation of inside of the biomimetic protochloroplast from outside environment. To solve this problem, crosslink alginate with CaCl2 water solutions containing 20% ethanol to prevent warping of composite film and amino groups were created through silanization on ITO electrode to improve adhesion with film. Thereafter, SLB formation conditions were analyzed through confocal microscopy. With the formed DOPC SLB, it was verified by the dye release test whether the inside of protochloroplast was separated from the outside environment. Under the SLB-encapsulating environment, pH and ROS were controlled by ADP, ascorbate and glutathione. To confirm the improvement of the stability of TM, the long-term photocurrent was measured in the presence or absence of SLB and stability-maintaining materials. Moreover, SLB can act as a separator in electrochemical circuits due to its high electrical resistance. Electrical insulation property of SLB was confirmed using electrochemical impedance spectroscopy (EIS).