A nanostructured cell-free photosynthetic biocomposite via molecularly controlled layer-by-layer assembly

Abstract Thylakoids, on which complete sets of photosynthetic membrane proteins are contained, behave as soft nanoparticles of a few tens nm sizes. Thus, we separated the thylakoid extracts from spinach chloroplasts and densely organized them in a film with either insulating polyethyleneimine (PEI) or conducting polyaniline (PANI) by molecularly controlled layer-by-layer (LBL) assembly. The resulting nanostructured composite films demonstrated photoelectrochemical activities with thylakoids whose stabilities were significantly improved on the charge balanced LBL multilayers compared to one on a randomly deposited film or in solution. The thylakoid LBL films continuously generated photochemical electrons for longer than 130 h with the 2,6-dichlorophenolindophenol (DCPIP) mediated photosynthetic energy conversion cycle while photoactivities of thylakoid moiety slowly decreased in the open circuit potential measurements throughout which the photosynthetic redox cycles were incomplete. As the photofunctional groups of the thylakoid films originated from a biotic system and the photofuctional thylakoids were exceptionally well preserved on the charge-balanced artificial structures, the developed thylakoid LBL film have shown inherent biocompatibility upon PC12 neural cell attachment and differentiation tests, which are essential qualities for emerging human-friendly electronic applications such as disposable electronics, artificial retina, and implantable neural interfacing meditronics as well as cell-free photosynthetic production.