Conductive thylakoid composites with mussel-adhesive protein-coated carbon nanotubes for harvesting photosynthetic electrons

Abstract

Photosynthetic electrons (PEs) can be extracted electrochemically from photosynthetic apparatus such as photosystems I & II, cytochrome b6f complex, and plastocyanin of thylakoid membranes (TMs). However, as in photovoltaic systems, efficient transfer of PEs, which are generated from the photosynthetic apparatus, to an anode is extremely challenging. Although electrochemical mediators have been employed for this purpose, ultimately, direct electron transfer is preferred through electrical networks among the photosynthetic apparatus and an anode. In this work, we dramatically increased contact area through carbon nanotubes (CNTs) percolation network by a simple method of mixing TMs and CNTs that are coated with mussel-adhesive protein (MAP) for uniform dispersion and attachment to TMs. Formation of electrical percolation network within the thick composites of MAP-CNT/TMs was confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Compared to TMs with a mediator, 10 times higher photocurrents were recorded from the composites of MAP-CNT/TMs without a mediator. Finally, with a thick MAP-CNT/TMs composite layer (equivalent to 500 μg of Chlorophyll a), photocurrent of 4.25 μA cm−2 was produced without aid of a mediator.