Abstract

In nature, charge recombination in light-harvesting reaction centers is minimized by efficient charge separation. Here, we show a new approach in which we aim to mimic nature by coupling dye-sensitized TiO₂ nanocrystals, CdS quantum dots (QDs) and carbon QD to the decaheme protein, MtrC and OmcA from Shewanella oneidensis MR-1, where the decahemes form a ~7 nm long molecular wire between the light harvesting nanoparticle (NP) and the underlying anode. The system is assembled by forming a densely-packed decaheme film on an ultra-flat gold electrode, followed by the adsorption of monolayer of NP. The step-by-step construction of the decaheme/NP system is monitored with (photo)electrochemistry, quartz-crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM). Interaction between NPs and decahemes is not solely due to electrostatic interactions, as TiO₂ nanocrystals with a negative zeta potential adsorb better on decaheme films than those with a positive charge, while for the CdS quantum dots the opposite is observed. When using TiO₂ nanocrystals, dye-sensitized with a phosphonated bipyridine Ru(II) dye, photocurrents are observed that are dependent on the redox state of the decaheme, confirming that electrons are transferred from the TiO₂ nanocrystals to the surface via the decaheme conduit.

In an extension to this system, the light harvesting nanoparticles are coupled to the transmembrane porin complex MtrCAB, which consist of 20 hemes that form a electron conduit through the lipid membrane. The aim of this system is to form a compartmentalised photocatalyst, where light-energized electrons outside the vesicles are transported to a catalyst encapsulated in the lumen of the vesicle. A proof of principle is provided using a redox active dye which bleaches upon (photo)reduction.