Development of bio-mimetic nano-compartments for solar energy capture

A growing range of artificial cell-mimicking compartments(e.g., liposomes) have been demonstrated as technological platforms for applications ranging from model systems in bottom-up cell biology to miniature chemical reactors. Here, I describe work on developing a liposomal compartment for capturing light-energy. The harvesting of light energy starts at a photoactive centre, where light-excited electrons are generated and then transferred to an electron acceptor. The efficiency of this electron transfer is often limited due to charge recombination (i.e., re-assembly of photo-separated electrons and electron holes) within the photoactive chromophore. Inspired by natural photosynthesis, this study envisions a strategy to limit charge recombination by rapid transfer of the lightexcited
electrons away from the photoactive molecules (dye-sensitized TiO2 nanoparticles or carbon dots) and across the liposome membrane via conductive transmembrane protein
complex MtrCAB from Shewanella oneidensis MR-1. Furthermore, such compartment enables localisation of the oxidation and reduction processes in separate environments.

The assembly of the envisioned compartment begins with a study of the molecular interface between TiO2 nanoparticles, a commonly used material for photocatalysis studies, and the MtrC(AB) conduit. This interface is mapped using an approach called protein footprinting, which involves protein labelling and subsequent analysis of the modified peptides by mass spectrometry. Understanding the molecular interactions at this bio-inorganic interface is crucial for engineering electronic communication between these materials. Then, a proof of concept is demonstrated of a half-reaction: light energy capture, charge separation across the membrane and use of the energy to drive a chemical reaction. Transmembrane electron transfer is achieved chemically and photochemically using dye sensitized TiO2 nanoparticles or carbon dots located outside the liposomes. The electron transfer through MtrCAB conduit is confirmed optically by monitoring the destructive reduction of an encapsulated azo-dye Reactive Red 120. Finally, work
on encapsulation of fuel evolving catalysts (i.e., hydrogen producing Pt nanoparticles and a hydrogenase HydA1) within the lipid-enclosed compartment (i.e., liposome lumen
and porous silica support) is discussed alongside the challenges for combining different materials within ordered structures.