Development of novel energy-transferring nanomaterials which enhance the photophysical properties of light-harvesting proteins

Bio-hybrid nanomaterials have great potential for combining the most desirable aspects of biomolecules with the conceptual aspects of nanotechnology, both to potentially develop new technology for applications such as light harvesting, but also to understand fundamental properties of natural systems. The photosynthetic plant antenna protein light-harvesting complex II (LHCII) is extremely efficient at solar energy absorption and subsequent energy transfer in nature and has been demonstrated to perform effectively when incorporated into artificial nanoscale assemblies for light absorption. Here, we show that the effective absorption range of LHCII can be enhanced by interfacing the complementary lipid tagged chromophore, Texas Red DHPE, alongside LHCII in a model lipid membrane system which is self-assembled, modular, and readily adsorbed onto surfaces. Chapter 1 contains an overview of: photosynthesis in plants, the photo-physics of energy capture and transfer in antenna proteins, background on model lipid bilayers, and the development of bio-hybrid light harvesting materials. Chapter 2 summaries the methodology used in my PhD studies. Chapter 3 details the formation and spectroscopic characterisation of a new type of proteoliposome which were developed to interface the synthetic chromophore Texas Red to LHCII within a model lipid membrane. This successfully enhanced the overall absorption cross-section of the system. The proteoliposomes’ modularity was shown as the ability to incorporate a range of chosen concentrations of both Texas Red and LHCII and the energy transfer efficiency and enhancement of LHCII’s spectral range was quantified. In Chapter 4, proteoliposomes were deposited onto solid surfaces to allow the properties of individual membrane vesicles to be assessed and the population distribution to be quantified. This included measuring individual particle size, the co-localisation of LHCII and Texas Red, and energy transfer efficiency. Furthermore, membranes deposited on solid surfaces retained their energy transfer properties, demonstrating the potential for device-based applications for this concept. Finally, Chapter 5 details the adaptation of the LHCII and Texas Red system into lipid nanodiscs, which allowed the interactions between diffusing Texas Red molecules and single LHCII proteins to be investigated with ultrafast spectroscopy. This led to the quantification of the timescale of Texas Red to LHCII energy transfer and identification of sub-populations of energy donor molecules.