BBSRC-NSF/BIO: Quantum-enhanced long-range energy capture

Photosynthesis powers life on Earth, providing all of our food, oxygen and most of our energy. The general principles underpinning the first steps of photosynthesis have been conserved by evolution; a protein network, termed the antenna, captures solar energy and delivers it to a dedicated protein, the reaction center, where electricity is generated.

Remarkably, these steps can occur with almost 100% quantum efficiency. Recent observations suggest that nature may achieve this high efficiency by utilizing wavelike transport of absorbed solar energy from the antenna to the reaction centers. However, the presence and role of such quantum mechanical phenomena in natural systems are highly debated.

One challenge to characterizing their impact has been that experiments on the antenna were performed in non-native and isolated solutions. In this project, which is a collaboration between researchers at the Michigan Institute of Technology (US) and the University of Sheffield (UK), the investigators will attempt a step-change in our understanding by investigating how solar energy is transported within the native network.

These experiments will simultaneously uncover the mechanisms that give rise to efficient capture and conversion of solar energy to electricity and identify the interactions that enhance or repress the underlying quantum behaviors. They will then seek to exploit these natural design principles to build non-native systems with enhanced abilities to propagate energy efficiently over increased distances.

These studies will thereby lay the groundwork for improving energy transport in biohybrid and semi-conductor devices for application to emerging technologies relevant to consumer electronics, solar energy capture, quantum computing, quantum communications and photocatalysts. The project will simultaneously train the next generation of researchers at the biology/physics interface and disseminate the fascinating fundamental science underpinning natural solar energy conversion to the general public.

In photosynthetic light harvesting and solar energy conversion, the protein architecture involved varies dramatically with species, yet the general design is conserved; a network containing light-harvesting complexes (LHCs) absorbs and transfers energy to a reaction center (RC) for charge separation. Remarkably, absorption to charge separation can occur with almost 100% quantum efficiency.

Experimental observations of oscillations within the excited state manifold led to a body of theoretical work that suggested the high efficiency is, in part, due to quantum coherence. However, the measured oscillations have been increasingly assigned to vibronic coherences, and experimental evidence of quantum coherence or its role in light harvesting has been elusive.

To date, experiments have all been performed on isolated LHCs and RCs, yet these proteins function natively within a network. Furthermore, non-native interactions introduced through lithography have been shown to enhance the properties of the LHC, including energy transport and oscillator strength from exciton-plasmon coupling. Thus, the behaviors within the native network as well as the ability of non-native interactions to impact this behavior have not been investigated.

In this project, the investigators will use different in vitro platforms to replicate the native network and introduce non-native interactions for different combinations of photosynthetic proteins. They will use advanced spectroscopy and microscopy to characterize excited-state properties, energy transport, solar energy conversion, and network geometry.

The results will provide a blueprint for how nanoscale organization and interactions direct energy for light harvesting and solar energy conversion.

This collaborative US/UK project is supported by the US National Science Foundation and the UK Biotechnology and Biological Sciences Research Council.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.