Inner workings of photosynthesis revealed by powerful new laser technique

Instant pictures showing how the sun's energy moves inside plants have been taken for the first time, according to research out on Friday 6 February in Physical Review Letters.

Astra laser

The images unravel some of the inner workings of the most efficient solar energy process on earth - photosynthesis. Inside a photosynthetic protein, the sun's energy is efficiently guided across the molecule to drive a chemical reaction that stores energy as food and takes in carbon dioxide. Scientists would very much like to harness this process as they search for new energy solutions to replace fossil fuels. To do this, they need to understand this energy transport process in more detail.

Analysing energy transport is an important way of understanding the inner workings of a wide range of systems, from biological processes to car engines. However, in very small-scale systems such as photosynthetic molecules, quantum effects come into play making it difficult for scientists to explain how photosynthetic molecules are able to transport energy with remarkably high efficiency.

Until now, one of the major obstacles has been the lack of a direct way of probing some of the fundamental mechanisms involved in the flow of energy between electrons in molecules.

"These new pictures are instantaneous snap-shots of energy being transported between electrons across a protein. Remarkably, the pictures go further in unravelling the complex way the electrons interact. This gives us something akin to a fingerprint for electronic couplings," says Dr Ian Mercer from the School of Physics at University College Dublin, the lead author of the new study, who is a visiting researcher at Imperial College London.

The researchers probed a sample of a protein found in bacteria, called LH2, which was provided by the University of Glasgow. This bacterial protein was used because it harvests light in the same way as photosynthetic plant proteins. By illuminating the sample with a combination of high power laser pulses all derived from the same laser, the researchers obtained a map of bright spots on a camera in a tiny fraction of a second. The position of each spot corresponds to a unique angle of light emitted from the sample and this directly relates to how electrons in the protein respond to the laser light and to each other.

Alternative laser-based techniques for gathering such information do already exist, but require the sample to be exposed to the laser light for a long period, which may lead to sample degradation. They also require much more intensive computer processing.

Astra laser

The researchers needed a very powerful and stable laser in order to get the new approach to work efficiently and accurately. They used the Astra laser at the Science and Technology Facilities Council's (STFC's) Rutherford Appleton Laboratory (RAL). It incorporates state-of-the-art technology developed in the Physics Department at Imperial College London to produce pulses of light with the right properties for this experiment.

"The laser produces a very broad range of colours, which allowed us to map a broad range of energy levels in the protein. The availability of this laser source at RAL, which is accessible to a broad range of scientists, opens up a lot of new and exciting science - like this work", explains co-author of the study, Dr John Tisch from Imperial College London's Department of Physics.

With this laser, a map can be captured with a single pulse of laser light meaning that full information can be gathered prior to, or during, a chemical reaction. The technique can also be used to characterise high-value, delicate samples because only a small quantity of sample is required. And with one thousand laser pulses available per second from the laser, there is potential for rapid automated sample characterisation.

"More demonstrations are around the corner. Hopefully one day we will be able to harness the exquisite mechanisms that we learn about from molecules, whose function has been honed by evolution over hundreds of millions of years", says Dr Mercer. The researchers are currently applying this approach across the molecular biosciences and with electronic devices.

"Dr. Mercer's work illustrates one of the broad range of applications the STFC's advanced laser technology has in addressing real-world problems across many scientific disciplines." Professor John Collier, Head, High Power Laser Programme.

Notes for editors

Images

Images of the Astra laser are available from the Press Office, contact details are below.

Contacts

• Lucy Stone
  STFC Press Officer
  Rutherford Appleton Laboratory
  Tel: + 44 (0)1235 445627
  
  
• Danielle Reeves
  Imperial College London press office
  Tel: + 44 (0)207 5942198
  Out of hours duty press office: + 44 (0)7803 886248
  
  
• Dominic Martella
  External Communications Manager
  University College Dublin, Irelan
  Tel: + 353 (1) 7161681
  Mobile: + 353 (0)872959118

Further information

'Instantaneous mapping of coupled electronic coherences and energy transfers in a photosynthetic complex using angle-resolved coherent optical wave-mixing,' Physical Review Letters, early online publication, Volume 102, issue 5, 6 February 2009.

• Ian P Mercer (1)
• Yasin C El-Taha (2)
• Nathaniel Kajumba (2)
• Jonathan P Marangos (2)
• John W G Tisch (2)
• Mads Gabrielsen (3)
• Richard J Cogdell (3)
• Emma Springate (4)
• Edmund Turcu (4)

• (1) School of Physics, Centre for Synthesis and Chemical Biology, University College Dublin, Dublin 4, Ireland
• (2) Quantum Optics and Laser Science Group, Blackett Laboratory, Imperial College, London, UK
• (3) Biochemistry and Molecular Biology, Faculty of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
• (4) Central Laser Facility, STFC Rutherford Appleton Laboratory, Didcot, UK

About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London (link opens in a new window) is a science-based institution with a reputation for excellence in teaching and research that attracts 13,000 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve health in the UK and globally, tackle climate change and develop clean and sustainable sources of energy.

About University College Dublin

For over 150 years, University College Dublin (link opens in a new window) (UCD) has produced graduates of remarkable distinction including leading surgeons, architects, entrepreneurs and five of Ireland's Taoisigh (Prime Ministers). Perhaps the best known of all its graduates is the writer James Joyce, who completed his Bachelor of Arts at the university in 1902.

Established in 1854, UCD played a key role in the history of the modern Irish State and today it plays a leading part in shaping Ireland's future. Each of the five colleges at the university has its own dedicated graduate school with the explicit task of enhancing doctoral and post-doctoral training to match the national strategy of establishing Ireland as a premier source of 4th level education and research.

About the University of Glasgow

The University of Glasgow is one of the top 100 universities in the world (Times Higher World University Rankings 2006). Established in 1451, it is the fourth oldest university in the UK with currently 16,000 undergraduates, 4,000 postgraduates and 4,000 adults in continuing education. Alumni include scientist Lord Kelvin, political economist Adam Smith and the pioneer of television, John Logie Baird. The main campus is centred on a neo-Gothic main building designed by Sir George Gilbert Scott in 1870. Its distinctive spire is an iconic city landmark. The University is a research powerhouse with an annual research contract income in the top 10 of UK universities.

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