By Smitha Peter
Photosynthesis, the sophisticated technique used by plants to generate energy from water and sunlight, has caught the imagination of scientists for a long time. The process can produce an unlimited amount of hydrogen- which can be used as a ‘green fuel’ for vehicles and a clean source to generate electricity.
Plants generate energy directly from sunlight using light absorbing pigment chlorophyl. Image credit: The cat
However, the attempts to replicate photosynthesis have been met with limited success so far. It is mainly because of the challenges in designing a multi-component chemical system with exact structure of that present in the plant leaves.
A new study, published in Nature Nanotechnology by a team of scientists from Massachusetts Institute of Technology, is offering a solution for the problem regarding structural instability in artificial photosynthesis. The team, led by Dr. Angela M Belcher, constructed a stable nano structure for photosynthesis of water, using the genetically engineered M13 virus.
The role of spacial arrangement of chemicals in photosynthesis
In natural photosynthesis, chlorophyll, the light sensitive pigment present in the leaves, absorbs energy from sunlight initiating a flow of electrons through the leaf membrane. This finally leads to the splitting of water molecules into hydrogen and oxygen. The distance between the light harvesting chemicals involved is critically important, since non-optimal spacing can hinder the appropriate trafficking of electrons between individual active components. It results in degradation of catalysts and poor yield.
Genetically modified virus as a biological scaffold
The M13 virus DNA contains spiral proteins which are arranged in a highly ordered manner. Each protein wire contains two amines (N- terminus and lysine) exposed on the virus surface. Scientists attached photosensitiser zinc prophyrins and catalyst iridium oxide to the virus surface. So, the virus serves as a versatile template for assembling these chemicals and holding them in the correct position. The team also used a polymer microgel to encapsulate viruses. This prevented them from clustering, ensuring their homogeneous distribution.
Photosynthesis using this new method showed a dramatic increase in the water splitting activity. The high reaction rate is a result of electronic migration between photosensitisers and the close arrangement of photosensitiser and the catalyst.
Challenges in future
So far, the team has only succeeded in separating oxygen from the water molecule, which is considered to be the most difficult part of the process. The hydrogen produced is instantly split into its components protons and electrons. So the next challenge ahead is to bring these components together to collect hydrogen gas separately.
However, the researchers are optimistic about the future. According to an article in The Independent, they are hoping to convert it to a commercial product within a period of two years. This product can carry out oxidation of water with direct use of sunlight in a sustainable and efficient way.