Credit: © 2010 NPG

Converting light into useable chemical energy is the driving force for life on Earth. Bacteria, algae and plants evolved with the ability to efficiently photosynthesize millions of years ago and scientists are playing catch-up. Now, in trying to reproduce photosynthesis artificially, they have taken a leaf out of nature's book and are trying to mimic the precise nanoscale organization of natural photosynthetic systems by optimizing the distance between functional components. To do this, Angela Belcher and colleagues from the Massachusetts Institute of Technology and Harvard University have used a genetically engineered 'M13' virus as a template that can organize important photosensitizer and catalyst molecules together on its surface1.

This spatial organization arises from the virus's highly ordered protein coat, which has exposed amine groups that Belcher's team used to chemically graft carboxyl-bearing photosensitive zinc porphyrin molecules. They then created core–shell nanowires by affixing a shell of iridium oxide — a water oxidation catalyst — to the virus's protein coat via a binding peptide. The team engineered a library of M13 viruses bearing random octameric peptides, and examined their affinities for binding indium oxide to determine which was most effective.

The co-localized IrO2–porphyrin nanowires oxidized water into molecular oxygen and protons far more efficiently than the control materials tested in which the same components were not spatially organized. The nanowires, however, were prone to aggregation, but after Belcher and colleagues immobilized them within a porous polymer microgel, their stability and recyclability were greatly improved.