Phosphorescent oxygen-sensing and singlet oxygen production by a biosynthetic silk

A recombinant coiled-coil silk was utilised to immobilise heavy-metal-macrocycles which are known to undergo efficient intersystem crossing from the singlet state to the triplet state following excitation with visible light. This spin-forbidden transition leads to phosphorescence and the production of cytotoxic oxygen species. We explore the requirements for specific binding of these macrocycles and demonstrate that immobilisation does not adversely affect their photochemical properties. The biocompatible materials developed here have potential biomedical applications in photodynamic therapy (PDT) and dynamic oxygen-sensing.