A Concerted Enzymatic and Bioorthogonal Approach for Extra-cellular and Intracellular Activation of Environment-Sensitive Ruthenium(II)-Based Imaging Probes and Photosensitizers

In this work, we demonstrate a synergistic approach by combining an EISA moiety with a strained cycloalkyne to generate large accumulation of bioorthogonal sites in cancer cells (Figure 1). These bioorthogonal sites can serve as activation triggers in both extracellular (plasma membrane) and intracellular (mitochondria) regions for our newly designed metal-based probes, which are ruthenium(II) complexes carrying a complementary bioorthogonal functional group for controllable phosphorescence and singlet-oxygen generation. Importantly, the environment-sensitive emission of the ruthenium(II) complexes can be further enhanced in the hydrophobic regions offered by the large supramolecular assemblies, which is highly advantageous to biological imaging by increasing the signal-to-noise ratio. Additionally, the extracellular and intracellular (photo)cytotoxicity of the large supramolecular assemblies with the ruthenium(II) complexes was investigated, and the results illustrate that cellular localization imposes a profound impact on the efficiencies of photosensitizers.