Afterglow ice formed by phosphorescent luminophore-protein conjugates and complexes in aqueous solution at freezing temperature

Unlike the widely reported fluorophore-biomacromolecule systems in nucleic acid testing and immunoassay, organic afterglow luminophore-biomacromolecule conjugates and complexes remain rarely explored. Here we report the observation of organic afterglow from aqueous solutions of luminophore-protein conjugates and complexes at freezing temperature, named as afterglow ice for abbreviation. Reliable N-hydroxysuccinimide ester protocol, as well as β-diketone chemistry, are applied for protein labeling to form luminophore-protein conjugates, which exhibit intriguing afterglow at freezing temperature. Control experiments reveal that hydrophobic interaction and covalent linkage between luminophore and protein can protect organic triplet excited states from quenching. In the case of luminophore-protein complex, we observe the switching-on of organic afterglow after specific recognition of streptavidin by biotinylated luminophore, which is the example of specific recognition and sensing of biomacromolecules by organic afterglow emitters. Although it is not yet a mature technology for biomedical applications, this study represents the initial step of organic afterglow materials towards bio-labeling and bioassay fields, as well as expanding the application scenarios of bioactive products.