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

## TL;DR

The paper introduces a new method to create afterglow ice using luminophore-protein conjugates at freezing temperatures for potential bioassay applications.

## Contribution

The study introduces organic afterglow luminophore-protein conjugates and complexes at freezing temperatures for bio-labeling and sensing.

## Key findings

- Luminophore-protein conjugates exhibit afterglow at freezing temperatures due to hydrophobic and covalent interactions.
- Specific recognition of streptavidin by biotinylated luminophores activates organic afterglow.
- This work opens new possibilities for organic afterglow materials in bioassays and bio-labeling.

## Abstract

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.

While fluorophore-biomacromolecule systems are relatively well known, afterglow luminophore-biomacromolecule conjugates/complexes are rarely studied. Here, the authors report the development of a system with organic afterglow from luminophore-protein conjugates/complexes at freezing temperatures.