TCO-PEG4-TCO (CAS No.: 2243569-23-3) is a bifunctional click chemistry reagent. Its molecular structure consists of two trans-cyclooctene (TCO) groups at both ends connected by a flexible tetraethylene glycol (PEG4) segment in the middle. The production process employs chemical synthesis techniques (such as EDC/NHS activation of carboxyl groups) with precise control over PEG chain length and TCO coupling sites to achieve high purity (≥95%). This reagent is widely used in PROTAC molecule synthesis, intermolecular cross-linking, and labeling. Its TCO groups can rapidly react with tetracine-modified fluorescent dyes or radioactive isotopes, enabling real-time live-cell imaging and multimodal tumor diagnosis, making it of significant value in biomedical research and drug development.