Detection of protein-protein interactions by bio-orthogonal fluorogenic proximity probes

Detecting protein-protein interactions within cells is challenging. Transgenic approaches risk altering protein function via fluorescent tagging, while in situ methods lack in vivo compatibility. Here, we introduce fluorogenic probes with dual-tetrazine pegylated branched arms linked to xanthene dye. Activation requires both tetrazine arms to interact simultaneously with target proteins, enabling dual-substrate recognition. We applied our method to detect protein-protein interactions in both fixed and living cells, utilizing antibody conjugation for fixed cells and genetic code expansion for real-time detection in living cells. Our strategy ensures versatile applicability and seamless transition between fixed and living systems.