Antibody-Guided Proximity Labeling Enables Selective Chemical Modification of Exosome Surface Proteins

Exosomes have emerged as promising diagnostic biomarkers and therapeutic delivery vehicles, yet precise methods for their surface engineering without genetic manipulation remain limited. Here, we report an antibody-guided proximity labeling (PL) strategy for the selective chemical modification of exosome surface proteins. By employing an anti-CD63 antibody–HRP conjugate, we achieved localized oxidative generation of reactive species, specifically oxoammonium and iminoxyl radicals, that target tryptophan (Trp) and tyrosine (Tyr) residues in close proximity to the antibody. This approach enables efficient biotinylation of exosome surface proteins. Furthermore, we demonstrate that this PL platform can be applied directly to exosomes within cell-culture supernatants. This method provides a non-genetic tool for functionalizing native exosomes, facilitating their application in complex biological environments.