Biomarker-Triggered Fluorogenic Label in Live Systems via Switchable Iminosydnone-Alkyne Cycloaddition

Precise spatiotemporal control over bioorthogonal labeling is crucial for studying biological processes in living systems. While external triggers like light offer control, methods responsive to intrinsic cellular stimuli remain scarce. Here, we report a modular, stimulus-activated bioorthogonal platform based on the iminosydnone-alkyne cycloaddition (ISAC). Inspired by the pronounced reactivity of N-unsubstituted iminosydnones, we developed a gating strategy by installing a cleavable, electron-withdrawing carbamate group at the 6-N position. This modification suppresses the cycloaddition with dibenzocyclooctyne until specific stimuli─including light, enzymes, or reactive oxygen species─remove the protecting group, rapidly restoring high reactivity. This turn-on reaction is accompanied by a fluorogenic response, enabling wash-free, stimulated-controlled fluorescent labeling of proteins and glycoproteins in live cells. Importantly, by leveraging cell-specific enzymes, we achieved selective protein labeling on target cells within cocultures, demonstrating exceptional spatial selectivity. This versatile platform provides a powerful strategy for interrogating biomolecular function with high precision in complex environments, holding great promise for studying intercellular communication and targeted delivery.