A Membrane-Confined Signal Amplification Strategy for Sensitive Monitoring of Extracellular Enzymatic Activity Upon Drug Stimulus.

Extracellular enzymes are not only strongly correlated with disease development but also play critical roles in modulating immune responses. Therefore, real-time monitoring of extracellular enzymatic activity can afford straightforward insights into their spatiotemporal dynamics upon drug stimulus, and provide promising tools to unravel their key roles in modulating the cell signaling. Although DNA-based sensing probes have been frequently developed for the detection of a variety of biomolecules, there still lacks a modular design strategy for amplified imaging of extracellular enzymatic activity associated with live cells. Herein, we developed an enzymatically triggerable signal amplification strategy for real-time dynamic imaging of extracellular enzyme activity through a cell membrane-confined hybrid chain reaction (HCR). We demonstrated that, by modifying the initiator DNA with enzyme-specific incision sites and cholesterol tail, extracellular enzyme-trigged HCR could be fulfilled on the surface of the cellular membrane, facilitating amplified detection of extracellular enzymatic activity. Dynamic monitoring of enzyme secretion of cancer cells upon stimulus or macrophage cells upon inflammation challenge has also been achieved. We envision that the design strategy could provide valuable information for dissecting the role of extracellular enzymes in modulating cell responses to drug treatment.