Functional Raman Probes for Detecting Enzyme Activities Based on Aggregation Control

Visualizing specific enzyme activities in living systems is important in biomedical research, and Raman imaging probes are particularly suitable for simultaneous multiplexed detection of plural enzyme activities due to their narrow signal peak widths. Here, we present a molecular design strategy for enzyme-activity-detecting Raman probes based on control of aggregation. The probe itself is soluble and diffusive in aqueous solution due to its hydrophilic substrate moiety, but hydrolysis by the target enzyme affords a hydrophobic product that forms aggregates, thereby increasing the local dye concentration, which in turn results in a stronger Raman signal that enables visualization of the enzyme activity. We validated the molecular design by developing Raman probes targeting aminopeptidase, glycosidase and carboxypeptidase. The vibrational frequency can be shifted by isotope-editing, and the developed probes were successfully applied to visualize the activities of aminopeptidase and glycosidase in live cultured cells and spheroids.