Fluorogenic and Cell-Permeable Rhodamine Dyes for High-Contrast Live-Cell Protein Labeling in Bioimaging and Biosensing

The advancement of fluorescence microscopy techniques has opened up new opportunities for visualizing proteins and unraveling their functions in living biological systems. Small-molecule organic dyes, which possess exceptional photophysical properties, small size, and high photostability, serve as powerful fluorescent reporters in protein imaging. However, achieving high-contrast live-cell labeling of target proteins with conventional organic dyes remains a considerable challenge in bioimaging and biosensing due to their inadequate cell permeability and high background signal. Over the past decade, a novel generation of fluorogenic and cell-permeable dyes has been developed, which have substantially improved live-cell protein labeling by fine-tuning the reversible equilibrium between a cell-permeable, nonfluorescent spirocyclic state (unbound) and a fluorescent zwitterion (protein-bound) of rhodamines. In this review, we present the mechanism and design strategies of these fluorogenic and cell-permeable rhodamines, as well as their applications in bioimaging and biosensing.

Automated summary

The advancement of fluorescence microscopy techniques has provided new possibilities for observing proteins and understanding their functions in living biological systems. However, traditional organic dyes face challenges in achieving high-contrast live-cell labeling due to their insufficient cell permeability and high background signal. In recent years, a new generation of fluorogenic and cell-permeable dyes has been developed, which significantly improve live-cell protein labeling by fine-tuning the reversible equilibrium between a cell-permeable, nonfluorescent state and a fluorescent state of rhodamines. This review presents the mechanism and design strategies of these fluorogenic and cell-permeable rhodamines, as well as their applications in bioimaging and biosensing.