Red emissive carbon dots as a fluorescent sensor for fast specific monitoring and imaging of polarity in living cells

Polarity is an integral microenvironment parameter, which is crucial for establishing and reflecting a large number of sophisticated physiological functions and pathological effects. Monitoring changes in intracellular polarity is of great scientific and practical significance. In this work, we present a highly-fluorescent red-emitting carbon dots (CDs) based fluorescent sensor for the specific real-time sensing of polarity in solutions and living cells. Both the fluorescence and absorption wavelengths displayed a large redshift to the red emission region with increasing solvent polarity. Inspired by the excellent photostability and photobleaching resistance, high fluorescence quantum yield, superior interference immunity, negligible cytotoxicity and significant biocompatibility, the sensor has been successfully implemented as an effective diagnostic candidate for monitoring and imaging the polarity changes in mitochondria and lysosomes. This work can not only present effective strategies for the design and synthesis of red/near-infrared (NIR) emissive CDs but also afford promising tools for the selective, sensitive, rapid, real-time visualizing detection of polarity in living cells, as a consequence accelerating a better understanding and diagnosis of polarity-related physiological and pathological processes and diseases. This work presents red emissive CDs as a promising fluorescent sensor with excellent photostability, high fluorescence quantum yield, and negligible cytotoxicity for real-time sensing and visualizing polarity changes in mitochondria and lysosomes.