Engineering hydrophilic/hydrophobic moieties of ratiometric fluorescence probe to visualize whole cytoplasmic polarity

Intracellular polarity is an essential parameter to indicate the property of microenvironment in the whole cell. The polarity is closely related to various physiological processes in different organelles and their changes in real time depending on the physiological/pathological activity. Visualization of whole cytoplasmic polarity is essential to understand the multi-organelle related pathological and biological phenomena. However, most of the reported single-organelle targeted fluorescent materials can only detect specific intracellular regions and normally with monotonic fluorescence changes. Herein, we engineered a polarity-sensitive probe 1P2N that install a cationic side alkyl chain on a push–pull type of pyrenyl-pyridium dye for whole cytoplasmic polarity visualization. Especially, this probe emits blue-green fluorescence from pyrene moiety in high-polar hydrophilic cytoplasm, while emits red fluorescence from intramolecular charge transfer process in low-polar lipidic organelles. The dual-emission response of 1P2N to polarity provides the basis for its ratiometric fluorescence monitoring of polarity changes in the whole cytoplasm under different physiological conditions. The excellent polarity-sensitive properties of probe 1P2N make it a useful tool for understanding polarity-related processes in the cytoplasmic microenvironment.