BODIPY/Nile-Red-Based Efficient FRET Pair: Selective Assay of Endoplasmic Reticulum Membrane Fluidity

We synthesized a boron‐dipyrromethene (BODIPY)/Nile Red hybrid probe capable of selectively recognizing fluidity changes in the endoplasmic reticulum (ER) membrane due to its preferential localization to the ER and strong energy transfer from BODIPY to the Nile Red moiety, emitting only in nonaqueous environments. ER membrane fluidity in HepG2 cells was markedly reduced by a cell model of metabolic syndrome. Don′t FRET: A local environment‐sensitive BODIPY‐Nile Red efficient FRET pair was developed to selectively observe the membrane fluidity of the endoplasmic reticulum in HepG2 cells.