Single Fluorescent Probe for Zero-Crosstalk Discrimination of Lipid Droplets and the Endoplasmic Reticulum Based on Reversible Cyclization Reaction

The interactions between different organelles are ubiquitous and crucial for life activities. Thus, development of a single fluorescent probe enabling the simultaneous two-color visualization of two organelles is of great significance for the study of organelle interplay. Herein, using the reversible ring-opening/closing reactions of rhodamine dyes, we have fabricated a robust fluorescent probe to distinguish lipid droplets (LDs) and the endoplasmic reticulum (ER) in dual-emission channels with negligible crosstalk. The probe 6′-(diethylamino)-4′-((7-(diethylamino)-2-oxo-2 H -chromen-3-yl)methylene)-1′,2′,3′,4′-tetrahydro-3 H -spiro[isobenzofuran-1,9′-xanthen]-3-one, which was sensitive to the changes in the water content in the organism, displayed strong green fluorescence in the hydrophobic LDs from its ring-closed form, while it existed in a ring-opened form in the ER to illuminate a strong near-infrared emission. Importantly, the spectral difference was up to 320 nm, and thus the crosstalk between two channels was negligible. With the unique probe, the lipid accumulation in cells treated with different concentrations of oleic acid, cholesterol, and stearic acid has been successfully observed. The changes of LDs and the ER in living cells stimulated by temperature changes and hypoxia stimulation have also been revealed. Meanwhile, the different sizes and distribution of LDs and the ER in various tissues were also studied using the robust probe. This work provides a new approach to the design of dual-emissive probes and contributes to a significant molecular tool to promote the study of organelle interactions.