Faster and More Specific: Excited-State Intramolecular Proton Transfer-Based Dyes for High-Fidelity Dynamic Imaging of Lipid Droplets within Cells and Tissues

Abstract

Lipid droplets (LDs), a type of dynamic organelle residing at the center of cellular lipid storage, have been identified to play important roles in multiple biological processes, metabolic disorders, and diseases. The highly dynamic characters of LDs were found to correspond to their physiological and pathological functions. Hence, the fluorescent probes which enable dynamic tracking of LDs should be very helpful for better understanding the mechanisms of LDs involved biological processes and diseases. Herein we present, to the best of our knowledge, the first class of excited-state intramolecular proton transfer (ESIPT) fluorescence dyes (Flp-(11–13, 19)) for dynamic imaging of LDs based on 3-hydroxyflavone (3HF) derivatives. Flp-(11–13, 19) display strong fluorescence from yellow to NIR in lipid but exhibit almost nonfluorescence in aqueous solution. Besides, they also show large Stokes shifts (>150 nm), narrow absorption and emission peaks, and good oil–water separation efficiency, which makes them specifically target and stain LDs with very low background noisy in both living cells and fixed cells. They stain intracellular LDs quite quickly (within 30 s) with very low dosage (as low as 500 nM). Benefitting from these advantages, Flp-(11–13, 19) are applied successfully in tracking the dynamic nature of LDs and accumulation of LDs in both aqueous solution and living cells, 3D imaging of LDs for visualization of their repartition within the cells, and visualizing LDs in tissues of diseases mice models including adipose, skeletal muscle, and fatty liver tissues, underscoring the potential utility of these dyes in both LDs biology research and medical diagnosis of LDs involved diseases.

Time-resolved analysis of photoluminescence at a single wavelength for ratiometric and multiplex biosensing and bioimaging

“…21,22 Laser scanning confocal microscopy has been widely used for analyzing luminescence intensity of a probe to construct images, which simply and directly reect the spatial distribution and local concentration of the probe at the subcellular level. 23,24 Once the luminescence intensity of the probe is correlated with its specic interaction with functional biomarkers, luminescence imaging can locate and quantify the marker while continuously monitoring the process of life activities involved in the cell. [25][26][27][28][29] In order to improve the sensing and imaging accuracy and efficiency, it is usually necessary to employ multiple luminophores and simultaneously analyze two or more luminescence signals, thereby allowing one signal to be used as an internal standard, [30][31][32][33] or multiple signals to respond toward different targets.…”

Recent advances in fluorescent probes for lipid droplets

“…15). 34 They screened the derivatives with different p-substituted phenyl groups or furanyls. All these compounds showed strong fluorescence in organic solvents but weak fluorescence in water, accompanied by Stokes shifts over 150 nm.…”

Artificial Lipid Droplets: Novel Effective Biomaterials to Protect Cells against Oxidative Stress and Lipotoxicity

“…The average size of NLPs was 215.3 nm (Figure 1F). After staining with various neutral lipid dyes [27], all NLPs showed spherical structures, which indicated that they both contained a neutral lipid core (Figure S3).…”