Polarity-triggered high-contrast fluorescent imaging of lipid droplets via a naphthalimide fluorophore

Abstract

Lipid droplets (LDs) are complex and dynamic organelles and involve in a variety of biological processes. Notably, some severe diseases are usually initiated by aberrant alterations of LDs. Consequently, the development of reliable methods is essential for elucidating the biological functions of LDs. In this study, an ICT-based naphthalimide fluorescent probe NA-LD was elaborately designed and synthesized for high-contrast and specific imaging of LDs. NA-LD was constituted of 1-ethynyl-4-methoxybenzene (the electron-donor group), diamide (the electron-accepter group), and the 2-ethylpyridin (balancing the lipophilicity and hydrophilicity). A series of analyses demonstrated that NA-LD exhibited high lipophilicity (ClogP = 5.8), large Stokes shift (Δλmax = 201 nm) and excellent biocompatibility. Additionally, NA-LD showed sensitive fluorescent response to polarity in a linear range from Δf = 0.228 to 0.301, and fluorescence intensity of NA-LD in low polarity was 101-fold stronger than that of in high polarity media. Furthermore, the specific, high-contrast and dynamic imaging of LDs was successfully achieved, as well as the obvious difference of LDs between cancer cells and normal cells was observed. All these features render NA-LD a practical tool for deciphering mechanism of LDs-related diseases.