Interface-targeting strategy enables two-photon fluorescent lipid droplets probes for high-fidelity imaging turbid tissues and detecting fatty liver.

Lipid droplets (LDs) with own interface architecture not only play crucial roles in protecting cell from lipotoxicity and lipoapoptosis but also closely relate with many diseases such as fatty liver and diabetes. Thus, as one of important applied biomaterials, fluorescent probes with ultrahigh selectivity for in-situ and high-fidelity imaging LDs in living cells and tissues are critical to elucidate relevant physiological and pathological events as well as detect related diseases. However, available LDs probes only utilizing their waterless neutral cores but ignoring the unique phospholipid monolayer interfaces exhibit low selectivity. Particularly, current probes cannot discriminate neutral cores of LDs from intracellular other lipophilic microenvironments, so that extensively cloud-like background fluorescence diffusing in cytoplasm, which severely limited their applications. Herein, in order to design LDs probes with ultrahigh selectivity, the exceptionally interfacial architecture of LDs is considered adequately and thus an interface-targeting strategy is proposed for the first time. According to the novel strategy, we have developed two amphipathic fluorescent probes (N-Cy and N-Py) by introducing different cations into a lipophilic fluorophore (NBD). Consequently, their cationic moiety precisely locates the interfaces through electrostatic interaction and simultaneously NBD entirely embeds into the waterless core via hydrophobic interaction. Thus high-fidelity and background-free fluorescence imaging of LDs is expectably realized in living cells in-situ. Moreover, LDs in turbid tissues like skeletal muscle slices have been clearly imaged (up to 82 μm depth) in two-photon microscope. Importantly, using N-Cy, we not only intuitively monitored the variations of LDs in number, size and morphology, but also clearly revealed their abnormity in hepatic tissues resulted from fatty liver. Therefore, these unique probes provide excellent imaging tools for elucidating LDs-related physiological and pathological processes, and the interface-targeting strategy possesses universal significance for designing probes with ultrahigh selectivity.