A dual-response near-infrared-emitting fluorescent probe for the evaluation of liver disease-related drugs and multi-level monitoring of lipid droplet abnormalities.

The viscosity and polarity of lipid droplets (LDs) are two crucial physical parameters in their microenvironment. They act as "regulators" of the LDs functions, jointly determining the metabolic activity, stability of LDs, and their roles in cellular stress. Any abnormal change in any one of these indicators can directly affect the metabolic health and fate of cells. Therefore, developing analytical tools that can simultaneously and in real-time monitor the dynamic changes of both of these factors is of crucial significance for revealing the mechanisms of LDs-related metabolic diseases. Based on the triphenylamine structural unit containing ether oxygen chains, through side-chain modification and molecular conformational regulation, five fluorescent dyes (TPAO1-TPAO5) featuring D-π-A or D-π-A-D configurations were successfully designed and synthesized. This family of probes all exhibited excellent photostability and interference performance and are suitable for imaging requirements in complex biological environments. By precisely regulating the balance between intramolecular charge transfer and twisted Intramolecular charge transfer distortion, TPAO1 and TPAO4 exhibited unique dual-response characteristics in terms of polarity and viscosity sensing. Notably, TPAO1, TPAO2 and TPAO5 all exhibited emission maxima above 650 nm, with TPAO1 reaching 715 nm, yielding outstanding near-infrared (NIR) emission characteristics. Moreover, TPAO1 stands out among a wide variety of molecules due to its broad viscosity detection range, suitable lipophilicity, excellent LDs targeting, and high signal-to-noise imaging without water washing. Furthermore, combined with its dual sensitivity to the polarity and viscosity of the microenvironment, this probe could dynamically reflect the metabolic changes in abnormal cells from multiple aspects such as the number, size and fluorescence intensity of LDs, providing multi-angle quantitative evidence for the identification of pathological states, and significantly enhancing the reliability and information dimension of the detection. Thanks to the probe's outstanding ability to image LDs, this study further used the dynamic changes in the number of LDs as a quantitative indicator to systematically evaluate the efficacy of various liver disease treatment drugs (including DGAT1 inhibitors, statins, and antibiotics, etc.), providing an important visual analysis tool and decision-making basis for drug screening and mechanism research. In an in-depth in-vivo evaluation, TPAO1 successfully achieved high-contrast in-vivo imaging in mice model induced by Lipopolysaccharides (LPS) and nystatin (Nys), further validating its outstanding performance in practical biological systems. In conclusion, the successful development of TPAO1 not only provides a powerful research tool for the exploration of LD biology and the evaluation of drug efficacy, but also builds a crucial technological bridge for the clinical transition from molecular imaging to precision diagnostics of diseases.