Near-infrared (NIR) fluorescence imaging technique is garnering increasing research attention due to various advantages. However, most NIR fluorescent probes still suffer from a false signals problem owing to their instability in real application. Especially in a pathological environment, many NIR probes can be easily destroyed due to the excessive generation of highly reactive species and causing a distorted false signal. Herein, we proposed an approach for developing a new stable NIR dye platform with an optically tunable group to eliminate false signals using the combination of dyes screening and rational design strategy. The conception is validated by the construction of two high-fidelity NIR fluorescent probes (NIR-LAP and NIR-ONOO − ) sensing leucine aminopeptidase (LAP) and peroxynitrite (ONOO − ), the markers of hepatotoxicity. These probes (NIR-LAP and NIR-ONOO − ) were demonstrated to sensitively and accurately monitor LAP and ONOO − (detection limit: 80 mU/L for LAP and 90 nM for ONOO − ), thereby allowing one to precisely evaluate drug-induced hepatotoxicity. In addition, based on the fluctuation of LAP, the therapeutic efficacy of six hepatoprotective medicines for acetaminophen-induced hepatotoxicity was analyzed in vivo. We anticipate the high-fidelity NIR dye platform with an optically tunable group could provide a convenient and efficient tool for the development of future probes applied in the pathological environment.

The need for detecting and labelling environmentally and biologically important analytes has driven considerable research efforts in developing fluorescent probes. During the sensing process, molecular motions (i.e., molecular rotations or vibrations) of a flexible fluorescent probe can be significantly altered by its embedding micro-environment or analyte, thereby leading to substantial changes in readout signals. Motion-induced change in emission (MICE) can be utilized as an effective sensing mechanism. However, in comparison to the well-understood sensing mechanisms, such as photo-induced electron transfer (PET), intramolecular charge transfer (ICT), aggregation-induced emission (AIE) and disaggregation-induced emission (DIE), MICE has not been systematically discussed to date. In this tutorial review, we will summarize the concept and mechanisms of MICE for developing single-molecular fluorescent probes, present unique advantages of MICE based sensors, demonstrate their various applications, and discuss technical challenges in this field. We expect that this review will promote a deeper understanding of MICE and facilitate the development of novel MICE based probes.

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