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Accurate detection of carboxylesterases (CEs) plays a crucial role in various disease physiological processes and ester-containing drug metabolism. However, the reported near-infrared (NIR) fluorescent probes with short Stokes shift (<70 nm) limited their application of tracking CEs activity in complex bio-systems. Herein, a new "turn-on" NIR fluorescent probe for CEs detection (termed as CE-1) was developed based on dicyanoisophorone with large Stokes shift over 100 nm for the first time. The probe CE-1 (λex/em = 535/665 nm) featured low cytotoxicity and high sensitivity (detection limit of 2.76 × 10−3 U/mL). Moreover, the CE-1 was successfully used to detect the level changes of CEs under drug-induced modulation in cell imaging, and real-time monitor the activity of CEs in mice models for biological imaging. Notably, these results indicate that the probe CE-1 can be applied for imaging and monitoring endogenous CEs in living systems. We believe that the probe CE-1 will be applied as a potential indicator of CEs for the clinical diagnosis of CEs-related diseases and rational use of drugs. [Display omitted] • A new dicyanoisophorone-based NIR fluorescent probe CE-1 was developed for the detection of carboxylesterases. • Probe CE-1 emitted in the red region with an excellent Stokes shift (130 nm). • Probe CE-1 exhibited high selectivity and sensitivity towards carboxylesterases (LOD: 2.76 × 10−3 U/mL). • Probe CE-1 was successfully applied to detect carboxylesterases in living cells and mice. [ABSTRACT FROM AUTHOR]

• A simple near-infrared fluorescence probe based on dicyanoisophorone was synthesized. • This probe exhibited excellent specificity in the detection of N 2 H 4 over other amino compounds. • This probe showed excellent response performance to N 2 H 4 through distinct fluorescence enhancement. • This probe was applicable for N 2 H 4 detection in living cells and real water samples. With the widespread use of N 2 H 4 , it brings potential risks to human health. In order to determine N 2 H 4 effectively in both environment and living systems, a simple near-infrared fluorescence probe was prepared for the specific response of N 2 H 4 based on the intramolecular charge transfer (ICT) mechanism. This probe provided a "turn on" fluorescence response to N 2 H 4 with characteristics including high selectivity, rapid response (within 1 min), low cytotoxicity, and low detection limit (0.022 μM). In addition, it can be used to expediently trace N 2 H 4 in HepG2 cells and water samples. Thus, Probe 1 is a promising tool to identify the level of N 2 H 4. [ABSTRACT FROM AUTHOR]