Esterase is primarily distributed in the endoplasmic reticulum (ER) and often overexpressed in cancer cells. Therefore, the detection of esterase in ER is significant for monitoring the metabolic process of various esters and evaluating the efficacy of chemotherapeutic prodrugs. However, only few fluorescent probes can detect esterase in the ER due to the lack of ER-specificity. More seriously, these probes are often limited by low pearson’s colocalization coefficient and one single wavelength emission. To solve those problems, an ER-specific ratiometric fluorescent probe (ER-EST) is designed for detecting esterase in living cells. The ER-EST shows a ratiometric and red-shifted emission (125 nm) from 435 to 560 nm after hydrolysis by esterase. The fluorescence intensity ratio of ER-EST displays quantitative response to the esterase activity (0–0.5 U/mL) with low detection limit of 1.8 × 10^-4 U/mL. Importantly, the ER-EST with good biocompatibility and excellent ER-targeted ability was successfully employed to ratiometric image the endogenous endoplasmic reticulum esterase in living cells.

酯酶主要分布在内质网 (ER) 中，并且通常在癌细胞中过度表达。因此，ER中酯酶的检测对于监测各种酯的代谢过程和评估化疗前药的疗效具有重要意义。然而，由于缺乏 ER 特异性，只有少数荧光探针可以检测 ER 中的酯酶。更严重的是，这些探针通常受到低皮尔逊共定位系数和单一波长发射的限制。为了解决这些问题， ER 特异性比率荧光探针 ( ER-EST ) 被设计用于检测活细胞中的酯酶。ER -EST显示在酯酶水解后从 435 到 560 nm 的比率和红移发射 (125 nm)。ER-EST的荧光强度比显示对酯酶活性 (0–0.5 U/mL) 的定量响应，检测限低至 1.8 × 10 ^-4 U/mL。重要的是，具有良好生物相容性和出色 ER 靶向能力的ER-EST已成功用于对活细胞中的内源性内质网酯酶进行比例成像。