Ratiometric near-infrared (NIR) fluorescent probes are attractive tools for bioimaging applications. Although many fluorescent probes have been developed for detection of the biologically important cysteine (Cys), ratiometric NIR fluorescent probes for Cys are very rare, particularly those with significant fluorescence enhancement in the NIR region. In this work, a new ratiometric NIR fluorescent probe with significant NIR fluorescent turn-on changes was reported for rapid, colorimetric and ratiometric fluorescent detection of Cys. This probe is able to detect Cys in aqueous solution under mild conditions, with high selectivity and sensitivity for Cys over various analytes including the similar structured homocysteine (Hcy) and glutathione (GSH). The detection limit of this probe for Cys was found to be as low as 0.2 μM, which is far below the normal content of Cys (30–200 μM) in cells. Besides the excellent sensing properties, this probe shows low cytotoxicity and can be conveniently applied to image intracellular Cys in living cells, indicating it is a promising tool for biological applications.

比率式近红外（NIR）荧光探针是用于生物成像应用的有吸引力的工具。尽管已开发出许多荧光探针来检测生物学上重要的半胱氨酸（Cys），但用于Cys的比例NIR荧光探针非常少见，尤其是在NIR区域具有明显荧光增强作用的探针。在这项工作中，据报道一种具有显着NIR荧光开启变化的新型比例NIR荧光探针可用于Cys的快速，比色和比例荧光检测。该探针能够在温和条件下检测水溶液中的Cys，对Cys的选择性和灵敏度高于各种分析物，包括相似的结构同型半胱氨酸（Hcy）和谷胱甘肽（GSH）。发现该探针对Cys的检出限低至0.2μM，这远远低于细胞中Cys（30–200μM）的正常含量。除了出色的感测特性外，该探针还显示出低细胞毒性，可以方便地应用于活细胞中细胞内Cys的成像，这表明它是用于生物学应用的有前途的工具。