pH-homeostasis is crucial for maintaining a living system of cells. Lysosome, a digestive system of cells, contains a number of hydrolytic enzymes which can normally function in a narrow range of acidic pH (4.5–5.5). Abnormal pH in lysosomes leads to lysosomal dysfunction, which results in various diseases such as lysosomal storage disorders, cancer, cardiovascular diseases, and neurodegenerative diseases. We previously reported a series of reduced xanthene fluorophores including fluorescein, rhodol and rhodamine, and discovered a reduced rhodol, Rh–OMe, with a methoxy and a free amino group in a xanthene ring. In this work, a series of novel pH-sensitive fluorescent sensors for monitoring acidic lysosomes was developed by structure-pKa relationship study of Rh–OMe. Rh–OMe derivatives with various substituents in an alkoxy group on xanthene ring were designed and evaluated by the analysis of pH-titration curves and photochemical properties. Reduced rhodol probes with a para-substituted benzyloxy group showed excellent fluorescence transition triggered by acidic pH, and they were successfully applied to in vitro imaging of lysosomes in HepG2 cells.

pH稳态对维持细胞的生存系统至关重要。溶酶体是细胞的消化系统，其中包含许多水解酶，这些水解酶通常可在较弱的酸性pH（4.5-5.5）范围内发挥作用。溶酶体的pH异常会导致溶酶体功能障碍，从而导致多种疾病，例如溶酶体贮积病，癌症，心血管疾病和神经退行性疾病。我们先前报道了一系列还原的x吨荧光团，包括荧光素，Rhodol和若丹明，并发现了还原的Rhodol Rh-OMe，在x吨环中具有甲氧基和游离氨基。在这项工作中，通过Rh-OMe的结构-pKa关系研究，开发了一系列用于监测酸性溶酶体的新型pH敏感荧光传感器。通过分析pH滴定曲线和光化学性质，设计和评估了x吨环烷氧基上具有各种取代基的Rh–OMe衍生物。具有对位取代苄氧基的还原型rhodol探针显示出由酸性pH触发的出色荧光转变，并且已成功地应用于HepG2细胞中溶酶体的体外成像。