The development of lignin-derived carbon dots with dual functionality of fluorescence and enzyme-like activity was realized by hydrochloric acid mediated carbon dots modification, and then a ratiometric fluorescence sensing strategy to detect xanthine oxidase activity was constructed. Sodium lignosulfonate (LS) was used as the carbon source and modified lignin carbon dots (CDs) with both fluorescence and peroxidase-like activities were prepared. DFT theoretical calculations and experiments demonstrated that carbonyl, carboxyl, and chloride on the surface of carbon dots were potential active sites to catalyze production of ·OH from HO. Xanthine oxidase generated HO in the process of catalyzing the production of uric acid from the substrate xanthine. The ·OH produced via LS-CDs catalyzed HO oxidized residual o-phenylenediamine (OPD) groups on surface of OPD-CDs to enhance yellow fluorescence, accompanied by blue fluorescence quenching of LS-CDs. The realization of a highly sensitive, highly selective, and visualized ratiometric fluorescence sensing strategy was achieved. The linear range of the established fluorescence sensing system for xanthine oxidase was 0.5–120 U/L with detection limit of 0.13 U/L. The cascade reaction signal transduction improves the designability of sensing method. Finally, the system successfully realized the sensing of xanthine oxidase in serum and cells.

中文翻译：

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新型木质素衍生碳点纳米酶级联放大用于黄嘌呤氧化酶的比率荧光检测和细胞内成像

通过盐酸介导的碳点修饰实现了具有荧光和类酶活性双重功能的木质素碳点的开发，然后构建了检测黄嘌呤氧化酶活性的比率荧光传感策略。以木质素磺酸钠（LS）为碳源，制备了兼具荧光和类过氧化物酶活性的改性木质素碳点（CD）。 DFT理论计算和实验表明，碳点表面的羰基、羧基和氯基是催化H2O生成·OH的潜在活性位点。黄嘌呤氧化酶在催化底物黄嘌呤生成尿酸的过程中产生H2O。 LS-CDs 产生的·OH 催化 H2O 氧化 OPD-CDs 表面残留的邻苯二胺 (OPD) 基团，增强黄色荧光，同时伴随着 LS-CDs 的蓝色荧光猝灭。实现了高灵敏、高选择性、可视化的比率荧光传感策略。所建立的黄嘌呤氧化酶荧光传感系统的线性范围为0.5~120 U/L，检测限为0.13 U/L。级联反应信号转导提高了传感方法的可设计性。最终，该系统成功实现了血清和细胞中黄嘌呤氧化酶的传感。