Alkali-assisted facile and scalable preparation of fluorescent sulfur-doped carbon dots with excellent optical and biological properties from thioctic acid

The preparation of high-performance heteroatom-doped fluorescent carbon dots (CDs) from renewable biomass or biometabolites hold an extensive attention. Here, we report an excess sodium hydroxide (NaOH) assisted method for the preparation of sulfur-doped carbon dots (S-CDs) at lower temperatures by using thioctic acid (TA). Excessive NaOH can promote the thermal decomposition process of thioctic acid in the hydrothermal process, thereby realizing rapid reaction rate (critical time 1 h) and scalable synthesis at low temperature (120 degrees C). The amount of NaOH and the reaction time were identified as the main factors affecting the synthesis, and the reaction of NaOH with disulfide bonds contributed the most to the generation of fluorescent S-CDs. This in-situ sulfur doping process resulted in excellent fluorescence properties, high relative quantum yield of 11.5%, low biotoxicity, good biocompatibility and excellent solubility, etc. In addition, this as-prepared fluorescent SCDs showed excellent concentration dependence on ferric ions (Fe3+) and can achieve high-precision and selective detection. This work may provide a high-efficiency synthesis strategy for S-CDs for biological and detection applications.