Generalized One-Pot Strategy Enabling Different Surface Functionalizations of Carbon Nanodots to Produce Dual Emissions in Alcohol–Water Binary Systems

Fluorescent dual-emission carbon nanodots (DECNDs), which contained two different emitters, the blue emitters (λex = 315 nm, λem = 386 nm) and the yellow emitters (λex = 365 nm, λem = 530 nm), were first and simply synthesized by one-step hydrothermal treatment using ascorbic acid (AA) as a carbon source in alcohol–water binary systems. The two emitters could be easily separated through extraction with chloroform. A series of experiments demonstrated that the alcohol–water binary systems played a vital role in synthesis of DECNDs, and the dual emissions were ascribed to two types of carbon nanodots due to the different modified ligands on their surfaces, such as ascorbic acid capped on the blue emitters and alcohol molecules capped on the yellow emitters. By taking advantage of the unique dual-emission characteristic, some new applications were developed. For instance, on the basis of the independent responses of dual emissions to low pH values, the DECNDs could be used as a reliable and accurate pH sensor in acid medium, and both intensity of a single emission and intensity ratios of dual emissions could be employed to construct calibrations for pH measurement. Besides, the obtained DECNDs also exhibited excellent biocompatibility and low cytotoxicity, suggesting great potential for biomedical applications.