Designing of nucleolus-targeted carbon dots by controlling the carbon and nitrogen sources

Nucleolus selective imaging can reveal the nucleolus structure and characters of cells in different states, and is considered critical in early disease diagnosis and treatment, and in designing targeted delivery systems. In this paper, we analyzed the factors affecting the nucleolus targeting properties of carbon dots by preparing a variety of carbon dots. Only carbon dots with m-phenylenediamine as the carbon source can specifically target the nucleolus. Meanwhile, the nitrogen content in the carbon dots also affects their targeting properties to the nucleolus. The molar ratio of m-phenylenediamine (carbon source) to l-aspartic acid (nitrogen source) was changed to control the nitrogen content in the carbon dots, and the carbon dots had the best nucleolus targeting and imaging effect when the molar ratio was 1:0.5 (carbon: nitrogen). Additionally, binding of carbon dots to RNA in the nucleolus has been demonstrated by digestion experiments, and their cellular internalization is temperature, ATP, and micropinocytosis dependent. Our results provide ideas and methods for the design of nucleolus-targeted carbon dots.