See the Unseen: Red‐Emissive Carbon Dots for Visualizing the Nucleolar Structures in Two Model Animals and In Vivo Drug Toxicity

Abstract Nucleolus, which participates in many crucial cellular activities, is an ideal target for evaluating the state of a cell or an organism. Here, bright red‐emissive carbon dots (termed CPCDs) with excitation‐independent/polarity‐dependent fluorescence emission are synthesized by a one‐step hydrothermal reaction between congo red and p ‐phenylenediamine. The CPCDs can achieve wash‐free, real‐time, long‐term, and high‐quality nucleolus imaging in live cells, as well as in vivo imaging of two common model animals—zebrafish and Caenorhabditis elegans ( C . elegans ). Strikingly, CPCDs realize the nucleolus imaging of organs/flowing blood cells in zebrafish at a cellular level for the first time, and the superb nucleolus imaging of C . elegans suggests that the germ cells in the spermatheca probably have no intact nuclei. These previously unachieved imaging results of the cells/tissues/organs may guide the zebrafish‐related studies and benefit the research of C . elegans development. More importantly, a novel strategy based on CPCDs for in vivo toxicity evaluation of materials/drugs (e.g., Ag + ), which can visualize the otherwise unseen injuries in zebrafish, is developed. In conclusion, the CPCDs represent a robust tool for visualizing the structures and dynamic behaviors of live zebrafish and C . elegans , and may find important applications in cell biology and toxicology.