Ultrabright Carbon Dots as an Emerging Fluorescent Probe for Multivalent Labeling and Highly Sensitive Detection of Extracellular Vesicles

Extracellular vesicles (EVs) play an important role in many physiological processes, and surface labeling is essential for the research and application of EVs. Fluorescence probes provide a sensitive and visual tool for EV labeling and imaging; however, most of them suffer from some native shortcomings, e.g., false positives caused by the aggregation of hydrophobic organic dyes and membrane destruction in inorganic phosphor labeling. To resolve these issues, in this work, we presented an emerging fluorescent probe, i.e., cholesteryl-modified ultrabright green emissive carbon dots (Chol-GCDs), for multivalent labeling and further highly sensitive detection of EVs. GCDs revealed a high quantum yield (65%), abundant amino groups, and good water solubility. Through a covalent linking, cholesteryl was efficiently modified on the surface of CDs, achieving the construction of a fluorescence probe, i.e., Chol-GCDs, for EV recognition. Chol-GCDs have shown great potential for multivalent and stable EV labeling due to their advantages of plentiful grafting of cholesteryl, ultrasmall size, water solubility, and good tolerance to photobleaching. Thereafter, a sandwich-model fluorescence detection platform (96-well plates) for EVs was constructed. This platform enabled quantitative EV detection over a wide range from 10³ to 10⁶ particles/mL and demonstrated good analytical performance in biological samples such as serum and cell culture supernatants. This work provided a promising and competitive fluorescence label for EV labeling and would open an opportunity to exploit a versatile platform for the research and applications relevant with EVs.