High quantum yield orange-emission carbon dots for rapid mitochondrial-targeted and dynamic tracking in apoptosis and autophagy

Monitoring dynamic changes in mitochondrial morphology is essential for studying specific diseases. In this paper, orange-emitting carbon dots (OM-CDs) which had a high quantum yield (55.53 % in water and 77.26 % in ethanol) and could specifically target to mitochondria for long-term dynamic tracking, were successfully prepared using a simple solvothermal method. OM-CDs contained lipophilic cationic rhodamine fluorophores, which possessed a positive charge capable of electrostatically interacting with the negatively charged mitochondria. OM-CDs emitted strong fluorescence at 588 nm from the Rhodamine fluorophores excited by the optimal excitation wavelength of 572 nm. The OM-CDs’ fluorescence intensity was almost unaffected by different ions and amino acids, pH, polarity and viscosity of solvents, showing excellent photostability and resistance to interference. OM-CDs rapidly locked onto mitochondria within 10 min, with a Pearson's correlation coefficient (PCC) of 0.92, showing a good match with mitochondria. OM-CDs accurately tracked mitochondrial morphological changes during apoptosis induced by 50 μM H₂O₂ and mitochondrial autophagy induced by 10 μM rapamycin over a period of 20 min. The prepared OM-CDs have significant potential for applications in diagnostic and therapeutic strategies for mitochondria-related diseases.