Mitochondria immobilized carbonized polymer dots for ratio-metric tracking mitophagy

Mitophagy is essential for adjusting the homeostasis of mitochondria and real-time monitoring mitophagy process is essential for investigating mitochondrial-related physiology/pathology status. However, most fluorescent probes are focused on organic dyes, while toxicity, water-solubility, and photobleaching issues are required to be addressed. Herein, fluorescent carbonized polymer dots (CPDs) that can visualize the process of mitophagy with ratio-metric mode and are independent of the mitochondria membrane potential have been fabricated for the first time. The CPDs are composed of a crosslinked polymer core and phenanthroline-like structure, which can be firmly immobilized on mitochondria, due to their lipophilic polymer core. Obvious pH-sensitive and ratio-metric fluorescent features within pH 5 and 8 are observed in the CPDs. The pKa of CPDs is determined to be 6.67, which is highly consistent with neutral physiological pH, which can satisfy the requirement of monitoring mitophagy. Subsequently, we have found that the CPDs can be targeted to mitochondria and precisely monitor the pH perturbation during the mitophagy induced by CCCP or rapamycin. Interestingly, the process of CCCP elicited mitophagy relieved by the methyladenine or chloroquine can be also monitored by the CPDs. The acidification of mitochondria at this condition, combined with the rationally designed CPDs may provide a promising direction for investigating the mechanism of mitochondria in some bioprocesses.