Spatiotemporally Monitoring Cell Viability through Programmable Mitochondrial Membrane Potential Transformation by Using Fluorescent Carbon Dots

Mitochondria are the powerhouse of the cell, which maintain the metabolism of living cells. Mitochondrial membrane potential (MMP) is the key parameter of mitochondria and represents cellular activity. The programmable MMP transformations, i.e., normal, decrease, and vanishing, are indicative mitochondria healthy/damaged/dead states. Therefore, methods for monitoring MMP are of great importance. In this work, carbon dots responsive to mitochondrial membrane potential (MMP-CDs) are prepared by a simple microwave method. The intracellular distribution of the MMP-CDs is dependent on the mitochondrial membrane potential. Three different spatiotemporally organelle distributions (mitochondria/lysosome/nucleus) of the MMP-CDs indicate three distinct MMP levels (normal/decrease/vanishing), which represent three different cell states (healthy/damaged/dead). The normal cells with high mitochondrial membrane potential causes the MMP-CDs to accumulate in the mitochondria due to the Nernstian effect. The MMP-CDs are released from the mitochondria and transported to the lysosome when cells are in apoptosis with the decreased mitochondrial membrane potential. In dead cells with a vanished mitochondrial membrane potential, the MMP-CDs are collocated with the nucleus due to the affinity with DNA. Thus, various cellular states can be visualized through the different localizations of the MMP-CDs. These MMP-CDs are successfully employed in the detection of autophagy and H 2 O 2 -induced mitochondria and mitochondrial membrane potential changes.