Which of the following stains can be utilized to characterize the state of mitochondria?

Rhodamine-123 is a fluorescent dye that selectively accumulates in active mitochondria due to their potential-dependent uptake mechanism. This characteristic makes it particularly useful for assessing mitochondrial function and viability. When used, the dye emits fluorescence in living cells, allowing researchers to visualize and evaluate the state of mitochondria under different conditions.

The selective accumulation of Rhodamine-123 in mitochondria indicates that it can serve as a reliable indicator of mitochondrial membrane potential—a key indicator of mitochondrial health and function. Therefore, changes in the fluorescence intensity of Rhodamine-123 can provide insights into mitochondrial energy production and overall cell viability.

In contrast, while acridine orange, ethidium homodimer-1, and calcein-AM may also apply to cellular and cytoplasmic assessment, they are either more broadly used for other cellular compartments or conditions rather than specifically targeting the state of mitochondria. Thus, Rhodamine-123 stands out as a specific and effective choice for characterizing mitochondrial health.