JC-1 is a fluorescent lipophilic carbocyanine dye used to measure mitochondrial membrane potential.

JC-1 (2.5 μM) exposed to murine L1210 lymphoblasts, can be detected the presence of both cytoplasmic JC-1 monomer and mitochondrial J-aggregates in these cells. JC-1 fluorescence is usually excited by the 488 nm laser wavelength common in flow cytometers[1]. Fluorescent labeling of mitochondria with either JC-1 (1 μg/mL, 15 min), reveals that are distributed irregularly, resulting in regions of high and low mitochondrial content within astrocytes[2]. JC-1 has been shown to interact with α-synuclein at the acidic C-terminal region with a Kd of 2.6 μM. JC-1 itself does not accelerate the protein aggregation of α-synuclein in the absence of iron, insted, it decelerates the aggregation process by extending the lag phase approx[3]. JC-1 is avidly accumulated in sensitive K562 cells where it displays both a green cytoplasmic and red mitochondrial fluorescence. JC-1 is poorly accumulated in resistant K562 cells, which displays only a slight green fluorescence[4].

References:
[1]. A Perelman, et al. JC-1: alternative excitation wavelengths facilitate mitochondrial membrane potential cytometry. Cell Death Dis. 2012 Nov 22;3:e430.
[2]. Vera C. Keil, et al. Ratiometric high-resolution imaging of JC-1 fluorescence reveals the subcellular heterogeneity of astrocytic mitochondria. Pflügers Archiv - European Journal of Physiology. 2011,462(5): 693-708.
[3]. Jung-Ho LEE, In-Hwan LEE, Young-Jun CHOE, et al. Real-time analysis of amyloid fibril formation of α-synuclein using a fibrillation-state-specific fluorescent probe of JC-1. Biochem. J. 2009, 418:311-323.
[4]. Salvioli S, et al. JC-1, but not DiOC6(3) or rhodamine 123, is a reliable fluorescent probe to assess delta psi changes in intact cells: implications for studies on mitochondrial functionality during apoptosis. FEBS Lett. 1997 Jul 7;411(1):77-82.