10-N-Nonyl acridine orange (NAO) is an acridine orange derivative and is generally used as a fluorescent marker of the inner mitochondrial membrane in whole cells. It is believed to bind to negatively charged phospholipids. NAO accumulation in the cell seems to be related to specific interactions with mitochondrial membrane proteins and/or lipids, such as cardiolipin, and is largely independent of mitochondrial membrane potential.
Staining of mitochondrial membranes with 10-nonyl acridine orange, MitoFluor Green, and MitoTracker Green is affected by mitochondrial membrane potential altering drugs: J. F. Keij, et al.
As the head group forms such compact bicycle structure, the head group area is quite small relative to the big tail region consisting of 4 acyl chains. Based on this special structure, the fluorescent mitochondrial indicator, nonyl acridine orange (NAO) was introduced in 1982,[6] and was later found to target mitochondria by binding to CL. NAO has a very large head and small tail structure which can compensate with cardiolipin’s small head large tail structure, and arrange in a highly ordered way.