What are the limitations of using ANEP dyes in membrane potential activity analysis?

ANEP dyes are common fluorescent dyes that respond to electrical potential changes. They are ultra fast-responding, and can provide millisecond response time.  This dye method, however, suffers from a number of drawbacks, including a weak signal-to-noise ratio. Additionally, the magnitude of their potential-dependent fluorescence changes frequently, as this measurement is dependent upon membrane potential (MP), which can make analysis and true quantification tricky.