Fluorescein diacetate


 * fluorescein (494/518) is formed by intracellular hydrolysis of FDA
 * bacteria can hydrolyze this
 * leaks from cells
 * fluorescein has a relatively high rate of photobleaching
 * pH-sensitive fluorescence ref (pKa ~6.4) that is significantly reduced below pH 7
 * relatively broad fluorescence emission spectrum (not good for multicolor use)