To quantitate lumenal chemistry, my lab developed a DNA-based reporter technology coupled with image analysis methods to derive chemical heat-maps of organelles by fluorescently imaging lumenal ions or reactive species in living systems. This technology can now be used for discovery biology or biomedical applications by interrogating organelles of cells in culture, in live multicellular organisms in cells obtained from blood or skin biopsies from human patients. We recently solved a thirty-year problem in molecular sensing by mapping lumenal calcium in acidic organelles and in doing so, identified the first example of a protein that facilitates lysosomal Ca2+ import in the animal kingdom. We have used a fluorescent DNA-based reporter of absolute membrane potential to measure the previously unknown membrane potentials of different organelles in situ in live cells. I will close with a discussion on what it would take to develop an electrochemical model for every organelle membrane, thereby enabling an exploration of the genesis and function of organellar electrochemical gradients.