Single molecules that exhibit narrow optical transitions at cryogenic temperatures can be used as local electric-field sensors. We derive the single charge sensitivity of aromatic organic dye molecules, based on first principles. Through numerical mo
deling, we demonstrate that by using currently available technologies it is possible to optically detect charging events in a granular network with a sensitivity better than $10^{-5}e/sqrt{textrm{Hz}}$ and track positions of multiple electrons, simultaneously, with nanometer spatial resolution. Our results pave the way for minimally-invasive optical inspection of electronic and spintronic nanodevices and building hybrid optoelectronic interfaces that function at both single-photon and single-electron levels.
