Super-resoln. imaging of living cells can reveal nanoscopic details of live biol. systems. The development of small-mol. fluorophores that allow optimal imaging conditions is the key to enable live-specimen imaging with minimal invasiveness. The authors report a simple and non-toxic rhodamine-based diazoindanone probe compatible with direct stochastic optical reconstruction microscopy (d-STORM). Co-localization studies performed in human cervical cancer (HeLa) cells indicated that this probe targets the endoplasmic reticulum (ER). Photophys. expts. carried out in polyvinyl alc. films revealed that each mol. yields a high no. of photons before photodecompn. (80'000 photons), allowing good localization precision (42 ± 12 nm) in single-mol. localization expts. Super-resoln. imaging employing this photoactivatable probe permitted the visualization of nanoscopic pores within the network of tubules and sheets of the endoplasmic reticulum. The authors further analyzed this structure in three dimensions to distinguish pores from concave surfaces and built 3D reconstructions of these nanometric tubules and cisternae.