A Simple Probe for Super-Resolution Imaging of the Endoplasmic Reticulum in Living Cells

Super-resolution imaging of living cells can reveal nanoscopic details of live biological systems. The development of small-molecule fluorophores that allow optimal imaging conditions is the key to enable live-specimen imaging with minimal invasiveness. In this study, we 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). Photophysical experiments carried out in polyvinyl alcohol films revealed that each molecule yields a high number of photons before photodecomposition (80'000 photons), allowing good localization precision (42 +/- 12 nm) in single-molecule localization experiments. Super-resolution imaging employing this photoactivatable probe permitted the visualization of nanoscopic pores within the network of tubules and sheets of the endoplasmic reticulum. We further analyzed this structure in three dimensions to distinguish pores from concave surfaces and built 3D reconstructions of these nanometric tubules and cisternae.