A group of researchers around Adi Salomon (BINA Nanocenter, Ramat-Gan, Israel) and Martin Oheim (SPPIN) have developed a simple nanometric calibration tool for axial super-resolution imaging. In a pre-print available on biorXiv, they describe a simple, non-invasive, optical technique for simultaneously characterizing the refractive index, thickness, and homogeneity of nanometric transparent layers. In the case of the calibration sample, these layers are made of the biomimetic polymer, My-133-MC, having a refractive index of 1.33, so as to approach the cytosol for biological applications. The technique is based on the detection in the far field and the analysis of supercritical angle fluorescence (SAF), i.e., near-field emission from molecular dipoles located very close to the dielectric interface. Applications to localising FM-dye labelled vesicles in cortical astrocytes are presented.