By placing fluorescent nanoparticles above a mirror, the microscopy image depends sensitively on the axial position of the nanoparticle, which can be used for a sub-diffraction limited localization. A numerical simulation with JCMsuite shows that the localization sensitivity is an effect of the single emitter's interference with its own mirror image.
Y. Liu, et al. Axial localization and tracking of self-interference nanoparticles by lateral point spread functions. Nat. Commun., 12, 2019 (2021).