Light Sci. Applications 5, e16134 (2016)

The axial resolution of confocal microscopy techniques can be enhanced to reach the super-resolution regime by simply replacing the standard microscope slide on which the specimen is mounted with a mirror. That's the finding of Xusan Yang and co-workers, who call their scheme mirror-enhanced axial-narrowing super-resolution (MEANS) microscopy. The approach works because the addition of a mirror behind the specimen leads to interference between the excitation and its reflection from the mirror, which then results in a narrowed point spread function. Yang et al. combined the approach with stimulated emission depletion (STED) microscopy to improve axial resolution by a factor of six (to 110 nm) and lateral resolution by a factor of two (to 19 nm) and to probe nuclear pore complexes and viral filaments. A benefit of the approach is that the improvement in resolution comes without the need to increase laser power, which could damage sensitive biological samples. The team says that MEANS is compatible with various confocal microscopy schemes including two-photon imaging, spinning disk microscopy and laser scanning.