Spatial resolution with the benchmark dyes and the four novel red dyes in the focal plane of a STED microscope. The insert panels show the individual 'point-like' raw data spots (most likely antibody clusters) from which the shown line profiles were extracted, indicating the spatial resolution in the focal plane. The solid lines represent optimal Gaussian fit curves. The novel STAR dyes provides a focal plane resolution of <25 nm (in raw data). Scale bars, 500 nm.