Heat denaturation enables multicolor X10-STED microscopy at single-digit nanometer resolution

Expansion microscopy (ExM) improves imaging quality by physically enlarging the biological specimens. In principle, combining a large expansion factor with optical super-resolution should provide extremely high imaging precision. However, large expansion factors imply that the expanded specimens are dim and are therefore poorly suited for optical super-resolution. To solve this problem, we present a protocol that ensures the 10-fold expansion of the samples through high-temperature homogenization (X10ht). The resulting gels exhibited relatively high fluorescence intensity, enabling the sample analysis by multicolor stimulated emission depletion (STED) microscopy, for a final resolution of 6-8 nm. X10ht offers a more thorough homogenization than previous X10 protocols based on enzymatic digestion, and thereby enables the expansion of thick samples. The better epitope preservation also enables the use of nanobodies as labeling probes and the implementation of post-expansion signal amplification. We conclude that X10ht is a promising tool for nanoscale resolution in biological samples.