Expansion microscopy through mechanical force.

Abstract

In biophysics interesting phenomena take place during the interaction between biological molecules on the order of nanometers. Optical super-resolution imaging techniques surpass the diffraction limit of light enabling higher resolutions to study these phenomenon. However, super-resolution techniques usually require expensive equipment. Expansion microscopy (ExM) is a sample preparation method that facilitates super-resolution imaging by leveraging osmotic forces to physically separate features smaller than the diffraction limit of light. ExM is cheaper than and compatible with other super-resolution methods to reach the nanoscale. Currently, ExM commonly produces 4.5X linear expansion and 20X has been achieved using successive expansion steps, but this can result in fragmentation of the biological sample. Allowing the gel to absorb water to expand is also as low process. To overcome the fragmentation and time issues, here, we use a highly stretchable cross-linked polymer gel and a mechanical stretcher device to achieve similar 20X linear expansion in minutes. Since we do not rely on osmotic forces for the expansion, this method is more compatible with other techniques which are incompatible with excess water. We demonstrate our expansion microscopy method by imaging MOSE cells at 50 nm resolution. We establish mechanical force expansion microscopy as a viable sample preparation method with the same advantages as ExM while being much faster. This will also allow researchers to study time sensitive phenomenon.