The invention provides a method for preparing an expanded biological specimen suitable for microscopic analysis. Expanding the biological sample can be achieved by binding, e.g., anchoring, key biomolecules to a polymer network and swelling, or expanding, the polymer network, thereby moving the biomolecules apart as further described below. As the biomolecules are anchored to the polymer network isotropic expansion of the polymer network retains the spatial orientation of the biomolecules resulting in an expanded, or enlarged, biological specimen.