I am trying to fix the nucleosomes by formaldehyde. The idea is to make the nucleosomes stable at high salt concentration and temperature by crosslinking DNA with Histone octamer. We have nucleosomes at 100ng/ul and add the formaldehyde to this solution at a final concentration of 1%. Let it incubate for 45min and check the sample on 6% native PAGE in 0.4X TBE at 90V for 90min. The control sample which is only nucleosomes runs properly at 450bp as expected but the formaldehyde fixed nucleosomes donot appear in the gel image. I think the nucleosomes got aggregated in the solution and not running through the gel. The mononucleosomes are purchased from EpiCypher which contains 146bp DNA and Histone octamer which makes it around 200kDa. Please let me know if you have any ideas to fix the nucleosomes and the possible issues with my experiment.