Thanks for the tips. I do use RNAse free stuff mostly working in a biological safety cabinet, and everything I use is one-time use sterile equipment etc. Some of the suggestions I've tried, but using EDTA increases the lipid nanoparticle size which isn't desirable. I need to balance the properties of the particle with the RNA integrity. At the moment I have a good method of stabilising the particles, but if I change something like the pH to stabilise the mRNA, the particle grows or doesn't encapsulate the mRNA.
My samples are stored at -80, -20 and accelerated deg at 2-8C, but trying to get it stable at -20. I also lyophilise the samples but they are less stable.