See Dr. Ibbs comment above! It would help, if you said what you want to do with them.

It is possible to use EM embedding resin to "cover slip" them. Once the resin is hard, you can pull the section off  the slide ---after you have cooled it with liquid N2.  Once off the slide, you can use a number of different stains. However, this approach has limitations due to the resin permeability.  The sections  can then be remounted on a slide without gelatin. So if you want of make one slide with sequential sections (with different stains) it is possible.

If you have put the sections on the slide without any adhesive and you think they will come off in your staining procedure, you should try your technique with several pre- treatments. 1. Fix the sections in formalin (if you can). this gives a bit more strength to the section and it may resist coming off. 2. Use the old chrome alum technique. Instead of floating the sections on pre treated slides, dip the whole section in the solution and let dry in the light. This also helps the sections stay on, but can block staining.

Hope this helps. Good luck

Thank you very much for your response. Sorry I did not give more details before.

Our sections were 4% PFA perfused brain slices of 100 um thickness. The student mounted them on some commercial pre-coated slides (with + charges, apparently). We were trying to stain them with Nissl, but at the stage of water, the sections started peeling off. We try to put them back on the slides, but it ended up being all the sections were somewhat torn when drying up. I also tried to peel them from water and PBS and remount them on our own gelatin-coated slides. They dried up torn as well.

Thank you again for your help!

This tends to be the problem with 100u sections on this type of slide. Much thinner sections would have given less of a problem.

But with sections that thick you can stain them off the slide to begin with.  Then mount them when you are done staining. If not, the above method of chrome alum gelatin can help with the tissue you have, but it is not perfect approach. Also another method, is to coat the very dry sections with a very dilute solution of Nitrocellulose. Then proceed to stain.