Why do you want to use a heated blade? Do you have access to a cryostat?

We have used cold (placed inside a cryostat) needles to obtain small areas of tissue. Depending in the inner diameter of the needle you can obtain 1-2 square millimeters. You can then flush (liquid or air) the needles inside a micro tube for processing.

I don't have any idea what could actually happen to the proteins in the case you are describing. I think the way to go is avoiding the problem of heating the proteins from the beginning.

My guess is that the proteins right along the slice will be heated denatured to some degree. However, people have used microwaved brains to quantify proteins by Western blot. Hence, I doubt there we be an effect on an ELISA type analysis paradigm. However, this is a hunch based upon the literature that I know, which only indirectly addresses your question.

Thanks to all for your time and expertise. I am looking to take a 50mg piece of tissue. I do have access to a cryostat but I'm not sure if this is suitable for the logistics and size of the piece I'll need to take. I still may go ahead with this idea - if microwaved proteins can yield Western results...the other option is just to cut into the frozen tissue and try to keep track of how the pieces fit together.

You generally want to keep the sample cold to prevent protein degradation. I assume you will be lysing the tissue sample in a buffer containing protease inhibitors. Depending on the type of ELISA denaturing proteins may not be a problem but you don't want digested proteins.