Is there a method to alter Refractive index of cell membranes?

try soething like disodium metaphosphate or hexametaphosphate. Get some bags of dry pack and hexametaphosphate soaked SCALLOPS and thin section them and see what you gt.

We used to use bromoform but thats a bit toxic fo longer scope work

@farmerman
Thanks for your reply. Can you share some references or tell me if treatment with bromoform limits its localization to cell membranes? I am imagining that soaking the sample in it will cause uniform distribution across the entire tissue. My objective is to increase the contrast in the refractive indices of cell membranes and surrounding material (eg. cytoplasm).

Im not sure because we would use it as a surface treatment and allow it to permeate the layer. Our samples were microtomed and miked after thawing, Then the Bromoform was added and the RI difference was , say 1.27 before and s.7(something) after treatment.

Im assumig these are not in vivo??

Thanks again for the clarification. I will give these a try.
You are right, I also section the samples in microtome as you do.