I want to determine whether a transporter is capable of transporting a substrate, and radiolabelled substrates are going poorly. It's very hard to tell whether my membranes are the quality they need to be, how much extra contaminating cell debris there is, and how much the radiolabelled substrate is sticking to these contaminants. Surely, there must be another way to approach this issue that doesn't rely on radioactive substrates.

Alternatively, what can I do to make this cleaner?

I'm attempting to wash off the radiolabelled substrate with another chemical that should outcompete it, and I'm using NADH dehydrogenase activity to correct for it. Still, I'm getting the opposite trend that I should, and even boiled inverted vesicles are showing even higher levels of radioactivity than my allegedly viable IV. Help pls