I'm using the Click-it Cell Reaction Buffer Kit with AHA azide and AlexaFluor 647 alkyne to measure protein synthesis in HeLa cells and I'm having trouble reducing the background. The protocol says to use 1-5 uM Alexa but even with as low as .1 uM the shift from my AHA (-) to AHA (+) cells is very small. I've used the fix/perm/wash methods recommended (4% PFA + .25% triton + 3% BSA) as well as commercial fix/perm/wash buffers in the BD Cytofix/Cytoperm kit and there has been no difference.

Any advice is appreciated.