Tris/glycine buffer is not compatible with Bio-Plex cytokine assays. The cytokines in both the samples and standards already generally exist in low concentrations. Low-pH Tris/glycine buffer degrades cytokines so they are no longer in native form. Our antibodies are directed to native, non-denatured proteins, so you will get a weak signal if using Tris/glycine buffer.
In addition, if you dilute the standards in Tris/glycine buffer without using bovine serum albumin (BSA) or other carrier proteins, the proteins in the standards can stick to the walls of the wells, resulting in a low signal.