Section16:Uniformity Plate

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To test instrument detector variation, a uniformity plate with the same level of radioactivity in all wells is generated. The counting results are analyzed for each detector as well as across the plate by columns and rows to determine if any detectors require adjustment. Periodic counting of a uniformity plate (called a Performance Check) can identify detector drift or other instrument problems. This procedure can be performed regardless of the instrument type or the number of detectors.

Since many assays are performed in a concentration response mode, a gradient signal across the plate is an expected result. An example of how Performance Check using a uniformity plate can assist in reducing instrument variability is shown below:

To generate a 96-well microplate for [¹²⁵I] SPA beads, labeled beads are prepared using WGA beads, [¹²⁵I]-ligand and receptor membranes. A brief procedure is described below.

Add receptor membranes, [¹²⁵I]-ligand and WGA SPA beads in an appropriate buffer in a single tube. After an incubation time (consistent with the biological system), add 200 µl of diluted bead mixture per well using a 12-channel pipette. Change tips for each row. Allow beads to settle overnight (stable counting conditions) or centrifuge if the receptor/ligand interaction is not stable. Count radioactivity in Microbeta (use clear bottom plate) or TopCount (use opaque bottom plate).

Results for a typical read using a clear bottom plate and a 12-detector Microbeta Trilux are shown on the following page. The relative efficiency between all 12 detectors is >95%.