SPA scintillation beads are microspheres containing scintillant that emits blue light, making them ideal for use with photomultiplier tube (PMT) counters like the MicroBeta2 or TopCount. These beads come in two core types: yttrium silicate (YSi) and polyvinyltoluene (PVT). PVT beads are plastic, larger, and stay in suspension longer than the crystalline YSi beads. Protein A-coated YSi SPA beads are specifically designed for capturing antibodies in proximity-based radiometric scintillation assays.

Scintillation Proximity Assay (SPA) technology allows for rapid and sensitive analysis of various biological processes, including enzyme and receptor targeting, radioimmunoassays, and molecular interactions. This homogeneous assay utilizes the energy released from radioisotope decay (e.g., 3H, 14C, 33P, 125I) in the form of β-particles or Auger electrons.

When a radiolabeled molecule is close enough to a SPA bead, the emitted particles interact with the scintillant within the bead, producing detectable light. This light signal is then measured by a PMT-based counter. Conversely, if the radioactive molecule is not bound to the bead, the energy of the emitted particles is insufficient to reach the bead, resulting in no light emission. This proximity-based discrimination eliminates the need for physical separation of bound and free radiochemicals, simplifying the assay process. The 500 mg quantity of Protein A-coated YSI SPA beads provides ample material for numerous assays. Yttrium silicate’s crystalline structure contributes to efficient light emission and rapid settling, facilitating quick and accurate results.