Scintillation-detecting instruments well counters

Conventional scintillation counters such as the Microbeta (Wallac/Perkin Elmer, Turku, Finland) or the TopCount (Packard, Meriden, USA) use photomultiplier detection systems that count 8 or 12 wells at a time, resulting in a readout time of 40 minutes per 384-well microplate. Bialkali photocathodes (Sb-Rb-Cs or Sb-K-Cs) used in standard photomultipliers have a maximum spectral response at about 420 nm, with a quantum efficiency for detection of up to 30%. Thus, the aforementioned instruments are ideally suited for filtration assays and SPA assays with the blue-emitting YSi and PVT beads. 

The move to higher well densities and lower assay volumes has presented significant challenges to instrumentation companies. First, there is the need to detect the results of a particular assay. For example, in the 96-well scintillation proximity assays, the scintillation counter photomultipliers are positioned above... 

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