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Choosing Component Concentrations for FCS Assays

When choosing the concentration of each of the components in your FCS assay sample, the following properties should be considered.

  • Probe Affinity: Probe and target concentrations should be in the optimum range at which biological or chemical interactions occur.
  • Dye Concentration:The QuantumXpert FCS Spectrometer is intended to measure fluorescent dye concentrations from ~50 pM to ~50nM. The number of dye molecules per probe times the concentration of the probe should fall within these boundaries. Specific activity (dyes per probe) can be adjusted so that the probe concentration can be well outside of the 50pM - 50nM boundaries.
  • Aggregation Susceptibility: Many probes, and also fluorescent dyes, will aggregate at high concentrations.