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. 2016 Feb 4;16(2):197. doi: 10.3390/s16020197

Scheme 2.

Scheme 2

Principle of the Tb-to-QD FRET immunoassay against PSA. Both QD and Tb AB conjugates (left) are present in the assay solution at a constant concentration. The addition of PSA leads to the formation of [QD-AB]-PSA-[Tb-AB] complexes and a close proximity of Tb and QD, which results in FRET (middle). This assay leads to a typical immunoassay calibration curve, for which the FRET intensity increases (first linearly and then approaching a maximum value when the PSA concentration reaches the concentration of QD-ABs or Tb-ABs and a formation of further FRET- pairs is not possible) with increasing PSA concentration (right).