Homogeneous TR‑FRET employs long‑lived lanthanides (Eu³⁺, Tb³⁺) as donors paired with acceptor dyes.

Following donor excitation, time‑delayed detection is used to avoid short‑lived background fluorescence.

FRET takes place when the donor–acceptor distance is less than 10 nm, causing the acceptor to emit characteristic fluorescence.

The signal intensity is proportional to the strength of the molecular interaction.