When one of the two interacting partners is a peptide, fluorescence anisotropy can be used to set-up an interaction assay.
This technique is cost effective and very robust.

FP (Fluorescence polarization) interaction assay principle.
The binding of a fluorophore-labeled peptide (e.g. FITC, rhodamine,…)
to a protein results in the decrease of peptide rotation and hence
a measurable increase in polarization upon excitation
with polarized light.