Labelling

Yes, there are several non-covalent labels that will work examples that has been applied in the past are: - HIS Lite™ OG488-Tris NTA-Ni Complex against the His-tag. - Single domain antibodies against the ALFA-tag. - As well as nanobodies specific for your protein of interest.

No, over-labeling will have no impact on the sizing measurement using Fida. However, mind that for all technologies that rely on labelling to detect interactions over-labelling risks putting a label in or nearby the binding site inhibiting the binding due to stearic hindrance.

An unconjugated label is a much smaller size than a label conjugated to a biomolecule. In FIDA one can identify multiple species and their relative abundance. This is the feature used to give labeling quality.