In this final step we can develop desired applications for one or more of the selected nanobodies. A frequently developed application is the ELISA assay. Their small size allows for the selection of nanobodies that recognize smaller domains of the desired target can be selected and development of more accurate ELISAs. One of the possible ELISAs is the sandwich ELISA, for which we can select both the primary and secondary antibodies and ultimately the tertiary antibody with the detection label attached, such as an HRP.
Alternatively, nanobodies can be immobilized for affinity chromatography applications. For example, we can link nanobodies to sepharose beads that are used to load small columns. This is ideal for purification of your own in-house expressed recombinant proteins without the need of generic purification tag. But there is certainly more possible.