Multiplexing immunofluorescence allows researchers to stain a single sample with multiple primary antibodies originating from the same species, even if they have identical isotype. Staining can, e.g., be performed with multiple monoclonal mouse IgG1 kappa primary antibodies or with multiple polyclonal antibodies raised in rabbit at the same time.
All secondary FluoTag-X2 reagents offered by NanoTag are based on monovalent single-domain antibodies (“nanobodies”) carrying two fluorophores each. They are supplied as solutions containing 5 µM nanobody (10 µM fluorophore). You can download a detailed protocol here.