NanoTag® selector resins are based on a high-affinity single-domain antibody (sdAb) that is covalently immobilized on 4 % cross-linked agarose beads. The innovative, oriented and selective attachment via a flexible linker guarantees a high accessibility of the sdAbs and largely eliminates batch-to-batch variations. Due to the single-chain nature of sdAbs and their stable and covalent attachment, no leakage of light and heavy chains is observed during elution with SDS sample buffer. Selector resins thus features high affinity and superior capacity, while showing negligible unspecific background. Selector resins are compatible not only with physiological buffers but also with high stringency buffers. Selector resins thus provide great freedom to adjust the binding and washing conditions to the experimental needs.