Although single domain antibodies isolated from antibody libraries derived from gene synthesis and immunized or naïve animals generally exhibit reasonable affinity, it is often desirable to further increase their affinity. Quantitative library sorting by phage display or yeast surface display is used for improving the affinity of single domain antibodies. In particular, we have developed a proprietary DNA mutagenesis technique that is able to create a huge number (e.g. 1010) variants of the parental antibody with defined positions mutated.

http://www.creative-biolabs.com/Nanobody-Affinity-Maturation.html