Nanobody, also known as single-domain antibody (sdAb), is an antibody fragment consisting of a single monomeric variable antibody domain, known as V_HH fragment. Nanobody or sdAb cab be engineered from heavy-chain antibodies found in camelids. Heavy-chain antibodies differ from conventional antibodies in that they lack the light chains of conventional antibodies. Their heavy chains consist in C_H2 and C_H3 domains but not C_H1 domain, which are significantly shorter than conventional antibodies.

Nanobodies, ie V_HH fragments from sdAb, have very different binding characteristics from conventional antibodies, largely owing to an extended loop in their complementarity-determining region 3 (CDR3). Such a feature not only improves the hydrophilicity and stability of nanobody, but also allow nanobodies to bind to buried sites inside a protein that are not accessible to conventional antibodies.

BiCell Scientific Inc’s nanobody development service utilizes the natural immune system of alpaca (Lama pacos) to generate de novo nanobody sequences from hyperimmunized B cells. These nanobody sequences are then cloned into a yeast display library to facilitate screening and discovery of high-affinity nanobodies.