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Llama serum contains both conventional IgG as well as unique forms of antibody that contain only heavy chains
where antigen binding is mediated through a single variable domain. These variable domains can be expressed
recombinantly and are referred to as single domain antibodies (sdAb). SdAb are among the smallest known
naturally derived antigen binding fragments, possess good solubility, thermal stability, and can refold after heat and
chemical denaturation. Llamas were immunized with either BoNT A or B toxoid and phage display libraries
prepared. Single domain antibodies (sdAb) that were able to detect botulinum neurotoxin (BoNT) serotypes A and
B were selected from their respective libraries. Here, the binders obtained by panning the BoNT B library on either
BoNT B toxoid or BoNT B complex toxoid coated plates or BoNT B toxin coupled microspheres are described.
Using these panning methods, we selected for binders that showed specificity for BoNT B. Phage displayed binders
were screened, moved to a protein expression vector and soluble sdAb was produced. Using a Luminex flow
cytometer binders were evaluated in direct binding assays. We have exploited the unique properties of sdAb and
used them as biological recognition elements in immuno-based sensors that can detect BoNT B.
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