Oligosaccharide-assisted direct immunosensing of small molecules.

“Sandwich-type” noncompetitive (immunometric) assays allow for high-sensitivity high-throughput macromolecule sensing and determination but cannot be used on small molecules (haptens). Here, we isolated single-chain Fv fragments from a phage-display library, which bound to complexes of particular haptens (vitamin D and A derivatives) with immobilized β-cyclodextrin or β-maltosyl residues, and formed ternary complexes. These scFvs enabled novel “semisandwich-type” immunometric assays of haptens with nanomole-range sensitivities.