Antibody fragments and scFv fragments, single chain variable fragments can be E. coli expressed. Fragment peptides for polyclonals give monoclonal like antibodies as the epitope is very small. IgG Fc and(ab)2 fragments are small and stable subunits of the antibody obtained by enzymatic digestion. Complement fragments, bp DNA fragments are common.
Peptides short amino acid chains or epitopes or blocking antagonists. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetra peptides, ... till polypeptides that are long, continuous, and unbranched synthetic peptide chains. These biological oligomers and polymers can be Solid-phase peptide synthesis (SPPS), or in continue produced for custom peptide synthesis projects. The High-efficiency solid phase peptide synthesis (HE-SPPS) is give very low production costs.