Designed ankyrin repeat proteins (DARPins) possess a highly stable, modular, and rigid protein architecture derived from naturally occurring ankyrin repeat motifs. Each individual repeat typically consists of approximately thirty-three amino acids that fold into a helix-turn-helix structural conformation. These modular units stack together in tandem arrays—usually comprising a central N-capping module, two to four internal repeating units, and a C-capping module—to form a stable domain with a conserved hydrophobic core and a highly variable, solvent-accessible surface area that can be engineered to bind specific target molecules with high affinity and precision.