Design of Dendritic Zwitterionic Oligopeptides with Superior Antifouling Capability for Electrochemical Detection in Diverse Complex Biological Fluids

Electrochemical biosensors are often compromised by nonspecific adsorption in complex biological fluids. Although zwitterionic peptides (ZIPs) demonstrate excellent antifouling properties through the formation of hydration layers, conventional linear ZIPs face a severe limitation: unstable hydration under dynamic complex conditions due to a longer dipole moment, local charge, and conformational flexibility. To address these limitations, we designed a novel dendritic zwitterionic oligopeptide with a three-dimensional branched architecture by alternating glutamic acid (E) and lysine (K) residues around a cysteine (C) core [e.g., EK(E)CE(K)K] according to traditional linear ZIPs (CEKEKEK). Comparative experiments revealed that the dendritic ZIPs exhibited significantly enhanced hydrophilicity and antifouling performances over linear CEKEKEK when exposed to human saliva, sweat, and even in blood. Molecular dynamics simulations revealed that the flexible CEKEKEK oligopeptide, with 2 intramolecular hydrogen bonds between hydrophilic groups distributed at termini of the polypeptide, exposing the peptide bond at the middle part, undergoes local charge and an uneven and unstable hydrated layer. However, the dendritic EK(E)CE(K)K oligopeptides formed 8 intramolecular hydrogen bonds, lowering the dipole moment between -COOH and -NH₂ groups with maintaining high conformational stability, which helps form a stronger hydration layer under physiological conditions than the linear CEKEKEK. Leveraging this design, we successfully developed an antifouling electrochemical biosensor based on this dendritic ZIPs as example for detecting C-reactive protein in saliva, achieving detection accuracy consistent with the ELISA method. The dendritic design provides a strategy for enhancing the contamination resistance ability and offers a significant advancement for next-generation biosensors in complex biological environments.