Evaluation of Redox Peptide Modified Surfaces for Biosensing Applications

Peptides are promising tools for designing sensitive and stable biosensors. For example, the redox self-assembled monolayer (SAM) based on the sequence Fc-Glu-(Ala)₂-Cys-NH₂ was successful evaluated as transducing interface in electrochemical biosensors. The design of such peptides includes: 1) cysteine to bind covalently the peptide to the gold electrode; 2) glutamic acid in N-terminal position to bind the ferrocene (Fc) in the amine group, and the antibody in the δ-carboxyl group, and 3) alanine to form a hydrophobic layer. Herein, we present the solid-phase synthesis of three different peptides with structure Fc-Glu-(X)₂-Cys-NH₂ (X=Ser, Gly or Phe) and the electrochemical behavior of the obtained SAMs. The Gly was chosen because of its smallest side chain, while Ser and Phe present hydroxyl groups (for H-bonds) and aromatic (for π-π interaction), respectively. The synthesis successful of the HPLC purified peptides were confirmed by mass spectroscopy. From cyclic voltammetry and impedance-derived electrochemical capacitance spectroscopy results, all peptides present reversible redox processes, and electron transfer rates (k_ET ) ranging from 17 to 31 s^-1. Since the peptide with Gly residues presented both the highest surface coverage (Γ = 2.6x10^-10 mol/cm²) and electrochemical capacitance (C_µ = 270 µF/cm²) values, it can be potentially applied for biosensors designing.