pH-Controllable Bioelectrocatalysis Based on Surface Charge and Conformation Switching of Nonelectroactive Protein

Abstract

Lysozyme (Lys), a nonelectroactive protein, was covalently bonded with L-cysteine (L-Cys) selfassembled monolayers (SAMs) on Au electrode to obtain the pH-switchable interface (Lys/L-Cys). Based on the surface charge and conformational switching of Lys at pH 6.19 and 12.13, the Lys/LCys/Au electrode exhibited a pH-sensitive onoff behavior toward the electroactive probe of Fe(CN) 6 3 . As pH was lower or higher than the isoelectronic point (pI 11.0) of Lys, Lys on electrode was positively or negatively charged by the protonation or deprotonation of amino acid residues. Furthermore, protein conformation was reversibly folded or unfolded to the native state and unfolded intermediate accordingly. Consequently, the electrostatic force between Lys and probe of Fe(CN) 6 3 and reversible conformational change of Lys are responsible for the pH-sensitive onoff behavior of Lys/L-Cys/Au interface. Moreover, the switchable properties of Lys/L-Cys/Au electrode were used to realize pH-controlled electrochemical reduction of H 2 O 2 and exhibited high sensitivity for the bioelectrocatalytic reduction of H 2 O 2 . In the linear range of 0.211.2 mM, the response sensitivity was calculated to be 379 A mM 1 cm 2 . The investigations in the mechanism for pH-sensitive behavior and electrocatalysis of the interface suggest that the nonelectroactive Lys/L-Cys film provides potential for fabricating novel switchable electrochemical biosensors and bioelectronic devices.