Polydopamine-Functionalized MWCNT–Gold Nanoparticle Composite with Immobilized Heme Protein for Enzymatic H2O2 Electroreduction

In this work, we made a ternary composite made up of polydopamine-modified carbon nanotubes and Au nanoparticles that acts as a unit to hold a redox protein. The components within the ternary complex serve as a cofactor orientation guide, a conductive element, and an electron shuttle promoter, respectively. The electrochemical reactions occurring at this electrode were dominated by the redox process of the active cofactors in hemoglobin in coordination with polydopamine, achieving favorable efficiency with charge transfer of 69.8 s −1 . The hemoglobin-based electrode displayed an efficient electrocatalytic effect toward H 2 O 2 reduction with an onset potential of 0.058 V, close to the formal potential value for heme sites on hemoglobin. The normalized turnover frequency of the substrate in hemoglobin-induced electrocatalysis was estimated to be 7.0 × 10 2  s −1 . The as-prepared hemoglobin-based electrode exhibited favorable affinity, appropriate sensitivity, and a moderate detection limit toward the substrate ( K M  = 0.214 mM, 1.01 × 10 −3 A·L·mol −1 , and 5.0 × 10 −3  mmol·L −1 ). The substrate diffusion process was identified as the key factor limiting the electrocatalytic performance of the hemoglobin-based electrode (2.23 × 10 −2  s −1 ). A glucose–H 2 O 2 biofuel cell was fabricated and could operate at an open-circuit potential of 0.72 V. Such a cell could produce a desirable power output density of ~5500 μW·cm −2 in the presence of a proton exchange membrane. Graphical Competitive ligation of heme protein with polydopamine could play a protective role against the negative effect of direct contact of the enzyme molecule with Au nanoparticles to retain the original configuration of native hemoglobin and exert its underlying electrocatalytic activity.