An Electrochemical Hydrogen Peroxide Biosensor Based on Polydopamine-Entrapped G-Quadruplex-Hemin DNAzyme

The complex of G-quadruplex-hemin, named peroxidase-mimicking DNAzyme, shows a catalytic activity towards the electro-reduction of hydrogen peroxide. Although DNAzyme is popular for the preparation of colorimetric biosensors for hydrogen peroxide, it is rarely used as a catalyst in the assembly of electrochemical biosensors. Meanwhile, it is of significance to develop novel methods in immobilizing DNA for the purpose of fabrication of DNA-based biosensors. In this study, an electrochemical hydrogen peroxide biosensor was successfully constructed using polydopamine-entrapped G-quadruplex-hemin DNAzyme. G-quadruplex-hemin complex was achieved by mixing DNA and hemin. After the physical adsorption of DNAzyme on a glassy carbon electrode, a droplet of 10 μL containing 5 g L−1 dopamine in PBS (pH 8.0) was then cast onto the surface. Dopamine was oxidized by oxygen in air to form polydopamine, realizing the immobilization of DNAzyme. The influence of DNA sequence on the performance of the biosensor is investigated and different conformation-dependent response from electrochemical to optical sensors was observed. The proposed biosensor shows a linear range with the concentration from 10 μM to 1.5 mM and a detection limit of 2.2 μM for hydrogen peroxide. The results demonstrated the possibility of enzyme immobilization on an electrode through polydopamine and the substitution of G-quadruplex-hemin DNAzyme for natural enzyme.