Direct electron transfer and electrocatalysis of hemoglobin in ZnO coated multiwalled carbon nanotubes and Nafion composite matrix

ZnO coated multiwalled carbon nanotubes (ZnO-MWCNTs) nano-composite was synthesized by the hydrothermal method and expected to offer a promising template for biosensor fabrication due to satisfying biocompatibility and improved properties. The ZnO-MWCNTs nano-composite was mixed with Nafion solution to form a composite matrix for the fabrication of hemoglobin (Hb) biosensor. This composite matrix combined the advantages of inorganic composite (ZnO-MWCNTs) and organic polymer (Nafion) and could promote the direct electron transfer of Hb. The Hb/ZnO-MWCNTs/Nafion film exhibited a pair of well-defined, quasi-reversible redox peaks with a formal potential of − 0.353 V (vs. SCE), characteristic of heme redox couple (Fe(III)/Fe(II)) of Hb. Hb retained its near-native conformation in the composite film. The immobilized Hb showed fast and excellent electrocatalytic activity to H2O2 with a linear range from 2 × 10− 7 to 1.2 × 10− 5 M, and the detection limit was 8.4 × 10− 8 M. The sensitivity and apparent Michaelis–Menten constant were 1.31 A/(M·cm2) and 82.8 μM, respectively, which indicated that Hb had a high affinity to H2O2. This biosensor also showed excellent electrocatalytic activity towards trichloroacetic acid.