Direct electrochemistry and electrocatalysis of hemoglobin entrapped in semi-interpenetrating polymer network hydrogel based on polyacrylamide and chitosan

Semi-interpenetrating polymer network (semi-IPN) hydrogel based on polyacrylamide (PAM) and chitosan was prepared to immobilize redox protein hemoglobin (Hb). The Hb–PAM–chitosan hydrogel film obtained has been investigated by scanning electron microscopy (SEM) and UV–VIS spectroscopy. UV–VIS spectroscopy showed that Hb kept its secondary structure similar to its native state in the Hb–PAM–chitosan hydrogel film. Cyclic voltammogram of Hb–PAM–chitosan film-modified glass carbon (GC) electrode showed a pair of well-defined and quasi-reversible redox peaks for Hb Fe(III)/Fe(II), indicating that direct electron transfer between Hb and GC electrode occurred. The electron-transfer rate constant was about 5.51 s− 1 in pH 7.0 buffers, and the formal potential (E°′) was − 0.324 V (vs. SCE). The dependence of E°′ on solution pH indicated that one-proton transfer was coupled to each electron transfer in the direct electron-transfer reaction. Additionally, Hb in the semi-IPN hydrogel film retained its bioactivity and showed excellent electrocatalytic activity toward H2O2. The electrocatalytic current values were linear with increasing concentration of H2O2 in a wide range of 5–420 μM. The unique semi-IPN hydrogel would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.