Direct electrochemistry and electrocatalysis of hemoglobin entrapped in composite matrix based on chitosan and CaCO3 nanoparticles

The direct electron transfer between hemoglobin (Hb) and the underlying glassy carbon electrode (GCE) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and inorganic CaCO₃ nanoparticles (nano-CaCO₃). Cyclic voltammetry of Hb-CHT/nano-CaCO₃/GCE showed a pair of stable and quasi-reversible peaks for HbFe(III)/Fe(II) redox couple in pH 7.0 buffer. The electrochemical reaction of Hb immobilized in CHT/nano-CaCO₃ composite matrix exhibited a surface-controlled process accompanied by electron and proton transfer. The electron transfer rate constant was estimated to be 1.8 s⁻¹. This modified electrode showed a high thermal stability up to 60 °C. The apparent Michaelis–Menten constant was calculated to be 7.5 × 10⁻⁴ M, indicating a high catalytic activity of the immobilized Hb toward H₂O₂. The interaction between Hb and this nano-hybrid material was also investigated using FT-IR and UV–vis spectroscopy, indicating that Hb retained its native structure in this hybrid matrix.