Direct electrochemistry and biocatalytic activity of hemoglobin entrapped into gellan gum and room temperature ionic liquid composite system

A new composite film of microbial exocellular polysaccharide-gellan gum (GG) and room temperature ionic liquid (IL) 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF₆) was firstly used as an immobilization matrix to entrap proteins and its bioelectrochemical properties were studied. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV-vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well-defined, quasi-reversible cyclic voltammetric peaks appeared in pH 7.0 phosphate buffer solutions (PBS, 0.1 M), with the formal potential (E°′) of −0.368 V (vs. SCE), which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The Hb-IL-GG-modified electrode also showed an excellent electrocatalytic behavior to the reduction of hydrogen peroxide (H₂O₂). Therefore, this kind of composite film as a novel substrate offers an efficient strategy and a new promising platform for further study on the direct electrochemistry of redox proteins and the development of the third-generation electrochemical biosensors.