Electrochemistry and electrocatalysis of hemoglobin on multi-walled carbon nanotubes modified carbon ionic liquid electrode with hydrophilic EMIMBF4 as modifier

The direct electrochemistry of hemoglobin (Hb) on multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was achieved in this paper. By using a hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as the modifier, a new CILE was fabricated and further modified with MWCNTs to get the MWCNTs/CILE. Hb molecules were immobilized on the surface of MWCNTs/CILE with polyvinyl alcohol (PVA) film by a step-by-step method and the modified electrode was denoted as PVA/Hb/MWCNTs/CILE. UV–vis and FT-IR spectra indicated that Hb remained its native structure in the composite film. Cyclic voltammogram of PVA/Hb/MWCNTs/CILE showed a pair of well-defined and quasi-reversible redox peaks with the formal potential (E0′) of −0.370 V (vs. SCE) in 0.1 mol/L pH 7.0 phosphate buffer solution (PBS), which was the characteristic of the Hb heme FeIII/FeII redox couples. The redox peak currents increased linearly with the scan rate, indicating the direct electron transfer was a surface-controlled process. The electrochemical parameters of Hb in the film were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (ks) as 0.49 and 1.054 s−1, respectively. The immobilized Hb in the PVA/MWCNTs composite film modified CILE showed excellent electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and hydrogen peroxide. So the proposed electrode showed the potential application in the third generation reagentless biosensor.