Polyvinyl alcohol–ionic liquid composition for promoting the direct electron transfer and electrocatalysis of hemoglobin

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in polyvinyl alcohol (PVA)–room temperature ionic liquid (i.e., 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM]PF₆) composition has been investigated by using cyclic voltammetry and chronocoulometry. It is found that the composition can promote the direct electron transfer of Hb and the heterogeneous electron transfer rate constant (k_s) of immobilized Hb is enhanced to 19.9 s⁻¹. The immobilized Hb also shows high electro-catalytic activity towards the redox of oxygen, hydrogen peroxide and nitrite. The Michaelis constants (K_m) decrease to 1.2 × 10⁻⁴ M (for hydrogen peroxide) and 9.4 × 10⁻³ M (for nitrite). The surface concentration of electroactive Hb is estimated and it is ca. 1.4 × 10⁻¹⁰ mol cm⁻², meaning that several layers of immobilized Hb take part in the electrochemical reaction. When gold nanoparticles (GNP) is introduced into the composition, the resulting PVA–GNP–[OMIM]PF₆ composition presents better performance. The electrochemical characteristic of immobilized Hb is improved further. Thus PVA–GNP–[OMIM]PF₆ composition is more suitable for the immobilization of Hb. Therefore, it is a good strategy to prepare novel composition for protein immobilization by using several materials with different function.