The Application Of Rare Earth Oxide In The Direct Electrochemistry Of Redox Proteins

Protein and enzyme are among the most widely-used biofunctional reagents for immobilization in the field of electrochemical biosensor. They are involved in metabolism and other important physiological processes all of which contain electron transfer. The adoption of electrochemistry method will be helpful for the investigation of the electron-transfer processes of protein and enzyme. Moreover, the investigation of the direct electrochemistry of protein can help us comprehend the dynamic and thermodynamic properties of protein, establish a solid foundation to explore the biological oxidation and reduction processes, and is vitally significant for the theoretical and applicational research of new-generation biosensors, biological fuel batteries and so on.The present research takes the rare earth oxide materials (ceria and thulium) as the biological carrier of hemoglobin (Hb) and glucose oxidase (GOD) which are the biological molecules to be used to prepare a series of enzyme electrodes. It mainly discusses the application of rare earth oxides in the direct electron transfer and biological catalytic of Hb and GOD by electrochemical methods.The results show that: rare earth oxide materials can promote the electron transfer of Hb and GOD and achieve their bio-electrocatalysis.Firstly, CeO₂ shows an excellent biocompatibility and provides a friendly microenvironment for the electron transfer between Hb (or GOD) and electrode. Hb immobilized on Nafion-CeO₂ film retains its native secondary structure, achieves direct electron transfer with the apparent heterogeneous electron transfer rate constant (ks) of (0.68±0.09) s^-1 and shows an excellent bioelectrocatalytic activity to the reduction of hydrogen peroxide. The electrocatalytic response of the biosensor varies linearly with the H2O2 concentration ranging from 2.45 to 19.6μmol·L^-1 with a detection limit of 1.013μmol·L^-1 and good long-term stability; GOD immobilized on Nafion-CeO₂ film achieves its direct electron transfer with the apparent heterogeneous electron transfer rate constant (ks) of (3.89±0.19s^-1) s^-1 and maintains its bioelectrocatalytic activity to the oxidation of glucose. The electrocatalytic response shows a linear dependence on the glucose concentration ranging from 0.5 to 4.5 mmol·L^-1. It also exhibits high stability and very good reproducibility for the detection of glucose. Secondly, Tm₂O₃ nanoparticles synthesized by the hydrothermal homogeneous method indicate an excellent biocompatibility and provids a friendly microenvironment for the electron transfer between Hb (or GOD) and electrode. Hb immobilized on Nafion-Tm₂O₃ film achieves its direct electron transfer with the apparent heterogeneous electron transfer rate constant (ks) of 0.98 s^-1 and keeps its native secondary structure similar to its native state. The electrocatalytic response shows a linear dependence on the H₂O₂ concentration ranging from 2.45 to 24.5μmol·L^-1 with a detection limit of 1.813μmol·L^-1. It also has exhibited high stability and very good reproducibility for the detection of H2O2; GOD immobilized on the Nafion-Tm₂O₃ film achieves direct electron transfer with an apparent heterogeneous electron transfer rate constant (ks) of (3.27±0.43) s^-1 and keeps its bioactivity. Confirmation of the retained bioactivity can be demonstrated by its bioelectrocatalytic activity to the reduction of dissolved oxygen. The GOD/Tm₂O₃/Nafion/GC electrode displays a potential application for the fabrication of glucose biosensors with a linear glucose response up to 7 mmol·L^-1. In addition, the biosensor based on the Tm₂O₃ nanoparticle modified electrode exhibits good stability and selectivity for the detection of glucose.