Preparation And Electrochemical Performance Of Alginate Nanocomposite Modified Electrode

In the preparation of electrochemical biosensors,the immobilization of proteins on the electrode directly affects the performance of the sensors.In order to preferably achieve the electrochemical behavior of the biosensors,the new and biocompatible materials,and the effective fixation methods are required to maintain the biological activity of the protein and increase the protein fixing amount..In this,sodium alginate?SA?,an anionic polymer with gelation,biocompatibility and film-forming property,and the octylamine modified alginate derivative?Oct-Alg?are respectively used to prepare biosensors.Nanomaterials with the merits such as large surface area,low density,high electrochemical activity,non-toxic and good electrical conductivity,etc.,has become excellent materials for the fixation of proteins..In contrast to other methods,electrodeposition not only provides a simple and convenient technique for the construction of the protein electrode,which can make the protein strongly be adsorbed on the surface of the base electrode nearly without denaturation,but also makes the construction of the biosensor reproducible and makes the electroactive materials be uniformly dispersed in the resultant biocomposite film.This method greatly improves the stability of the biosensor and effectively promotes direct electron transfer rate between protein and the electrode.In the research,we mainly attempted to electrodeposit the mixture of alginate nanocomposites and redox proteins on the carbon ionic liquid electrode?CILE?to successfully fabricate the third generation of new-type electrochemical biosensors.The constructed biosensors could achieve good direct electrochemical behavior,simultaneously,the reduction of trichloroacetic acid?TCA?was also carried out on the modified electrode with good electrocatalytic property.The main work of this subject includes the following contents:?1?A novel alginate nanocomposites modified electrode based on the direct coating of octylamine modified sodium alginate?Oct-Alg?,graphene?GR?and myoglobin?Mb?mixed suspend on the surface of CILE was fabricated using Nafion as the film forming material to improve the stability of protein immobilized on the surface the electrode,which was abbreviated as Nafion/Oct-Alg-GR-Mb/CILE.FT-IR and UV-vis absorption spectra suggested that Mb could retain its native structure and activity in the Oct-Alg-GR composite film.The electrochemical behavior of the modified electrode was studied by cyclic voltammetry.A pair of symmetric and quasi-reversible redox peaks were obtained with the formal potential as-0.252 V?vs.SCE?,the electron transfer number?n?as 1.09,the charge transfer coefficient???as 0.398 and the electron transfer rate constant?ks?as 0.286 s^-1,indicating that Oct-Alg-GR composite film could provide the protein a good microenvironment to retain their native structure and bioactivity,promoting the direct electron transfer between Mb and the electrode.The modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid?TCA?with wide linear range from 4.8 to 186.3 mmol/L,low detection limit as 0.83 mmol/L?3??and apparent Michaelis-Menten constant(K_M^app)as 58.4 mmol/L.?2?The electrodeposition of Mb,SA and GR composites on the surface of CILE was performed to fabricate the modified electrode which was abbreviated as?Nafion/Mb-SA-GR/CILE?.And the structure and morphology of the modified electrode were characterized by FT-IR and UV-vis.FT-IR and UV-vis absorption spectra confirmed that Mb could retain its native structure after being immobilized in the SA-GR composite film.The CV curve of the modified electrode in the pH = 7.0 PBS exhibited a pair of quasi-reversible redox peaks with the formal potential as-0.29 V?vs.SCE?and the electron transfer rate constant?ks?was 0.138 s^-1,revealing that SA-GR composite film with good biocompatibility and electrical conductivity could provide the protein a good microenvironment to retain its bioactivity,improving the stability of the modified electrode and promoting the direct electron transfer between Mb and the electrode.Meanwhile,the modified electrode exhibited good electrocatalytic ability to the reduction of TCA with linear range from 15.0 to 69.0 mmol/L,low detection limit as 2.0 mmol/L?3??and apparent Michaelis-Menten constant(K_M^app)as 35.09 mmol/L.The modified electrode exhibited good stability and reproducibility.?3?Electrodeposition of the mixture of Mb,SA and TiO₂ nanoballs on the surface of CILE was performed to fabricate the alginate nanocomposites modified electrode which was abbreviated as Nafion/Mb-SA-TiO₂/CILE.FT-IR and UV-vis absorption spectra implied that Mb could retain its native structure and bioactivity after being immobilized in the alginate nanocomposites.Nafion/Mb-SA-TiO₂/CILE displayed a pair of good shape and quasi-reversible redox peaks in the CV curve,indicating that the direct electron transfer of Mb could be realized on the modified electrode.The good biocompatibility of SA,the good electrocatalytic ability of TiO₂ nanoballs,and their synergistic effects were beneficial to the electron transfer between Mb and CILE.The modified electrode exhibited good electrocatalytic ability to the reduction of TCA with wide linear range from 5.3 to 114.2 mmol/L,low detection limit as 0.152 mmol/L?3??and apparent Michaelis-Menten constant K_M^app as 32.3 mmol/L.?4?A novel electrochemical biosensor was successfully fabricated by immobilizing Mb on CILE via electrodeposition method,using biocompatible SA and Fe₃O₄-GR nanocomposites as the matrix.FT-IR and UV-vis absorption spectra simultaneously suggested that Mb could retain its native structure after being immobilized in the SA-Fe₃O₄-GR composite film.The electrochemical behavior of the modified electrode was studied by cyclic voltammetry,and a pair of symmetric redox peaks appeared in the cyclic voltammograms with the electron transfer number?n?as 0.982,the charge transfer coefficient?a?as 0.357 and the electron transfer rate constant?ks?as 0.234 s^-1,indicating that the special structure of Fe₃O₄-GR were beneficial for electron transfer between Mb and the modified electrodes.In addition,the constructed sensor possessed wide linear range,high sensitivity,good repeatability and stability.?5?A new-type electrochemical biosensor was fabricated by electro-co-deposition of sodium alginate/MnO₂-C/Mb composite on the CILE.FT-IR and UV-vis absorption spectra implied that Mb could retain its native structure and bioactivity in SA/MnO₂-C composite.Due to the good biocompatibility,large surface area of the SA/MnO₂-C composite,it could provide a very suitable microenvironment for Mb.SEM c-an obviously observe the surface morphology of MnO₂-C microspheres.A pair of symmetric redox peaks appeared in the CV curve,suggesting that the constructed biosensor exhibited good direct electrochemical behavior,and also indicating that the unique structure and large surface area of MnO₂-C microspheres could promote the electron transfer between Mb and modified electrode.The reduction of TCA was also carried out on the modified electrode with wide linear range as 5.2-128.2 mmol/L and detection limit as 0.152 mmol/L.