3D Flexible Electrode Based On Carbon Nanocomposites:Preparation And Application For Electrochemical Sensor

With the prolongation of the average life span of human beings,cancer has become increasingly prominent threat and one of the major global health problems.Cancer has some special biological characteristics such as abnormal cell differentiation and proliferation,loss of growth control,which make hydrogen peroxide levels in cancer cells are much higher than the corresponding normal tissue cells.The electrochemical methods have been widely applied in the detection and analysis of small biological molecules due to quick response,high sensitivity,simple instrument,easy to operate and realize further automatic continuous measurement and control.Therefore,constructing an appropriate electrochemical detection platform for quickly and accurately detection of intracellular reactive oxygen species is beneficial to the early diagnosis and treatment of cancer.Carbon nanomaterials have been widely applied in the field of electrocatalytic analysis due to their good electrical conductivity and high specific surface area.The design of flexible electrode substrates has attracted tremendous research efforts.Several flexible one-dimension（1D）,two-dimension（2D）and three-dimension（3D）carbon materials,such as 1D carbon fiber（CF）,2D graphene paper and 3D graphene foam,have been developed in constructing electrochemical biosensors for their special features including high chemical stability,good biocompatibility,and intrinsic flexibility and mechanical strength..Based on the above developments and requirements,four novel carbon-based functional nanocomposites were been prepared and applied in electrochemical biosensors in this paper.We also have established an electroanalytical technology platform for real-time monitoring the released amount of H₂O₂ in cancer cells under normal/stress conditions and after receiving radiotherapy or chemotherapy,providing an important massage for the changes of chemical information in vivo.The main research content has listed as the following:1.In order to achieve the self-assembly of graphene gel at low temperature,the gel can be made as a freestanding paper electrode and its catalytic sensing for hydrogen peroxide,we present the preparation of a new type of 3D porous imidazolium-based ionic liquid（IL）-functionalized graphene framework（GF）by a facile and efficient one-pot self-assembly at low temperature with the assistance of reducing agent dopamine（DA）,exhibiting a typical hierarchical pore structure.Simultaneously,the chloroauric acid precursors were chemically reduced in situ on the IL-GF scaffold,forming highly dense and well dispersed gold nanoflowers,which are dense and uniformly dispersed on the IL-GF scaffold.The composite material was processed into a self-supported paper electrode.Due to the unique three-dimensional porous structure of the material and the synergistic effect between different components,the resultant AuNFs/IL-GF composites have excellent electrocatalytic activity for H₂O₂ detection.Furthermore,the obtain paper electrode can be used to detect the level of H₂O₂ secreted by different cells,which can used for separating different cells,and further evaluated the effect of radiotherapy and chemotherapy of different cancer cells.2.In order to further improve the space-time resolution of the electroanalytical method and the detection sensitivity of the actual sample,a novel microelectrode is designed at this work.A noble Au/MnO₂/ERGO nanocomposites with hierarchical structure on carbon fiber substrate was designed and fabricated by a simple and effective in-situ electrochemical method.Graphene oxide（GO）nanosheets were first coated on bare CF by dip coating.Then the GO was further reduced to graphene under electrochemical production process,which can dramatically increase the electrical conductivity,surface area,and hydrophilicity of CF.Secondly,the surface of graphene wrapped CF has further been covered by twisted and intersectant MnO₂ nanowires through template-free electrodeposition,which provide a large surface area and abundant nucleation sites for the further electrodeposition of electrocatalytically active Au nanoparticles onto it.Utilizing the hierarchical structural characteristics of the microelectrode and the well-dispersed Au nanoparticles,the synthesized nanostructured microelectrode exhibits a high catalytic efficiency for hydrogen peroxide and can be used for the efficient and ultrasensitive electrochemical detection of of H₂O₂ released from HeLa cells and HBL-100 cells.3.Based on the poor conductivity and disordered growth of the MnO₂ nanowire layer in the hierarchical structure microelectrode in Chapter II,resulting in a large electrode impedance,which is not conductive to make full use of Au nanoparticles.And constructing ordered three-dimensional nanoarrays is an effective way to increase the active area of the electrode.Herein,highly ordered nitrogen doped carbon nanotube arrays were wrapped on carbon fiber by using ZnO nanoarrays as templates,polydopamine as a carbon source and nitrogen source,then gold nanoparticles were decorated on the arrays surface by using the reducibility of polydopamine,therefore a new type of flexible nanohybrid microelectrode was synthesized.This method can lower the electrode impedance,increase the specific surface area and load sites,reduce the size of gold nanoparticles to 5 nm.Due to synergistic effect between the nitrogen-doped carbon tube and the loaded gold nanoparticles,the microelectrode not only demonstrates a high electrocatalytic activity towards H₂O₂ reduction,but also high sensitivity,wide liner response range from 0.5μM to 4.3μM.And the fiber electrode can also be placed near the cell to increase accuracy of the current response of different cells under stress conditions.By comparing and calculating the number of H₂O₂ molecules released under different stress states,an electrochemical method for indirect identification of different types of cells was established.4.Based on the three-dimensional nanoarrays,a coral micro-nanostructure arrays of hollow carbon nanotube@carbon nanospheres is further designed on carbon fiber substrate to increase the specific surface area and noble metal loading site of the electrode so that the electrode is in full contact with the tested solution,thereby improving the electrode detection sensitivity.The novel microelectrode is synthesized by hydrothermal self-assembly,which glucose and zinc oxide nanoarrays were used as precursors and sacrificial templates,respectively.The special hierarchical structure dramatically increases the specific surface area of carbon fiber and provides more active sites for supporting the precious metal nanoparticles,which is beneficial to the catalyst in full contact with the test solution.The formation mechanism of this special nanotube-nanosphere structure is discussed by changing the precursor concentration.Using this nanocomposite as a carrier,the surface of the carbon material is electrically activated in H₂SO₄ solution with Pt networks used as counter electrodes,which improved the utilization and catalytic activity of the precious metal.Transmission electron microscopy（TEM）and X-ray diffraction（XRD）showed multiple crystal faces of the Pt nanoparticles in the composite material,indicating that the size of Pt nanoparticles is 2 nm and has uniform distribution.Using this nanocomposite microelectrode,the important electrochemical methods such as linear sweep voltammetry and chronoamperometry were used to study the electrochemical catalytic effect of hydrogen peroxide reduction.The results show that the nanocatalyst has good catalytic activity,good flexibility,low detection limit（50 nM）,wide linear range（range from 0.1μM to 10.69μM）,and can be used to detect the release of hydrogen peroxide from different types of breast cells.