Construction Of Sensing Interface On Graphene Fiber Electrode And Its Application In The Electroanalysis Of Small Biomolecules

Bioactive small molecules,such as reactive oxygen,dopamine,etc.,are important substances in life activities and closely related to human health.Therefore,it is necessary to establish a rapid and sensitive detection system of bioactive small molecules in physiological samples,which is of great significance for the prevention,diagnosis and treatment of diseases.Electrochemical sensors are used in life sciences and clinical medicine due to their simple operation,high sensitivity,rapid response,and ease of online access.As a frontier field of electroanalytical chemistry,microelectrodes provide a new horizon for detecting intracellular biomolecules and studying the laws of cell and human life activities owing to their small size,fast mass transfer rate,high signal-to-noise ratio,and short response time.Compared with traditional carbon fiber and metal fiber electrodes,graphene fiber（GF）has the advantages of good mechanical properties,adjustable structural size,and easy functionalization,and can be used as microelectrode for electrochemical sensing.Therefore,taking GF as the research object,a series of functional nanomaterials sensitized microelectrode sensing interface was established by constructing hierarchical porous nanoarray structure on its surface and doping with heterogeneous elements,and applied in the electrochemical detection of bioactive small molecules in body fluids,cells and tissue systems.The main research contents are as follows:（1）To improve the electrocatalytic activity of GF,Au nanoparticles（Au-NPs）wrapped flower-like Mn O₂ nanowires（Mn O₂-NWs）assembly modified GF（Mn O₂-NWs@Au-NPs/GF）was prepared by two-step electrodeposition method and applied in electrochemical detection of hydrogen peroxide（H₂O₂）released from cancer cells.Benefiting from the advantage of the unique hierarchical nanohybrid structure and the high electrocatalytic activity of Au-NPs and Mn O₂-NWs,the resultant Mn O₂-NWs@Au-NPs/GF microelectrode shows good catalytic activity towards the electrochemical redox reaction of H₂O₂.When used in amperometric detection of H₂O₂,the nanohybrid microelectrode exhibits high sensitivity(32.9μA cm^-2 m M^-1)and low detection limit（1.9μM）as well as good anti-interference ability,reproducibility and stability,and can be used in real-time in situ detection of H₂O₂released from human breast cancer cells,which provides an effective strategy to distinguish cancer cells from the normal one and identify different types of cancer cells.（2）To further enhance the biocompatibility and electrocatalytic activity of GF,three types of binary co-doped graphene fiber（GF）were synthesized using graphene oxide nanosheets as the building block and eco-friendly ionic liquid（IL）molecules as the heteroatoms-containing precursor by wet co-spinning and high-temperature pyrolysis,where the type of heteroatoms doped in graphene can be adjusted by choosing different IL molecules.Among different multi-heteroatoms co-doped GF microelectrodes,N,B co-doped GF（NBGF）possesses the largest electrochemical active surface area and lowest charge transfer resistance,and shows the highest electrocatalytic activity towards H₂O₂reduction.When used in amperometric detection of H₂O₂,NBGF microelectrode exhibits excellent sensing performance with a high sensitivity of 431.37μA cm^-2m M^-1,a low detection limit of 350 n M,as well as good mechanical flexibility and biocompatibility,these enable it to be used for real-time tracking H₂O₂ released from different colorectal cancer cells,which provide the possibility to distinguish different types of cancer cells and evaluate the efficacy of chemotherapy drugs by calculating the average number of H₂O₂ secreted per cell.Moreover,the proposed NBGF microelectrode has been applied in in situ sensitive detection of H₂O₂ in tumor tissue from female Balb/c mice.（3）Given the unique mechanical flexibility of the fiber electrode,GF can also be integrated into a microfluidic chip.Based on this,a 3D honeycomb-like porous nickel-cobalt phosphide nanosheet arrays（Ni Co P-NSAs）modified GF microelectrode（Ni Co P-NSAs/GF）was prepared by using solvent thermal reaction and low-temperature phosphating treatment.By the integration of the Ni Co P-NSAs/GF microelectrode into microfluidic chip,a new type of electrochemical microfluidic sensor chip was constructed for the sensitive detection of DA in body fluids.Honeycomb Ni Co P-NSAs have a 3D porous structure,which improves the electrochemical activity area of the microelectrode,facilitates the exposure of active sites,and significantly enhances the electrocatalytic activity of Ni Co P-NSAs/GF microelectrode towards dopamine（DA）.When used to detect DA,Ni Co P-NSAs/GF microelectrode exhibits excellent sensing properties with a sensitivity of5.56μA cm^-2μM^-1,a low detection limit of 13.9 n M,as well as good selectivity,reproducibility and stability,and can be used for in-situ detecting DA released by human neuroblastoma cells.In addition,the electrochemical microfluidic sensor chip constructed by Ni Co P-NSAs/GF microelectrode enables sensitive detection of DA in trace urine and serum samples.（4）As DA,ascorbic acid（AA）and uric acid（UA）coexist universally in organisms,the cobalt and nitrogen co-doped GF（Co NGF）was prepared by wet co-spinning and high-temperature pyrolysis the mixture of phthalocyanine cobalt（II）and GO to simultaneous detect AA,DA and UA.Co and N co-doping produced abundant defects and a large number of Co-N active sites and improved the conductivity and electrocatalytic activity of GF,which can be used for the simultaneous detection of AA,DA and UA.The sensitivities are0.06,1.77 and 1.06μA cm^-2μM^-1,and the detection limits are 1.65,0.05 and 0.17μM for AA,DA and UA,respectively.Further,the electrochemical microfluidic sensor chip based on the Co NGF microelectrode also realized the simultaneous detection of AA,DA and UA in trace urine samples.