Research Of Electrochemical Immunosensors For Tumor-marker Assays Based On Polydopamine As Label Materials

Biosensor is a kind of analysis device,which combines certain biomaterials,biologically derived materials or biomimetic materials to a physical or chemical converter,to generate continuous electivity in response to the concentration of a certain analytes or a group of analytes.In China,the number of new cancers and deaths has been increasing year by year,and the mortality caused by malignant tumors has risen to the top.Early diagnosis and treatment of cancer can greatly improve the cure rate of cancer.Therefore,the study of ultrasensitive electrochemical immunosensor to detect tumor markers is of great significance for early diagnosis and treatment of tumors.Polydopamine?PDA?with advantages such as simple synthesis,rich functional groups,and good biocompatibility is mostly used as structural materials or molecularly imprinted polymers?MIP?in the fabrication of sensors.However,its electrochemical properties have been rarely studied,not to mention being utilized as electrochemical markers in electrochemical biosensors.Therefore,this topic is devoted to exploring the electrochemical properties of polydopamine and using polydopamine as a core material to construct electrochemical immunosensors to achieve ultrasensitive detection of tumor markers.Combining the electrochemical property of polydopamine with its other properties,two kinds of polydopamine nanoparticles?PDANPs?with excellent electrochemical property were designed.The innovative results of this dissertation are summarized as follows:?1?Polydopamine nanoparticles with narrow size was prepared through a one-step reaction based on the fact that dopamine will spontaneously polymerize in alkaline.PDANPs do not have electrochemical signal themselves.However,though exchanging electrons with Fc,signal can be generated indirectly in the form of increasing the oxidation current of charge transfer of Fc.For the first time,it has been found that polydopamine has the property of amplifying electrochemical signals and the potential to be utilized as electrochemical marker to construct biosensor.?2?A sandwich-type electrochemical immunosensor was constructed to sensitively detect the tumor marker,alpha-fetoprotein?AFP?with PDANPs as electrochemical marker and nano-gold electrode as platform.The electrochemical performance of the AFP immunosensor was studied in PBS containing mediator Fc with CV.Under optimal conditions,the constructed AFP immunosensor exhibited a wide linear range from 1 pg m L^-1 to 50 ng m L^-1 with a low detection limit of 0.3 pg m L^-1.as well as excellent stability,reproducibility and selectivity.Measurements of AFP in human serum gave excellent correlation with clinical standard Assay.?3?Using Fe₃O₄ nanoparticles as core and lysozyme?Lyz?as template molecule,Fe₃O₄@PDA molecular imprinted polymers?MIP?with selective adsorption of lysozyme was prepared.Electrochemical tests revealed that Fe₃O₄@PDA MIP also has an amplification effect on the mediator Fc.Combining those two properties,it's hopeful to obtain“antibody mimics”with electrochemical signal.Compared with nature antibody,“antibody mimics”is cheaper,more stable and can be recycled,which can be utilized in the fabrication of electrochemical immunosensor to improve the stability and lower the test cost.