Study On The Construction Of Electrochemical Immunosensor Based On Silver Nanoparticles

Acurate and rapid detection of tumor markers in human serum is particularly important for the early detection and treatment of cancer.We combined the silver nanocomposite that have good biocompatibility,good catalytic properties and excellent electrochemical properties combined with electrochemical analysis techniques to construct four different immunosensors to achieve different cancer markers sensitive detection.In this paper,silver nanoparticles were combined with other nanomaterials,and four immunosensors were prepared by the principle of signal amplification:1.An electrochemical immunosensor based on multi-walled carbon nanotubes-ferroferric oxide/silver?MWCNT-Fe₃O₄/Ag?nanocomposites was prepared for quantitative detection of carcinoembryonic antigen?CEA?.Fe₃O₄ was grafted onto MWCNTs by electrostatic adsorption,and then silver nitrate was reduced on MWCNT-Fe₃O₄ by sodium borohydride.MWCNTs-Fe3O4 had a very high surface area to volume ratio,which could load a large number of biological molecules,thus improving the sensitivity of biosensors.Silver nanoparticles modified on the electrodes produced sensitive electrochemical redox peaks.When different amounts of protein?antigen,antibody,bovine serum protein,etc.?were adsorbed on the surface of nano-silver,the surface of nano-silver was covered.The electrochemical redox peak of silver particles decreased due to the change of the effective area of bare silver particles which could react with electrodes.MWCNT-Fe₃O₄/Ag nanocomposites established an excellent biosensing platform for detecting carcinoembryonic antigens.Under the optimum conditions,CEA concentration ranged from 1 pg mL^-1 to 80 ng mL^-1,and a lower detection limit of 0.2 pg mL^-1?S/N=3?was obtained.By using CEA and ELISA to detect CEA,the difference between the two results was very small,which provided a good method for constructing high sensitivity label-free electrochemical immunosensor.2.A novel signal-amplified immunosensor was designed by using a microwave-assisted self-assembly method to synthesize Ag-ZnFe₂O₄@rGO nanocomposites.Due to the fact that graphene oxide?GO?was fully restored to rGO,and rGO stacking was effectively inhibited by insertion of small ZnFe₂O₄ NPs between the graphene sheets,the electrical conductivity of ZnFe2O4@rGO nanocomposites was significantly improved.Moreover,the conducting path between rGO and ZnFe2O4 NPs formed because the structural defects in rGO were effectively repaired by decoration with ZnFe2O4 NPs.The amplification of the signal was achieved by combining Ag NPs as an active substances with ZnFe₂O₄@rGO nanocomposites.The layer assembly process of the immunosensor was verified by cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?.Under optimal conditions,the linear relationship between current signal and AFP concentration is obtained from 1 pg mL^-1 to 200ng mL^-1.The detection limit of AFP is 0.98 pg mL^-1?S/N=3?.The prepared immunosensor has excellent specificity,good stability and reproducibility.In addition,this label-free immunosensor exhibits excellent detection performance in human serum and has broad application prospects in clinical and medical research of AFP.3.An electrochemical immunosensor based on three-dimensional structure of rGO-MWCNTs/Ag-Au nanocomposite was used to detect carcinoembryonic antigen.The3D-rGO-MWCNTs nanocomposites feature network structure which have a large specific surface area and excellent conductivity that can providing more active sites for Ag-Au bimetallic nanoparticles.At the same time,the synergistic effect of 3D-rGO-MWCNTs and Ag-AuNPs significantly improved the overall electrochemical performance of the material.Because of the excellent biocompatibility of Ag-AuNPs,the antibody can be well attached to the electrode,so the immunosensor has been successfully prepared.Under optimal conditions,the constructed immunosensor had a broad linear range(1 pg mL^-180 ng mL^-1)and a low detection limit(3 pg mL^-1)?S/N=3?.The proposed immunosensor has excellent analytical performance including good stability,reproducibility and selectivity,and also was successfully applied to the detection of CEA in human serum,which verifies its practicability.4.In the preparation of silver?Ag?nanoparticles,because of the good reducibility of polydopamine?PDA?,the reduction of AgNO₃ to AgNPs can replace the reducing agent harmful to organisms,reducing the introduction of impurities.In addition,due to the combination of Au nanoparticles with mercaptan groups on the surface of antibodies and Ag nanoparticles with amino groups on the surface of antibodies,antibodies are firmly fixed on the surface of electrodes,which enhances the sensitivity of the immunosensor.Under optimal conditions,the constructed immunosensor has a broad linear range(1 pg mL^-180 ng mL^-1)and a low detection limit(0.286 pg mL^-1)?S/N=3?.The constructed immunosensor has not only simple preparation method,mild material,good detection performance,but also has good reference value for harmless research on active proteins such as CEA.