Studies On Electrochemical Immunosensor Based On Conducting Polymers And Carbon Nanocomposites

It is important and valuable to develop highly sensitive assay for the detection of proteins in the immune-analytical field.Electrochemical immunosensors,combining immunoassay and electrochemical sensor technology,hold great promise because of short response time,high sensitivity and specificity,low cost and simple manpower requirements.An immunosensor is an analytical device that responds to a suitable combination of a biological recognition system and an electrochemical transducer.Thus the platforms eonstruction of the antibody or antigen biomolecules immobilization have been the vital step in successful development of an immunosensor.All kinds of nano-materieals have been widely used in the field of biosensor due to their unique structure and excellent physical and chemical properties.Applying nanomaterials to construct the immunoreaction interface,the performance of the biosensor including sensitivity,stability and selectivity would be greatly enhanced.In this research,graphene oxide,carbon nanotubes,graphene,AuNPs,conducting polymers and their composites were used to construct electrochemical immunosensors for sensitive and selective detection of fetoprotein and carcinoembryonic antigen.Specific content is as follows:?1?A simple label-free electrochemical immunosensor for the highly sensitive and effective detection of alpha fetoprotein?AFP?using gold nanoparticles/graphene oxide-multi-walled carbon nanotubes?AuNPs/GO/MWCNTs?composite as a signal amplification matrix has been demonstrated.The nanocomposite was synthesized in a one-pot redox reaction between GO and HAuCl₄ without using an additional reductant.Cyclic voltammetry and electroehemical impedance spectroscopy?EIS?confirmed consecutive growth of the multilayer film.Under the optimized condition,a wide analytical range(0.01-100 ng mL^-1)is covered.The correlation coefficient is0.9929,and the limit of detection is as low as 3 pg mL^-1 at a signal-to-noise ratio of 3.?2?A high performance label-free electrochemical immunosensor was fabricated for sensitive detection of alpha fetoprotein?AFP?using Au nanoparticles decorated poly?3,4-ethylenedioxythiophene?/multiwalled carbon nanotubes?AuNPs/PEDOT/MWCNTs?as a signal amplifier.Core-shell structural nanomaterials of PEDOT/MWCNTs were prepared via a liquid-liquid interfacial polymerization.Subsequently,Au NPs were confined on the composites of PEDOT/MWCNTs by chemical reduction method,which possess a high accessible surface area and a biocompatible microenvironment for the immobilization of antibodies.The developed immunosensor exhibited excellent analytical performance for the determination of AFP with linear range of(0.0005 to 10 ng m L^-1),high sensitivity,reproducibility and stability.?3?In this work,poly?3,4-ethylenedioxythiophene??PEDOT?nanorods grown on graphene oxide nanosheets?PEDOT/GO?were firstly synthesized by liquid-liquid interfacial polymerization,followed by the chemical reduction of HAuCl₄ by NaBH₄.During the reduction process,GO doped in the PEDOT was also reduced to a more conductive form of GR.The obtained AuNPs/PEDOT/GR showed excellent conductivity and large surface area.Thus,a simple and sensitive label-free immunosensor based on AuNPs/PEDOT/GR nanocomposite has been proposed to detect carcinoembryonic antigen?CEA?by measuring the change of electrochemical response before and after the immunoreaction.Under the optimized conditions,the linear range of the proposed immunosensor is estimated to be from 0.0004 to 40 ng mL^-1?R²=0.9969?and the detection limit is estimated to be 0.1 pg mL^-1 at a signal-to-noise ratio of 3,respectively.?4?In this paper,a novel,label-free and inherent electroactive redox immunosensor for carcinoembryonic antigen?CEA?based on Au nanoparticles?AuNPs?and Nile blue A?NB?hybridized electrochemically reduced graphene oxide?NB/ERGO?has been proposed.The composite of NB-graphene oxide?NB-GO?was prepared by?-?stacking interaction.Then,chronoamperometry was adopted to simultaneously reduce HAuCl₄ and nanocomposites of NB-GO for synthesizing AuNPs/NB/ERGO.Furthermore,the negative-charged AuNPs can be used to immobilize biomolecules.The immunosensor determination was based on the fact that due to the formation of antigen-antibody immunocomplex,the decreased response currents of NB were directly proportional to the concentrations of CEA.Under optimized conditions,the linear range of the proposed immunosensor was estimated to be from 0.001 ng mL^-1 to 40 ng mL^-1 and the detection limit was estimated to be 0.00045 ng mL^-1.