Research And Application Of Electrochemical Immunosensor Based On Two-dimensional Nanomaterial

Cancer has already been one of the most serious threats of human health.At the current level of science and technology,early diagnosis is the key to effective treat cancer.Tumor markers are important medium and widely used in early diagnosis.Biosensors play more and more crucial role in modern laboratory and clinical analysis of chemical and biological material.Particularly,biosensors based on two-dimensional(2D)layered nanomaterial have attracted the research interests of many people due to the unique electronic,optical,and chemical characteristics.In this paper,we designed biosensor based on 2D nanomaterial and their composites to detect tumor markers.The main reseach systems are as follows:1.Stable and uniform Au@Ag nanoparticles(NPs)were prepared,which have the stability of Au NPs and catalytic performance of Ag NP.A novel sandwich-type electrochemical immunosensor was constructed based on Au@Ag NPs together with horseradish peroxidase(HRP)were used as labels of secondary antibody.Au@Ag NPs could effectively improve the catalytic activity of HRP,and could be regarded as peroxidase-like to amplify electrochemical reaction signal of hydroquinone and hydrogen peroxide.Due to the excellent conductivity and large surface area,chitosan functionalized nitrogen-doped graphene sheets(CS-NG)were used as a platform to firmly immobilize primary antibody(Ab1).Under the optimum conditions,the linear range of carcinoembryonic antigen(CEA)concentration was 0.0001~100 ng mL-1,and the limit of detection(LOD)could be as low as 0.05 pg mL-1.Meanwhile,the immunosensor also showed acceptable selectivity,reproducibility and stability.2.In this work,graphite-like carbon nitride nanosheets coupled with layered MoS2 were synthesized via a directly mixing and calcination method,and served as highly efficient luminescent material in an electrochemiluminescent(ECL)immunosensor.The prepared g-C3N4/MoS2 nanosheets exhibited strong and stable cathodic ECL activity compared to individual g-C3N4.A reason is that the combination between the g-C3N4 and MoS2 would promote charge transfer and,thus,enhance the separation efficiency of electron-hole pairs,reduceing the passivation of g-C3N4.The ECL assay for alpha-fetoprotein(AFP)detection based on g-C3N4/MoS2 nanosheets was developed with excellent sensitivity of a concentration variation from 0.001 to 50 ng m L-1 and limit of detection(LOD)down to 0.33 pg m L-1.Therefore,it is of great significance for developing immunosensors to detect tumor diagnostics based on MoS2/g-C3N4 sheet nanocomposites.3.A novel label-free electrochemiluminescent(ECL)immunosensor based on CdS-MoS2 and dual coreactants was designed for detection of procalcitonin(PCT).The sheet CdS-MoS2 composites were synthesized through a simple one-pot hydrothermal method,and served as highly efficient luminescent material in an ECL immunosensor.Due to the large specific surface area,and decreased band gap,CdS-MoS2 nanocomposites manifested a superior electrocatalytic reduction of S2O82-,which produced large amounts of hole-donors(SO4·-).In addition,the introducing of H2O2 could induce decomposition of S2O82-into SO4·-.The synergistic effects of CdS-MoS2 nanocomposites and dual coreactants enhanced the ECL signal and improved the sensitivity of the immunosensor.Under optimum conditions,the ECL assay for PCT detection was developed with excellent sensitivity of a concentration variation from 0.0001 to 10 ng m L-1 and limit of detection down to 33 fg m L-1.Meanwhile,the immunosensor also showed acceptable selectivity,reproducibility and stability.4.The label-free electrochemical immunosensor was developed based on MoS2/Au.With MoS2/Au as the sensor platform,H2O2 as the probe,using the change of current before and after the immunological recognition of antigen-antibody detected alpha-fetoprotein(AFP).The good electroconductibility,biocompatibility of AuNPs and excellent catalytic properties of MoS2 toward H2O2,improved the sensitivity of the immunosensor.Under optimum conditions,the electrochemical immunosensor for PCT detection was developed with excellent sensitivity.The concentration variation was from 0.005 to 50 ng mL-1 and limit of detection evaluated to be down to 2.5 pg mL-1.5.The electroconductibility of MoS2 was enhanced by electrochemical reduction.And after electrochemical deposition Au nanoflower on rMoS2,the electroconductibility and biocompatibility of modified electrode(Au NFs/rMoS2/GCE)were enhanced further.Experimental results showed that AuNFs/rMoS2/GCE could promote charge transfer in solution of [Fe(CN)6]3-or ferrocene(Fc).We prepared DNA biosensor based on rMoS2/AuNFs and Exo III-assisted target recycling amplification strategies.The hairpin DNA labeled ferrocene(Fc)in the middle as capture probe,was first selfassembled on the AuNFs/rMoS2/GCE surface by Au-S bond.In the presence of the target DNA(T-DNA),the T-DNA hybridized with HP and a probe-target duplex with a blunt end at the 3?-termini of HP is formed,which triggered the Exo III cleavage process accompanied by the releasing of T-DNA.As a result,the Fc tags were close to the electrode surface because the remaining single-stranded HP with tailor-made complementary bases at both ends could form a hairpin structure.The change led to the increase of the oxidation peak current of Fc.T-DNA was detected sensitively based on the signal change of Fc.