Study And Application Of Cu And Co Metal Sulfide Nanocomposites In Electrochemical Sensing Technology

Electrochemical immunosensors developed based on the principle of specific binding between antibody and antigen have been widely applied in many fields due to merits of high sensitivity,rapid detection,simple operation and low cost.Metal sulfide compounds with excellent physichemcal properties can combine with noble metals or graphene-based materials,which shows great potential in developing electrochemical immunosensors with versatile detection modes with significant application in the sensitive,accurate and fast analysis of biomarker samples.The detailed works in this thesis are as follows:At first,a bifunctional Pd-decorated polysulfide nanoparticle of Co₉S₈ supported on graphene oxide（G/Co₉S₈-Pd）was used to build a label-free immunosensor for amyloidβ-protein（Aβ）detection.The Co₉S₈ grafted on the conductive support of graphene,which can prevent the aggregations of Co₉S₈ and improve the conductivity of the nanocomposites of G/Co₉S₈.A large of Pd nanoparticles（NPs）loaded on G/Co₉S₈ surfaces,and thus provided more sites to attach Aβantibodies by the chemical bond of Pd-N.As expected,the novel G/Co₉S₈-Pd nano-composites showed an excellent electrocatalytic activity for H₂O₂ reduction,good conductivity and high specific surface area.The efficient catalytic activity originated from the effects of integration and synergy among the Co₉S₈,Pd NPs and GO.Additionally,the G/Co₉S₈-Pd was applied as matrix and signal indicator in our immunosensor and obtained a high sensitivity for Aβdetection.The developed immunosensor performed a wide linear range（0.10 pg/mL to 50 ng/m L）,and a low detection limit（41.4 fg/mL）.Beyond that,the immunosensor exhibited a remarkable analytical ability and wide application in the field of clinical medical examination and treatment.Based on the above work,using the good conductivity and catalytic performance of the cobalt sulfide,the Sn element was doped into cobalt sulfide by co-precipitation to synthesize an amorphous ternary metal sulfide of CoSnS_x.The amorphous nanoparticles can provide more active site.More than that,it performed excellent performance of signal marker was induced by the synergistic effect between stannic sulfide and cobalt sulfide,as well as the loaded Pd nanoparticles（NPs）.Both CoSnS_x and Pd NPs presented excellent electrocatalytic activity toward H₂O₂ oxidation.Moreover,the magnetic nanocomposite of Fe₃O₄@PPy-Au was firmly immobilized on the magnetic glassy carbon electrode（MGCE）by the magnetic force.The magnetic substrate not only performed good electron conductivity,but also improved the stability of the fabricated electrochemical immunosensor.The developed immunosensor for the NT?pro BNP detection exhibited a wide linear response（0.10 pg/mL to50 ng/mL）,and low detection limit of 31.5 fg/mL.In addition,the immunosensor held an excellent analysis capability and broad fascinating application for the detection of other biomarkers in medical diagnosis and treatment.The detection of insulin by electrochemical immunoassay is desirable but highly challenged due to the obstacle of improving accuracy,especially in single response system.In order to get an more accuracy electrochemical immunosensor for the biomarker analysis,fabricated a dual mode electrochemical immunoassay based on Cu₇S₄-Au as a dual signal indicator for insulin.Cu₇S₄ presents a strong differential pulse voltammetry（DPV）signal for the electron transfer between the Cu²⁺and Cu⁺,without the addition of K₃Fe（CN）₆ or other electron transfer mediators.Furthermore,Cu₇S₄ displays high sensitivity and high electrocatalytic activity towards the reduction of H₂O₂ through chronoamperometry.The introduction of Au nanoparticles can not only link on the surface of Cu₇S₄ by the chemical bond of Au-SH,but also connect the second antibody（Ab₂）by the chemical bond of Au-N.Due to the superior electroconductivity of Au nanoparticles and the synergistic effect between the Au nanoparticles and Cu₇S₄,a high sensitivity is achieved by means of DPV and chronoamperometry.To improve loading capacity of antibodies,nanofibers polyaniline covalently-grafted graphene（GS-PANI）linked with Au NPs（GS-PANI-Au）as the matrix material was prepared.Based on Cu₇S₄-Au as a double signal indicator,the developed electrochemical immunoassay for insulin exhibits a wide linear response for insulin detection in the range from 0.10 pg/mL to 50 ng/mL,with low detection limit of 35.8 fg/mL and 12.4fg/mL through two modes,respectively.Furthermore,the immunosensor performs an excellent analytical capability for insulin and promises the application for quantitative detection of other disease markers in clinical diagnosis.Based on the above experiment we can get the copper sulfide performed strong signal without any electron mediator,and cobalt sulfide performed good electrical conductivity and high electrocatalytic activity towards H₂O₂ redox reactions.A dual-mode electrochemical immunosensor with CuCo₂S₄-Au bimetallic sulfides as enhancer for accurate detection of PCT was fabricated.The immunosensor not only displays a heavy square wave voltammetry（SWV）signal due to the electron transfer of Cu²⁺and Cu⁺but not the addition of electron mediators.But also presents high electrocatalytic activity towards H₂O₂ redox reactions and enhances the detection sensitivity of the amperometric i-t curve（i-t）.To firmly immobilize antibodies,electrolytic gold was used as the matrix for the immunosensor.Based on a CuCo₂S₄-Au dual-signal indicator and electrolytic gold as the matrix,the developed immunosensor for PCT detection in this study demonstrates a wide linear response（0.10pg/mL to 50 ng/mL）and a low detection limit（SWV:82.6 fg/mL and i-t:95.4 fg/mL）.Additionally,the fabricated immunosensor exhibited an outstanding analytical approach for PCT and broad application for other biomarkers in clinical diagnosis and treatment.Based on Cu₇S₄-Au as a double signal indicator which achieved a sensitivity and accuracy detection of insulin.There were some reports that silver nanoparticles（Ag NPs）show strong DPV signal of Ag/Ag⁺and at different potential of Cu₇S₄.Under this circumstance,we want to combine the unique advantages of Cu²⁺/Cu⁺and Ag/Ag⁺,and get a more accuracy immunosensor for biomarkers detection.Ag⁺can react with Cu₇S₄ and the ion-exchange reaction takes place in a short time(6Ag⁺+Cu₇S₄→2Ag₃CuS₂+4Cu⁺+Cu²⁺).Ag₃CuS₂nanocages can be successfully synthesized by the ion-exchange route.During the DPV detection of Ag₃CuS₂,we get three peak currents at different potential.In previous work,the Cu₇S₄ not only displayed a strong DPV signal,but also performed high electrocatalytic activity towards the reduction of H₂O₂.After the introduction of Ag⁺,the electrocatalytic activity is also improved.As a result,the Ag₃CuS₂ combined the advantage of both sides.Based on this,a multi-signal mode label-free electrochemical immunosensor was fabricated in this work,this immunosensor shows an accurate signal,wide linear range and sensitivity for CYFRA21-1.