The Fabrication And Application Of Electrochemical Sensors Based On Novel Conducting Polymer Nanocomposites

Conducting polymers have become a research hot topic due to their unique electrical conductivity and redox properties.Conducting polymer nanocomposites not only retain the characteristics of the components,but also endow new functions of the composites.In this thesis,PEDOT,polypyrrole and polyaniline were used as basic materials,and their nanocomposites were synthesized by electrochemical methods.A series of novel conducting polymer nanocomposites were prepared by the combination of graphene oxide,carbon nanotubes,metal nanoparticles,and antifouling materials with conducting polymers.Different electrochemical sensors were fabricated for nitrite,glucose,BRCA1 and MicroRNAs detection based on conducting polymer nanocoposites.The main contents of this thesis are summarized as follow:(1)A highly stable and sensitive nonenzymatic glucose sensor was successfully constructed through a facile electrodeposition method.Graphene oxide(GO)doped poly(3,4-ethylenedioxythiophene)(PEDOT)was firstly electrodeposited onto a glass carbon electrode using cyclic voltammetry,and copper nanoparticles were then electrodeposited onto the rough surface of the PEDOT/GO nanocomposite through electrochemical reduction in a solution containing copper cations.The modified electrode was used for reliable nonenzymatic electrochemical detection of glucose,and under optimized conditions,it exhibited a high sensitivity up to 909.1 μA/mM/cm2 and a very fast response time of less than 1 s,with a wide linear range of 0.1 μM to 1.3 mM and a low detection limit of 47 nM.This nonenzymatic glucose sensor was,furthermore,highly stable and unresponsive to potentially interfering substances,and it could be used for the assay of glucose in real human serum samples.These enhanced sensing performances were ascribed to the close contact of copper nanoparticles onto the rough surface of the PEDOT/GO conducting polymer nanocomposite,which has good conductivity and very high surface area that can act as excellent substrate for the growth and support of copper nanoparticles.All these results indicate that this electrochemical sensor is highly promising for nonenzymatic glucose detection.(2)A facile two-step electrochemical strategy was reported to synthesize nanocomposite of reduced graphene oxide(RGO)doped conducting polymer poly(3,4-ethylenedioxythiophene)(PEDOT)decorated with nickel nanoparticles(NiNPs)onto a glassy carbon electrode(GCE).Pure graphene oxide(GO)doped PEDOT composite was firstly electropolymerized onto the GCE through cyclic voltammetry,followed by electrochemical reduction in a solution containing nickel cations at a constant potential of-0.9 V.During the electrochemical reduction process,GO doped in the PEDOT composite would be reduced to a more conductive form of RGO,and at the same time,nickel cations could be reduced to form NiNPs and loaded on the composite surface.The prepared nanocomposite(NiNPs/PEDOT/RGO)modified electrode showed outstanding electrocatalytic activity towards the oxidation of glucose in alkaline media,and it could be developed into a nonenzymatic glucose sensor.Under optimum conditions,the glucose sensor exhibited a linear range from 1.0μM to 5.1 mM and a detection limit of 0.8 μM(S/N=3),associated with excellent stability,high reproducibility and favorable selectivity against common interferents.Furthermore,the nonenzymatic sensor was also successfully applied to the detection of glucose in human serum samples,showing promising potential in the clinical application.(3)Conducting polymer polyaniline(PANI)nanowire arrays were electrochemically in situ synthesized on the surface of glassy carbon electrodes,which were modified with self-assembled multi-walled carbon nanotubes(CNTs)networks.The ordered PANI nanowire arrays and CNTs networks were integrated to create 3D nanostructured PANI/CNTs composites.Owing to their unique microstructure and conductivity,the PANI/CNTs nanocomposite exhibited excellent electrical properties such as remarkable supercapacitor performance and catalytic activity toward nitrite electrochemical reduction.It was found that the PANI/CNTs nanocomposite was capable of delivering high specific capacitance and showed excellent cycling stability.Moreover,it could be utilized as an electrochemical sensor for the detection of nitrite,with an outstanding sensitivity,low detection limit(6.08 μM,a signal to noise ratio of 3)and a fast response time of less than 5 s.(4)Biofouling arising from nonspecific adsorption is a substantial outstanding challenge in diagnostics and disease monitoring,and antifouling sensing interfaces capable of reducing nonspecific protein adsorption from natural complex media are highly desirable.We present herein,the preparation ofnovel composite nanowires through the grafting of polyethylene glycol(PEG)polymer onto polyaniline(PANI)nanowires,and their application in the development of antifouling electrochemical biosensors.The PEGylated PANI(PANI/PEG)nanowirespossessed large surface area and remained conductive,and at the sametime demonstrated excellent antifouling performancesinsingle protein solutions as well as complex human serum samples.Sensitive and low fouling electrochemical biosensors for breast cancer susceptibility gene(BRCA1)can be easily fabricated throughthe attachment of DNA probes to the PANI/PEG nanowires.The DNA biosensor exhibited a high sensitivity to BRCA1 with a linear range of concentrations from0.01 pM to 1 nM,and it was also efficient enough to detect DNA mismatches with satisfactory selectivity.Moreover,the DNA biosensor based on the PEGylated PANI nanowires supported the quantification of BRCA1 in complex human serum,indicating great potential of this novel biomaterial for application in biosensors and bioelectronics.(5)A highly selective miRNA biosensor was successfully constructed by introducing the thiol-terminated material(peptide sequence,polyethylene glycol and Mercapto alcohol)onto the surface of polyaniline modified electrode.For the three kinds of antifouling materials used in this study,the designed and synthesized peptides can effectively reduce the non-specific adsorption of proteins,and its antifouling ability can be comparable with polyethylene glycol.For the four kinds of miRNA biosensors,the DNA/Pep/PANI/GCE shows the highest specificity for single base mismatch,three base mismatch and completely complementary miRNA.The experimental results show that the addition of antifouling material does not significantly change the sensitivity of the sensor.These thiol containing antifouling materials also have the potential to be used for the development of other sensors.