The Construction And Investigation Of Flexible Electrochemical Sensors Based On Conducting Polymers

The flexible sensor has the characteristics of light weight,good ductility and high adaptability,which can be deformed to fit the skin,and it has attracted much attention of various researchers.Currently,most flexible sensors rely on flexible substrates,using laser engraving or printing technologies to construct sensor parts on flexible substrates.Conducting materials may peel and delaminate from the elastic matrix during mechanical deformation,resulting from difference in modulus between conducting materials and substrates.This seriously affects electrochemical sensors'durability.Using materials with strong stretchability,good flexibility,and high conductivity as flexible self-supporting electrodes to construct sensors can effectively solve this problem.However,the mechanical properties of the materials currently used are poor,and the electrical conductivity needs to be further improved.In this thesis,functional conducting polymers were adopted to construct flexible electrochemical sensors and biosensors.The microstructure,sensing performance and mechanical performance of the constructed sensors were characterized by conventional electrochemical methods and micro-testing characterization methods.The thesis is of positive significance for the design and synthesis of conducting polymer-based composite materials and their application in flexible devices.The main research contents are summarized as follows:(1)An all-polymer-based flexible self-supporting electrode was prepared and used as an electrochemical sensor to detect dopamine(DA).The pyrrole monomer can form a self-supporting film through electrochemical polymerization.The rigid conjugated structure of polypyrrole deteriorates mechanical properties of the film,which limits its application as a self-supporting electrode.The preparation of polypyrrole(PPy)film with excellent mechanical properties and electrical conductivity is essential for its application in flexible electrochemical sensors.We first synthesized highly conducting PEE-PPy film doped with pentaerythritol ethoxylate(PEE)in an organic phase system.Using PEE-PPy and sodium 2-naphthalenesulfonate(2-NS)as working electrode and dopant separately in an aqueous phase system,2-NS-PPy was electrochemically synthesized on the surface of the PEE-PPy film electrode to form a composite film with a sandwich structure.This all-polymer electrode is free-standing and breaks through the bottleneck of traditional flexible electrodes that requires elastic substrates and conducting additives,and it demonstrates high mechanical tensile strength(81.9 MPa),good flexibility(elongation-at-break of 41.6%),and inherent and stable conductivity.When used as an electrochemical sensor for DA detection,this film electrode showed high sensitivity(343.75?A m M^-1cm^-2).Moreover,this all-polymer electrode can bear various deformation(twisting,folding,and knotting)with negligible effect on the sensing performance.This electrochemical sensor maintains 97.3%current response at 25%strain for DA detection.The strong stability(mechanical deformation and long-time storage),in conjunction with superior mechanical property and sensitivity,proves that this all-polymer free-standing film electrode possessed giant potential in the construction of flexible electrochemical sensors.(2)A flexible self-supporting aptamer sensor based on PPy composite film was prepared to specifically detect carcinoembryonic antigen(CEA).Taking advantage of the high conductivity of the film,gold nanoparticles(Au NPs)were electrodeposited on the surface of the PPy composite material,and then aptamer was immobilized by self-assembly through the formation of gold-sulfur bonds.In order to improve the recognition ability of the aptasensor,6-mercapto-1-hexanol was used to block the remaining active sites.The constructed PPy composite film based aptasensor showed excellent sensing ability(as low as 0.033 ng m L^-1),high selectivity and long-term stability(97.1%of the original signal after 15 days).In addition,the mechanical performance of the aptasensor was also tested.The aptasensor could bear various deformations,and different deformations had almost no effect on the sensing signal.It could maintain 99.4%of the original signal under 25%strain.The aptasensor also presented superior sensing performances,excellent mechanical properties and good deformation stability,indicating promising potential in the application as flexible electrochemical aptasensors and implantable devices.(3)The design of wearable sensors for real-time monitoring of biomarkers related to human health is of great significance to human life and health monitoring.Conducting polymer hydrogel has excellent electrochemical properties and flexibility,and it can be used to prepare flexible electrode materials,which is very important for assembling flexible wearable sensors.Poly(3,4-ethylenedioxythiophene)-polyvinyl alcohol(PEDOT-PVA)hydrogel was synthesized herein by chemical oxidation,and it was then combined with MXene to modify the printed electrode.The constructed flexible hydrogel based sensor showed good electrocatalytic performance for the uric acid(UA),with high selectivity and high detection sensitivity(0.289?A?M^-1cm^-2).The synthesized hydrogel also possessed excellent mechanical properties(elongation-at-break of 347.7%),and the sensor signal of the hydrogel electrode showed basically no significant change after deformation.The hydrogel electrode was combined with a designed microfluidic device to construct a flexible wearable sensor,and it was able to sensitively detect UA in human sweat.