The Study Of Novel Electrochemical Sensors Based On Plant-derived Three-Dimensional Porous Carbon

Electrochemical sensor is a kind of sensing device based on electroactive materials(such as enzymes,electron mediator,etc.)as the sensitive elements to transform the electrochemical signal and shows high sensitivity,good selectivity,rapid analysis speed,simple operation,easy miniaturization,on-line detection,etc.However,enzyme and electron mediator easily aggregated on the electrode surface to lose their activity and falled off from the electrode surface.Therefore,how to keep their electroactivity and how to increase the amount of electroactive materials on electrode surface have become hot topics.In addition,for the traditional electrochemical sensor,how to improve the repeatability of the electrode is another difficulty to overcome.In this thesis,we used three-dimensional kenaf stem-derived biological carbon as supporting materials,used metal-organic framework to load enzyme and electron mediator for preparing electrochemical sensor and ratiometric electrochemical sensors or used covalent organic frameworks to load metal nanomaterials to build the nonenzymatic electrochemical sensor,and they were successfully used in hydrogen peroxide,ascorbic acid and glucose detection.The main works included the following five parts:1.A novel hydrogen peroxide(H2O2)biosensor was developed based on the microperoxidase-11(MP-11)encapsulated in metal-organic frameworks(MOFs),PCN-333(Al)(PCN stands for porous coordination network),which was firmly and uniformly grew on the three-dimensional(3D)kenaf stem-derived porous carbon(3D-KSC).The ball-flower-like PCN-333(Al)with mesopores of 5.5 nm was especially suitable for encapsulating MP-11(1.1×1.7×3.3 nm).Scanning electron microscopy and energy disperse spectroscopy were used to characterize the 3D-KSC electrode and the 3D-KSC/PCN-333(Al)@MP-11 electrode.UV-Vis spectroscopy was used for characterizing the encapsulation of MP-11 in the 3D-KSC/PCN-333(Al)electrode.Cyclic voltammetry and differential pulse voltammetry were used to characterize the electrochemical behaviors and performance of the biosensor.The results showed that the encapsulated MP-11 molecules showed a better performance than free enzyme.Under the optimized experimental conditions,the resulted H2O2 biosensor exhibited a wide linear range from 0.387 ?M to 1.725 mM,a low detection limit of 0.127 ?M with good stability and high selectivity,which was superior to some other biosensors.2.A novel ascorbic acid(AA)ratiometric biosensor was prepared by using the PCN-333(Al)MOFs to encapsulate Ketjen black(KB)as catalyst for catalyzing oxidation of AA and thionine(Thi)as an internal reference signal simultaneously.The encapsulation of KB and Thi in the pores of PCN-333(Al)MOFs not only improved efficiency of KB and Thi greatly because PCN-333(Al)MOFs could effectively avoid the cohesion or aggregation of KB and Thi on electrode surface but also enhanced the stability of biosensors because they were immobilized in the pore firmly.Furthermore,PCN-333(Al)MOFs could also selectively accumulate target analytes into their pores to enhance the selectivity of biosensors.The oxidation peak current of AA catalyzed by KB at-0.05 V increased with the increasing concentration of AA,while the oxidation peak current of Thi at-0.24 V kept constant,which resulted in a novel ratiometric biosensor for AA detection.The ratiometric biosensor exhibited a wider linear range from 14.1±0.2 to(5.5±0.1)?103 ?M(R2=0.998)and a lower detection limit of 4.6±0.1 ?M with high accuracy,selectivity,reproducibility and sensitivity.The ratiometric electrochemical approach is not only a new method for AA detection but also opens a new way for sensitive detection of other analytes.3.A highly selective and accurate on-off ratiometric electrochemical biosensor to detect glucose was proposed based on gold nanoparticles(AuNPs)-glucose oxidase(GOD)nanocomposites as the catalyst for both the oxidation of glucose and the electrochemical reduction of O2 and the Thi as the inner reference signal for the first time.The reduction peak of O2 catalyzed by AuNPs-GOD at-0.45 V decreased in GOD-glucose reaction in which the O2 was consumed gradually to produce H2O2.While,the reduction peak of the produced H2O2 catalyzed by Thi at-0.24 V increased gradually.By using the ratiometric peak current as detection signal,a novel on-off ratiometric electrochemical biosensor for glucose detection was developed and exhibited an acceptable detection limit of 11.66 ?M and a wide linear range from 35.43 ?M to 15 mM.The biosensor also exhibited high accuracy,high selectivity,good reproducibility and high sensitivity.The ratiometric electrochemical approach not only developed a new method for highly selective and accurate detection of glucose but also provided a good idea for accurate and selective analysis of other analytes.4.It was the first time to combine Cu-BTC MOFs with D-KSC and then electrondepositing AuNPs to form 3D-KSC/Cu-BTC/AuNPs electrode.GOD was immobilized on the surface of the 3D-KSC/Cu-BTC/AuNPs electrode via Au-S bond.The intergrated 3D-KSC/Cu-BTC/AuNPs/GOD electrode was constructed for the ratiometric electrochemical glucose detection.In this study,scanning electron microscopy and energy disperse spectroscopy were used to characterize the 3D-KSC,3D-KSC/Cu-BTC and 3D-KSC/Cu-BTC/AuNPs electrode.Cyclic voltammetry and differential pulse voltammetry were used to characterize the electrochemical behaviors and performance of the biosensor.The reduction peak current density of O2 catalyzed by GOD at-0.45 V decreased and the reduction peak current density of Cu-BTC was increased as the increase of the glucose which was less than 4 mM.However,the reduction peak current density of O2 was still decreased but the reduction peak current density of Cu-BTC was kept constant when the concentration of glucose increased after 4 mM.In order to get a good selectivity and reproducibility,the jO2/jCu-BTC was used as the response signal and exhibited a good linearly with the glucose concentration from 44.9 ?M to 4 mM and the detection limit was 14.77 ?M.The biosensor also exhibited high accuracy,high selectivity and good reproducibility.The ratiometric electrochemical approach not only provides a new method for glucose detection but also opens a new way for sensitive detection of other analytes.5.The graphene-like lamella structured covalent-organic frameworks(COFs)were formed on 3D-KSCs(3D-KSCs/COFs)for electrochemical sensing.By the electrodeposition of CuNPs on the surface of 3D-KSC/COFs integrated electrode,a novel nonenzymatic electrochemical glucose sensor was constructed.The morphology and composites of the 3D-KSCs/COFs and 3D-KSCs/COFs/CuNPs integrated electrode were characterized by scanning electron microscopy and energy disperse spectroscopy.The performance of electrochemical and electrocatalytic behaviors of the 3D-KSCs/COFs/CuNPs electrode towards glucose oxidation were explored by various electrochemical methods.The effect of the concentration of COFs,the electrodeposition time and the catalytic potential on the electrochemical performances were also explored.Owing to its ultra-high mechanical stability and large specific surface as well as the excellent catalytic activity of CuNPs,the glucose sensor based on 3D-KSCs/COFs/CuNPs integrated electrode showed a wide linear range from 6.78 ?M to 22.07 mM and a lower detection limit of 2.23 ?M together with good stability.The results also indicated that the 3D-KSCs/COFs could not only be used to load metal or double metal NPs for the glucose or H2O2 detection,but also as a potential material for a variety of filed such as supercapacitors,biosensor or fuel cells.