Construction Of MXene And Its Composites And Investigation On Their Sensing Applications

Electrochemical biosensors illustrate the advantages of easy operation,fast response,highly sensitive detection ability,and good selectivity,thus showing widespread applications for the medical diagnosis,food safety,process control and environmental monitoring.The performance of electrochemical biosensors is usually closely related to the type of electrode material.MXenes possess unique electronic structure and intrinsic electrochemical activity,often utilizing as electrode materials to construct electrochemical biosensors.However,the poor ability of MXenes to immobilize aptamers and low catalytic activity results in the need to improve the sensitivity and output signal of MXene-based electrochemical sensors.In view of the difficulties in the development of MXene-based electrochemical biosensors,MXene-based composites were synthesized by the pyrolysis,structural conversion and functionalization methods,and they were used to construct various sensors to achieve sensitive detection of different pollutants in the environment and food in this dissertation.This dissertation is mainly divided into four aspects:（1）An ultrathin 2D porphyrin–based MOF nanosheets（2D V–PMOF NSs）were in suit synthesized using V2CTx MXene as precursor and meso–tetra（4–carboxyl–phenyl）porphyrin as linking block.An impedance electrochemical aptamer sensor was constructed by immobilizing 17β–estradiol（E2）on the modified 2D V-PMOF gold electrode to achieve sensitive detection of E2.The results show that 2D V-PMOF has abundant defect structure,large specific surface area,good biocompatibility and excellent electrochemical activity,which is conducive to enhancing the immobilize E2-targeted aptamers and improving the signal response of electrochemical aptamer sensor.The developed aptasensor showed the ultralower detection limit of 0.81 fg·m L^–1 within the wider 17β–estradiol concentration range of 10 fg·m L^-1-10 ng·m L^-1 compared to original V2CTx MXene–based aptasensor and other reported E2 biosensors.In addition,the constructed V-PMOF-based aptasensor also exhibits high selectivity and sensitivity for the detection of E2 in real samples.（2）Based on the large surface area and porosity of MOF and MXene,CoZn-ZIF@V2CTx was transformed into heterojunction materials（denoted as VZnCo@MWCNTs）of multicomponent transition metal oxides（Co3O4,ZnO,V2C and V2O5）and multi-walled carbon nanotubes（MWCNTs）by high-temperature calcination method in this chapter.Due to the structural characteristics of VZnCo@MWCNTs,such as rich metal sites,abundant structure defects and element oxygen vacancies,N–doping,large specific surface area and high porosity,a novel dual–modal aptasensing strategy has been established by integrating Zn–air battery（ZAB）–driven self–powered and impedimetric aptasensor based on the VZnCo@MWCNTs heterojunction for the efficient detection of progesterone（P4）from the complex environment.The results show that the developed dual–modal ZAB–driven self–powered and impedimetric aptasensor demonstrated the ultralow detection limit toward P4 of2.12 and 0.76 fg·m L^–1,respectively,within the wide linear range of 10 fg·m L^–1and 0.1 mg·m L^–1.Meanwhile,the dual-mode sensor shows excellent selectivity,sensitivity,repeatability and practical application.The proposed dual–modal aptasensing strategy based on the heterojunction comprised diverse metal compounds can be extended to detect other targets when replacing the corresponding aptamer strands.（3）The prepared ZIF@V2CTx was converted into a heterostructure composite of CoNi layered double hydroxide（CoNi–MLDH）and V2CTx（CoNi–MLDH@V2CTx）by in-situ structure conversion method.Given the merits of V2CTx NSs and advantages of CoNi–ZIF,as well as the synergistic effect of the junction,the gained CoNi–LDH@V2CTx junction had abundant oxygen vacancies and structural defects,which provides a large number of active sites for immobilized aptamers and promotes the ability for oxygen reduction,thus enhancing the output of electrochemical signals.In order to improve the practicability of the ZAB self-powered sensor,a novel dual-mode flexible ZAB self-powered sensor was constructed in this chapter,which realized the sensitive detection of cortisol.The results showed that the impedimetric and zinc-air battery-driven self-powered dual–modal aptasensor illustrated the ultra-low detection limit of 0.26 fg m L^-1 and 0.17 fg m L^-1within a wide detection range from 10 fg m L^-1 to 100 ng m L^-1,respectively.This research lays a foundation for the construction of portable and readable electrochemical sensors.（4）The 2D/2D heterojunction（represented as Cd–MoS2@Ti3C2Tx）in situ prepared by metal sulfides and Ti3C2Tx NSs simultaneously.The gained Cd–MoS2@Ti3C2Tx heterojunction possessed contact interface,hierarchical structure,and plenty of sulfur and oxygen vacancies.Thus,it showed enhanced separation ability of photogenerated electrons and holes and fast electron transfer.A novel photocatalyzed ZAB–based self–powered aptasensor was assembled using Cd–MoS2@Ti3C2Tx as photocathode to immobilized penicillin G（PG）aptamer.The constructed photocatalyzed ZAB displayed a boosted output voltage of 1.43 V under UV-vis light irradiation,and the high voltage response value is conducive to improving the sensitivity and minimum detection limit of the sensor for PG detection.The results show that the constructed ZAB sensor demonstrated an ultralow detection limit of 0.06 fg·m L^–1 within a PG concentration ranged from 1.0 fg·m L^–1 to 100 pg·m L^–1.The present work provided an alternative analysis method for the sensitive analysis of antibiotics based on the portable photocatalyzed ZAB–driven self–powered aptasensor.