MXene/Pd-Based Multilayer Composite Films For Electrochemical Detection Of Medicinal Natural Compounds

As a general name of a class of multifunctional two-dimensional transition metal carbide or nitride,MXene has been proved to be a kind of electrochemical sensing material with great advantages and potential due to its large specific surface area,excellent metal conductivity,various adjustable functional groups and open interlayer channels.MXene presents an accordion-like multilayer structure,which can provide more attachment sites for the testing sample,so as to achieve efficient mass charge transfer.However,MXene interlayer nanosheets tend to self-stack due to the van der Waals forces and gravity,which will hinder electron transfer and reduce original electrochemical performance.Due to Pd nanoparticle has excellent catalytic activity,stability and machinability,it has attracted extensive attention in the fields of electrocatalysis and electrochemical sensing.The introduction of Pd nanoparticles on the surface and interlayer of MXene nanosheets not only prevents the self-stacking phenomenon,but also improves the catalytic and electrochemical sensing performance of MXene/Pd-based multilayer composites.The overall stability of the composites can be improved by selectively introducing carbon materials or conductive polymers with good film forming properties,so as to design MXene/Pd-based multilayer composite films with rich functional properties,and realize its application in the electrochemical detection of medicinal natural compounds.Therefore,three kinds of MXene/Pd-based multilayer composite films were designed and prepared by the main material（MXene/Pd）in this paper,which were used to construct three kinds of electrochemical sensing platforms,and systematically studied their sensing performance for electrochemical detection of medicinal natural compounds.The specific contents are as follows:1.Firstly,MXene-Pd nanocomposites were prepared via heating reflux method,where MXene（Ti₃C₂T_x）,Pd nanoparticles and graphene oxide（GO）as raw materials.The rGO/MXene-Pd/rGO hierarchical film was prepared by dropping coating GO,MXene-Pd and GO respectively,and electrochemically reducing GO to reduce graphene oxide（rGO）.The hierarchical rGO/MXene-Pd/rGO film has large specific surface area and good catalytic activity.Under optimal conditions,the rGO/MXene-Pd/rGO/GCE showed a good line response to luteolin in the range of0.6 n M-0.8μM and 1μM-10μM,with a low detection limit of 0.2 n M and a high sensitivity of 112.72μA?μM^-1?cm^-2.In addition,the designed sensor displays high selectivity,reproducibility and repeatability for the detection of luteolin,and has been successfully applied to the detection of luteolin in honeysuckle.2.PEDOT:PSS/MXene-PdAu/PEDOT:PSS sandwich films with good conductivity,stability and catalytic activity were prepared via following two steps:First,MXene-PdAu composites were regarded as the stuffing,which were prepared by loading PdAu nanoparticles onto the surface and interlayer of MXene nanosheets using one-pot method.Then,poly（3,4-ethylenedioxythiophene）:poly（styrenesulfonate）（PEDOT:PSS）with good film-forming properties was used as the upper and lower layer.The sandwich structure facilitates that PEDOT:PSS film can permeate between MXene-PdAu composites and contribute to the continuity of MXene-PdAu particles,forming a complete conducting three-dimensional framework.Theconstructedelectrochemicalsensorwith PEDOT:PSS/MXene-PdAu/PEDOT:PSS sandwich film was used for the electrochemical detection of shikonin.Under optimal test conditions,the sensor showed a good line response to shikonin in the range of 1 n M-35μM,the detection limit of 0.33 n M and the sensitivity of 5.685μA?μM^-1?cm^-2.Meanwhile,the sensor has good anti-interference ability,repeatability and reproducibility for the detection of shikonin.In addition,the sensing platform was successfully applied to the detection of shikonin in Lithospermum erythrorhizon,indicating that PEDOT:PSS/MXene-PdAu/PEDOT:PSS sandwich film has a good application prospect in the qualitative and quantitative analysis of shikonin.3.Flexible PEDOT:PSS/MXene-Ru/PEDOT:PSS free-standing film were prepared by vacuum filtration technique.The intermediate MXene-Ru composite is completely wrapped by PEDOT:PSS,showing a complete sandwich structure.The free-standing film solves the water dispersion problem of MXene-Ru,while improving the stability and flexibility.Under optimal conditions,PEDOT:PSS/MXene-Ru/PEDOT:PSS free-standing film showed good linear response to detection of shiktin in the range of 9 n M-45μM,and the detection limit was 3 n M.In addition,the free-standing film showed good stability,repeatability and reproducibility,indicating that the PEDOT:PSS/MXene-Ru/PEDOT:PSS free-standing film provides a feasible idea for the field detection of shikonin.