Ligand Regulating MXenes Nanocatalytic Amplification-SERS/RRS For The Determination Of Trace Isocarbophos And Imidacloprid

With the continuous development of social economy,the modern agricultural production has also developed rapidly.Pesticides are highly toxic and effective against pests,and are often used as insecticides,acaricides and anti-disease agents in agricultural production,and their widespread use can greatly improve crop yields.However,most pesticides are acutely toxic and carcinogenic,and their residues are constantly transported in the environment and enriched in the human body through the food chain to endanger human health.Therefore,it is important to develop highly sensitive,selective,and inexpensive methods for environmental analysis.Two-dimensional transition metal carbides（MXenes）have good chemical stability,electrical conductivity,and easy surface functionalization.In recent years,MXenes materials have attracted much attention from researchers because of their easy surface functionalization and good electrical conductivity.However,MXenes materials have less application in molecular spectroscopy,especially in Resonant Rayleigh scattering spectroscopy（RRS）and Surface enhanced Raman scattering spectroscopy（SERS）.Therefore,it is of scientific significance to establish analytical methods for trace substances based on the functionalization of MXenes materials and their application to nanocatalytic reactions and RRS and SERS spectroscopy techniques.In this paper,the catalytic properties of doped MXenes materials,ligand（aptamer/peptide）regulation of the catalytic activity of doped MXenes,combined with nanocatalytic reactions,were used to establish a SERS/RRS analytical method for the detection of trace isocarbophos（ICP）in the environment and imidacloprid（IMI）in the vegetable samples.The doped MXenes was characterized and analyzed by transmission electron microscopy,powder X-ray diffraction,X-ray photoelectron spectroscopy and molecular spectroscopy,and the catalytic enhancement mechanism was proposed.Details are as follows:（1）Under microwave-assisted conditions,Ti₃Al C₂ was etched by in situ generation of HF from HCl and Li F to prepare multilayer MXenes nanosheets,and MXene@Au and MXene@Ag nanosols were prepared by CO reduction of HAu Cl₄ and Ag NO₃-doped MXenes,and their effects on the redox reaction of chloroauric acid-mandelic acid（HAu Cl₄-MA）were investigated.The catalytic activity of MXene@Au and MXene@Ag nanosols was investigated.The results of the catalytic mechanism experiments showed that the reductant MA was first oxidized to produce benzaldehyde and finally benzoic acid.Compared with MXenes and MXene@Ag nanomaterials,MXene@Au has abundant surface free electrons to promote the electron transfer of the redox reaction and shows strong catalytic effect on the nano-indicated reaction.When ICP aptamer(Apt _ICP)was added to the catalytic system,it could modulate the catalytic activity of MXene@Au through electrostatic adsorption and then lead to the decrease of SERS/RRS signal.When ICP is added,it can combine with Apt _ICP to form Apt _ICP-ICP complex,thus releasing the free MXene@Au and reactivating the catalytic effect on the nanoindicator reaction to restore the reduced SERS/RRS spectral signal.When the ICP concentration was in the concentration range of 1-25 pmol/L,the RRS signal increased linearly with ICP concentration,whereby the RRS analysis of ICP could be established.The molecular probe Victoria Blue 4R（VB4R）,using the reaction product Au NP as the active substrate for SERS,could produce a SERS signal whose intensity varies with the concentration of Au NP.Therefore,an analytical method for ICP was established based on the law of SERS signal variation with ICP.The method providing a reference for the analytical method of detecting trace isocarbophos in the environment.（2）Imidacloprid peptide modified MXenes-doped bifunctional nanoprobes（TN@Ti MOF/PT）were rapidly prepared under home microwave heating and stirring method assisted conditions,which could catalyze the nanoindication reaction chloroauric acid-glyoxylic acid（HAu Cl₄-GLA）redox system to generate Au NP and specifically recognize the target molecule IMI.However,the catalytic activity of TN@Ti MOF is masked by the modification of IMI peptide(PT_IMI).When the target molecule IMI is added,the recognition of IMI with the specific base sequence of PT_IMI caused PT_IMI to be detached from the surface of the nanomaterial,resulting in the exposure of abundant catalytic active sites,and therefore catalyzing HAu Cl₄-GLA system to form Au NP rapidly.In the concentration range of 0.01-0.25ng/m L,the RRS signal increased linearly with the increase of IMI concentration.Accordingly,the RRS analysis of IMI could be established.Similarly,the addition of VB4R as a molecular probe could generate SERS signal,the intensity of which varies with the concentration of IMI.Therefore,the SERS analysis method for IMI was established based on the pattern of SERS signal variation with IMI concentration.This study can provide a reference for the preparation of bifunctional nanoprobes for trace contaminants.