Peptide Mediated COF Nanoenzyme Catalytic Amplification And Nano Plasma Spectrometric Detection Of Trace Cd²⁺and Cu²⁺

Covalent organic frameworks（COFs）are new crystalline porous materials composed of light elements connected by stable covalent bonds,which show excellent potential in gas storage and separation,small molecule adsorption and catalysis.COF synthesis can be carried out by many methods,such as solvothermal method,ionothermal method or microwave chemistry.However,most of these methods require relatively harsh experimental conditions and long COF crystallization time.As an attractive synthesis method,room temperature mechanochemical grinding and hydrothermal method provided convenience for the preparation and wide application of COF.With the development of COF design and synthesis,it had shown great potential in analytical chemistry,and new methods of COF photometry,fluorescence,electroanalysis,chromatography and SERS（Surface Enhanced Raman Scanning）nano analysis were constructed.Soluble starch（SS）is a common natural polydextrose.In natural starch,amylose accounts for 20%～26%,which is soluble,and the rest is amylopectin.Amylose has attracted the attention of researchers because of its special temperature variation properties.Signal catalytic amplification has a decisive influence on the sensitivity of the analytical method.The preparation of highly efficient and stable nano-catalyst and its application in molecular spectral analysis has been a research hotspot.Therefore,this subject organically combines the specific and inexpensive peptide small molecule biosensor recognition technology with COF nanoenzyme catalytic amplification technology,and establishes a detection method for the determination of trace Cd²⁺and Cu²⁺by peptide mediated COF nanoenzyme catalytic amplification-nanogold plasma sol SERS/RRS（Resolution Rayleigh Scattering）/Abs（Ultraviolet Absorption）.COF and nano-enzyme materials were investigated by molecular spectroscopy,particle size analysis and transmission electron microscopy,and a reasonable catalytic mechanism was proposed.The details are as follows:Under normal temperature conditions,with ethanol as the solvent,2,4,6-trihydroxy-1,3,5-benzenetricarboldehyde（Tp）,benzidine（BD）,benzene-1,3,5-tricarboldehyde（BTCA）,1,3,5-tris（4-aminophenyl）benzene（TAPB）and 2,5-dimethylterephthaldehyde（DMTP）as the precursors,the covalent organic framework COF_TpBD/COF_TB/COF_DT with high catalytic performance was synthesized by stirring method.The change rule of its catalytic performance was studied by HAuCl₄-CHOONa（Fo）reaction.The results showed that COF_TpBD had the strongest catalytic activity.The gold nanoparticles（AuNPs）generated by the nano catalytic indicator reaction have high SERS/RRS/Abs signals.It was found that Cu²⁺RK polypeptide(RNRHTHLRTRPRK,PT_RK)was adsorbed on the surface of COF_TpBD,blocking its redox electron transfer,thereby inhibiting the occurrence of HAuCl₄-Fo reaction.When Cu²⁺was added,it can form stable complexes with PT_RK,and the catalytic effect of COF_TpBD was restored;With the increasing concentration of Cu²⁺,the catalytic action gradually recovered and the AuNP generated gradually increased.The indicator component AuNP could be used as the active substrate of SERS.After the VBB probe molecule was added,the SERS signal intensity increased linearly at 1617cm^-1;At the same time,the RRS signal strength at 370 nm also increased with the increasing number of AuNPs generated;The SPR absorption value at 540 nm had a linear relationship with Cu²⁺concentration.So as to achieve the purpose of detecting Cu²⁺.The established RRS and SERS analysis methods were applied to the actual environmental water detection,and achieved good results.SS was loaded onto the covalent organic framework COF_TpBD/COF_TB/COF_DT to prepare COF_TpBD-SS/COF_TB-SS/COF_DT-SSmaterials with high catalytic performance and strong stability.It was found that COF_TpBD-SS had a strong catalytic effect on the indicator reaction of HAuCl₄oxidation of Fo to produce oxidation product AuNPs.The catalytic enhancement mechanism of COF_TpBD-SS was analyzed.This is because COF_TpBD-SS has largeπbonds and is rich inπelectrons,which greatly promotes the electron transfer of HAuCl₄-Fo oxidation-reduction reaction,so COF_TpBD-SS has high catalytic performance.When Cd²⁺is added,the cadmium ion CW polypeptide（Csy-Pro-Cys-Trp-NH2,PT）,the amino acid residues on the peptide chain-COOH combine with Cd²⁺to form a complex,enhance its redox electron transfer,accelerate its catalytic action,and lead to an increase in the concentration of AuNPs.After adding VBB（Victoria blue B）signal molecules,AuNPs as SERS substrate can generate SERS signals,which change with the concentration of AuNPs.Based on the change of SERS signal with Cd²⁺concentration,the SERS analysis method of Cd²⁺was established.Similarly,the Abs analysis method of Cd²⁺was also constructed.By coupling SERS and Abs analytical methods,the sensitivity and reproducibility of the analytical method can be improved.A SERS-Abs dual-mode analytical method for the detection of Cd²⁺is established,with a linear range of 0.025-0.95 nmol/L and a detection limit of 0.012 nmol/L.Through the investigation of interference ions and the detection of actual samples,the content of Cu²⁺/Cd²⁺in water samples ranges from 0.0473 to 0.088 nmol/L and 0-0.31 nmol/L,while the content of Cu²⁺/Cd²⁺in food ranges from 1.27 to 2.15 ng/g and 0-12.21 ng/g.This method is practical and feasible,providing a reference for analytical methods for detecting trace inorganic pollution in the environment.