Dopamine Molecularly Imprinted-based MALDI-TOF Mass Spectrometry For Direct Analysis Of Paraquat Histamine And Tryptamine

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry（MALDI-TOF MS）has the advantages of high throughput,high sensitivity,high resolution,rapid detection speed,and small sample quantity,and is widely used for the analysis of macromolecules.However,when used for small molecule detection in complex samples,MALDI-TOF MS is limited by the interference of traditional matrices and sample coexisting substances.With the development of nanotechnology,nano-adsorbents can be used as matrices for the detection of analytes in complex samples by MALDI-TOF MS.These nanomaterials mainly rely onπ-πstacking,hydrogen bond,and electrostatic interaction to adsorb analytes but lack specificity.In addition,most of the reported nano-adsorbents require special functional ligands or post-modifications to achieve good adsorption capacity,leading to a lack of universality.Therefore,this paper aims to address the challenges of instability of MALDI-TOF MS matrices and background interference in complex systems by screening nano-adsorbents with surface molecular imprinting capability as matrices for MALDI-TOF MS.A surface molecularly imprinted MALDI-TOF MS（SMI-MALDI-TOF MS）method was established for rapid,highly sensitive,and specific enrichment and detection of methyl violet,histamine,and tryptamine in complex samples.The specific research contents are as follows:The principles of MALDI-TOF MS and the challenges associated with its application in complex samples were described,and the application of nanomaterials in MALDI-TOF MS was presented.The principles,development,and current research status of molecular imprinting technology were reviewed.The current status of the combined use of molecular imprinting and MALDI-TOF MS was summarized,and the basis and research content of this paper were proposed.This paper combines the molecular specificity and affinity of surface molecularly imprinted polymers（SMIPs）and the high sensitivity detection capability of MALDI-TOF MS.Using C-COFs as the substrate,dopamine as the functional monomer,and methyl violet as the template molecule a surface molecularly imprinted polymer with specific recognition for methyl violet,C-COFs@PDA-SMIPs,was synthesized.The surface molecular imprinting MALDI-TOF MS method was constructed using C-COFs@PDA-SMIPs as an adsorbent and MALDI matrix for the specific enrichment and detection of methyl violet.Materials characterization showed that C-COFs@PDA-SMIPs had strong UV absorption,good thermal stability,and chemical stability.Compared with non-imprinted materials（C-COFs@PDA-NIPs）,the imprinted material had a larger specific surface area and pore size,indicating that the imprinting sites had been formed on the surface of the imprinting material.Furthermore,in order to obtain the best experimental results,the synthesis and enrichment conditions of C-COFs@PDA-SMIPs were optimized.Under optimal conditions,this method could capture PQ quickly and selectively.The detection limit for PQ was as low as 0.8 pg/m L,and the linear range was 5-500 pg/m L.The method was applied to the analysis of actual samples such as herb grass and orange peel,yielding good detection results with recovery rates of 85.87%-112.68%and relative standard deviations of 4.56%-10.93%.The quantitative results for PQ in herb grass and orange peel were consistent with those obtained by LC-ESI-MS.Carboxylated gold nanoparticles were grown on the surface of amino-functionalized silica nanoparticles（Si O₂ NPs）,and using Si O₂@Au as the substrate,dopamine as the functional monomer,and histamine and serotonin as template molecules,a dual-template molecularly imprinted polymer with good biocompatibility and conductivity was synthesized（Si O₂@Au-dual MIP）.The Si O₂@Au-dual MIP showed strong UV absorption in the near-UV region and had good thermodynamic and chemical stability.The synthesis and enrichment conditions of Si O₂@Au-dual MIP were optimized by evaluating the MALDI MS signal intensity as an indicator.Under optimal experimental conditions,Si O₂@Au-dual MIP demonstrated rapid and highly selective adsorption of histamine and serotonin with good linearity in the range of 1-500ng/m L for histamine（R²=0.9917）,and a detection limit of 0.2 ng/m L and RSD of 0.63%-4.62%.For serotonin,the range of good linearity was 0.8-300ng/m L（R²=0.9921）,with a detection limit of 0.1 ng/m L and RSD of 1.36%-7.16%.This method was applied to the analysis of actual samples such as chicken meat.