Enhanced Raman Mechanism, Enzyme-like Properties, And Applications Of Polyoxometalates-based Substrates

Polyoxometalates（POMs）are clusters that are located between atoms,molecules and nanomaterials,exhibiting defined atomic composition,electronic configuration,geometric structure,and well-defined surface ligands.The binding sites and adsorption orientations between probe molecules POMs are fixed,making cluster-enhanced resonance Raman spectroscopy（CERRS）crucial for investigating the interactions between clusters and molecules..Due to their structural diversity and unique properties,POMs have garnered significant attention in fields such as catalysis,supramolecular assembly,biomedicine,sensing,and data storage.The lacunary POMs can alter their chemical properties,facilitate charge transfer of reactions,and modify the catalytic process.Metal@lacunary POMs nanoclusters exhibit advantages such as excellent monodispersity,good biocompatibility,strong surface-enhanced Raman spectroscopy（SERS）activity,and high catalytic activity.In this thesis,we explore the cluster resonance-enhanced Raman mechainsm for probe molecules using POMs as the Raman enhancement substrate.In addition,the lacunary POMs complex was constructed to investigate their SERS enhancement properties and the catalytic mechanism of peroxidase-like activity,with applications in biomedical detection.The main research contents of this thesis are as follows:（1）We have discovered for the first time that POMs clusters possess the admirable activity to enhancing the Raman spectrum of crystal violet（CV）molecules,exhibiting high detection sensitivity.We term this enhancement as cluster-enhanced resonance Raman spectroscopy（CERRS）.Through calculations,we determined that the Raman enhancement factor generated by one POMs cluster is 1.85×10².In addition,we investigated the charge transfer degree of the CV-POMs system and synthesized CV-POMs crystals.By analyzing the single crystal structure parameters through single-crystal X-ray diffraction,we inputted the data into Gaussian for density functional theory（DFT）calculations.We found that CV-POMs possess a wider energy gap,indicating higher kinetic stability.The electronic cloud density of CV exhibited significant changes,indicating charge transfer between CV-POMs systems yielding improved CERRS effects.This study provieds new insights into the analysis of surface-enhanced Raman spectroscopy and paves the way for a better understanding of the Raman enhancement mechanism at the cluster level.（2）We synthesized lacunary-POMs including Na₇PMo₁₁O₃₉ and Na₇PW₁₁O₃₉,and further constructed Au@Na₇PMo₁₁O₃₉ and Ag@Na₇PW₁₁O₃₉ nanoclusters by using Na BH₄ reduction method.Due to the differences in the number of negative anions and p H environments of lacunary POMs clusters,altered their surface electronic structures and energy bands,facilitating charge transfer between POMs and probe molecules.In addition,the formed nanoclusters had sizes within the range of surface plasmon resonance（SPR）,thereby enhancing their SERS enhancement capability.Furthermore,the peroxidase-like catalytic activities of Au@Na₇PMo₁₁O₃₉ and Ag@Na₇PW₁₁O₃₉ nanoclusters were enhanced by SPR induction.Therefore,Au@Na₇PMo₁₁O₃₉ and Ag@Na₇PW₁₁O₃₉ nanoclusters provided a new insight into the mechanism of SERS enhanced and nanozymes catalysis.It provides a novel approach for constructing a simple,low-cost,and highly sensitive detection platforms based on nanoclusters SERS enzyme catalysis.（3）Ag@Na₇PW₁₁O₃₉ exhibits good monodispersity,biocompatibility,and effective electrostatic adsorption with antibody molecules.We incubate Ag@Na₇PW₁₁O₃₉-antibody with different concentrations of antigens on an ELISA-microplate,and compared the intensity of SERS signal generated by the catalytic oxidation of OPD by different concentrations of Ag@Na₇PW₁₁O₃₉nanozymes,achieving high-sensitivity of nanozyme-linked immunosorbent assay for immunoglobulin G（Ig G）.（4）Exosomes can carry rich molecular information about tissues and cells,making them potential biomarkers for malignant tumors.We developed Fe₃O₄@SiO₂ magnetic nanoparticles with moleculary imprinted polymers（MIP）for exosome recognition.These particles were used to enrich exsomes from urine samples.CD9 antibodies were labeled with Au@Na₇PMo₁₁O₃₉ and specifically recognized the Fe₃O₄@SiO₂ magnetic nanoparticles enriched with exosomes.After magnetic separation,the Au@Na₇PMo₁₁O₃₉-antibody-exosome-Fe₃O₄@SiO₂complex was obtained.Au@Na₇PMo₁₁O₃₉ catalyzed the oxidation of the substrate molecule TMB,and the quantity of exosomes in urine can be indirectly determined based on the varying SERS intensity of the oxidized TMB.This novel exosome detection method enables rapid and ultrasensitive differntiation of the therapeutic status of both healthy individuals and pancreatic cancer patients.This biosensor based on NELISA-MIPs-SERS,provides a new avenue for early cancer screening by detecting exosomes.