A Chiral Discrimination Method Of Amino Acids Based On Charge Transfer-Induced Surface-Enhanced Raman Scattering Spectroscopy

Amino acids are important organics and play an important role in our lives.All amino acids except glycine contain chiral carbon atoms show optical activity.Amino acids also play an important role in regulating gene expression and cell metabolism.So the detection of amino acid enantiomer in human body is of great significance in health evaluation.In this work,the Ag-TiO2-Ag sandwich Surface-Enhanced Raman Scattering(SERS)substrate was prepared and decorated with single thiol-beta-cyclodextrin and p-aminothiophenol(PATP)by the Ag-S covalent bond to form the chiral discrimination sensor,and then it interacted with different chiral amino acids.Due to the chiral selection of the cyclodextrin,the amino acids enantiomers interacted with the cyclodextrin on the chiral sensor through different hydrophobic effect and intermolecular hydrogen bonds,leading to the difference of hydrogen bonds formed by the amino acid enantiomers and the PATP molecules.The difference of hydrogen bonds formed by different chiral amino acid enantiomers and PATP molecules led to different charge transfer(CT)in different chiral systems,leading to the changes in the relative intensities of the SERS spectra of PATP.The amino acid enantiomers were thus distinguished,and the L-amino acid was selectively discriminated by our chiral discrimination sensor.In chapter 1,the significance of chiral discrimination of amino acids and the main methods of chiral discrimination,separation and detection were first summarized.Then we introduced the principle,advantages and application of SERS technology.Finally,the design idea and significance of this work were expounded by comparison with the traditional discrimination and detection methods.In chapter 2,we introduced the preparation methods of Ag-TiO2-Ag sandwich SERS substrate and chiral discrimination sensor.Then they were characterized by scanning electron microscopy,transmission electron microscopy,UV spectrum and Raman spectrum.In chapter 3,we investigated the ability of enantiomer recognition of the chiral discrimination sensor on the basis of the difference of the SERS spectra of PATP in different chiral systems,and proposed the possible discrimination mechanism.In chapter 4,we summarized the method of chiral discrimination of amino acids based on CT-induced SERS spectroscopy.L-enantiomers of tryptophan,phenylalanine and tyrosine were selectively distinguished with different concentrations by this chiral discrimination sensor,and the lowest detection concentration of L-tryptophan reached 1.0×10-7 mol/L.Moreover,the recognition of L-tryptophan in the racemic tryptophan system was achieved with high sensitivity by this sensor.Our results indicated that this chiral discrimination sensor exhibited universality and high sensitivity.