A Label-free Surface-enhanced Raman Scattering Method For Recognition Of Chiral Aromatic Small Molecules

Chiral aromatic small molecules are generally the important reactants or intermediates of the products in the fields of catalytic chemistry,pharmaceutical engineering,food science,etc.Different enantiomers of a single kind of chiral molecule have different physical and chemical properties,reactivity,and catalytic activity.Therefore,chiral discrimination on aromatic molecules is of great significance particularly in chemical synthesis and industrial production fields.Although a variety of methods have been proposed for chiral discrimination,developing an efficient and universal chiral discrimination approach remains an urgent issue.Surfaceenhanced Raman scattering(SERS)technology is widely used in molecular detection and structural analysis because of its single-molecule detection sensitivity and ability to provide molecular structure information.The alkylthiol self-assembled membrane is capable of pulling the target molecules into the ordered molecular chain,which is favorable to realize the determination of the target analytes.In this thesis,we proposed a label-free method for discrimination of chiral aromatic molecules based on SERS spectroscopy.The chiral recognition sensing system was constructed by decorating a self-assembled n-hexyl mercaptan as capture membrane and a layer of p-mercaptophenylboronic acid as a chiral sensor on the ordered gold nanorod array substrate.The chiral aromatic small molecules were thus discriminated on the light of the changes of the SERS patterns when different chiral molecules were involved into the sensing system.In chapter 1,the significance of chiral discrimination on aromatic small molecules and recognition and detection methods were summarized firstly.Secondly,we introduced the principle of SERS spectroscopy,the characteristics and preparation methods of SERS array substrate,and the advantages of SERS technology on molecular recognition.Then,the construction method,significance and application of molecular self-assembled monolayers were reviewed.Finally,the innovation and significance of this work were proposed with the comparison of traditional chiral recognition methods.In chapter 2,we introduced the preparation method of ordered gold nanorod array substrate.Then,absorption spectroscopy,transmission electron microscopy,scanning electron microscopy and SERS were used to characterize the prepared array substrate.After optimizing the preparation conditions,a chiral discrimination sensing system with good recognition ability for aromatic chiral small molecules was constructed.In chapter 3,by comparing the recognition ability of chiral discrimination sensing system under different pH conditions,the influence of pH on the chiral discrimination ability of the sensing system was investigated and the pH conditions were optimized for an efficient chiral discrimination.Then,we investigated the universality of the chiral discrimination sensing system,and proposed the possible mechanism for the discrimination.In chapter 4,we summarized the proposed chiral discrimination method for aromatic small molecules based on the label-free SERS spectroscopy.