Enantiomer Identification Based On Raman Spectroscopy And Chiral Silicon-based Composites

In previous studies,by referring to the synthesis method of the mineralization process of biological silica gel and controlling the hydrolysis and condensation process of SiO₂precursors,the chirality of chiral biomimetic polymer was transferred to inorganic SiO₂to make it chiral.Chiral SiO₂nanofiber materials(including D-SiO₂and L-SiO₂)with high temperature resistance(about 900?)were obtained.This kind of SiO₂did not possess chiral characteristics in structure,but it showed chiral optical activity signal of Si-O chemical bond within 200 nm on the circular dichromatic spectrum(CD),and it could induce various organic and inorganic components to produce optical chiral activity,further realizing chiral transfer,which was expected to be used in chiral recognition.Raman spectroscopy is a fast,sensitive and relatively accurate detection method,among which Surface Enhanced Raman Scattering Spectroscopy(SERS)has the detection sensitivity of single molecule level.They can both provide abundant molecular structure fingerprint information,and both have great application potential in the application of chiral enantiomer recognition.In this paper,using chiral SiO₂nanofibers as chiral source and carrier,a series of chiral selective Raman substrates were constructed to induce pairs of enantiomers to generate differentiated Raman scattering signals,thus realizing the selective recognition of enantiomers by Raman spectroscopy.This paper mainly includes the following contents:(1)In work 1,Chiral D-SiO₂/PDA and L-SiO₂/PDA composite Raman substrates were prepared by modifying the surface of polydopamine(PDA)chiral SiO₂nanofibers.When D-SiO₂/PDA(or L-SiO₂/PDA)interacted with a variety of amino acid enantiomers(cysteine,cystine,phenylalanine and tryptophan),The Raman signal intensity of amino acid enantiomers is significantly different,and the difference can be more than two times,so the selective identification of enantiomers can be realized by Raman spectroscopy.In contrast,DL-SiO₂/PDA(racemic)synthesized from acchiral SiO₂did not have similar recognition effect.At the same time,these amino acid enantiomers can in turn act as chiral indicators of SiO₂,which can be explained by the unique mirror image relationship derived from Raman spectroscopy.Therefore,this paper also established an indirect method to detect the chirality of inorganic nanomaterials.(2)Since chiral SiO₂/PDA composites could not identify amino acid enantiomers with low Raman activity well,in work 2,silver(Ag)nanoparticles were reduced in situ on its surface to construct the precious metal SERS substrate,and then detached from silica to form PDA/Ag composites.The as-obtained PDA/Ag showed surface-enhanced Raman scattering(SERS)activity but very weak circular dichroism optical activity.Interestingly,the PDA/Ag substrates could make a pair of tyrosine(or phenylalanine)enantiomers show different Raman scattering signal intensities,where the differences could reach 3 times.In contrast,PDA/Ag prepared by using racemic or achiral silica did not exhibit such discrimination performance.Therefore,this research offered a novel SERS-based enantiomeric differentiation method with the assistance of plasmonic metal-containing substrates stemmed from intrinsically chiral inorganic silica.(3)As the precious metals SERS substrate had the disadvantages of instability and inhomogeneity,in order to avoid this deficiency,in work 3,the conductive polymer PPY was introduced on the surface of chiral SiO₂at the same time,so that PDA and PPY could have a synergistic effect with chiral SiO₂,enhancing the Raman response performance and reducing the detection limit of cysteine and phenylalanine.The research in this paper is expected to expand the application range of Raman spectroscopy in the field of chiral recognition,and also contribute to the in-depth understanding of the molecular structure of inorganic SiO₂from the perspective of chirality,and provide new ideas and ideas for the study of enantiomer recognition.