Surface-enhanced Raman Spectroscopy Identification Of Glucose Enantiomers By Phenylalanine-modified Gold Nanoparticles

Enastereomerization is a ubiquitous phenomenon in chemistry,where one enantiomer and the corresponding one are identical in many properties.However,their differences in efficacy in biological systems have attracted great attention,making the identification of enantiomers an important task in a wide range of fields,including drug screening,diagnosis,and environmental monitoring.Circular dichroism(CD)is a common method for enantiomer resolution,which usually requires a higher sample concentration or a longer optical path to obtain observable enantiomer signals.More importantly,CD testing will fail for samples at lower concentrations.Therefore,it is necessary to find other spectral methods to overcome the shortcomings of CD spectral technology.We found that there are differences between enantiomers when interacting with certain chiral molecules.For this purpose,the key is to effectively observe these differences by appropriate spectral analysis methods.In this respect,Surface-enhanced Raman scattering(SERS)is a field worth paying attention to.SERS method has many advantages,such as fast detection speed and sensitive detection,it is highly sensitive to the interaction between molecules by monitoring the fingerprint information changes of molecular vibration.D-glucose(D-G)and L-glucose(L-G)enantiomers were selected as research objects.The CD spectral signal of low concentration of D and L-glucose is very weak,leading to no response of CD spectral detection.D-glucose is preferred and L-glucose is excluded in most organisms,and this phenomenon of chiral selection is one of the unsolved scientific puzzles related to the origin of life.In view of the unique biological function of glucose,it is of great significance to establish a method to distinguish and detect glucose enantiomers.Therefore,the following research(chapter 2～chapter 4)were carried out.In chapter 2,gold nanoparticles(Au NPs)with average particle size of 40nm were prepared by surface modification of Au nanoparticles with L/D-phenylalanine(phe).Au-L/D-phe nanoparticles was synthesized as SRES substrates to selectively distinguish D/L-glucose.Au-L-phe can distinguish glucose enantiomers successfully.The signal intensity(I1000)of Au-L-phe at 1000 cm-1 is 1.6 times stronger than that of Au-L-phe,and the signal intensity of Au-L-phe L-G is 3.5 times weaker than that of Au-L-phe.There was a good linear relationship between the overmagnitude of glucose enantiomer and I1000.But Au-D-phe cannot distinguish between glucose enantiomers.CD detection at the same concentration could not distinguish glucose enantiomers,which reflected the advantage of SERS.In chapter 3,by adding phenylalanine surface modifier and using sodium borohydride reducing agent,L-phe-au and D-phe-au nanoparticles with average particle size of about 5 nm were successfully prepared,and then self-assembled with 40 nm gold nanoparticles to form Au-D/L-phe-Au satellite structure as SERS substrate for selective recognition and quantitative detection of glucose enantiomers.Au-L-phe-Au and Au-D-phe-Au can also distinguish glucose enantiomers and be used to detect glucose in saliva of actual samples with a minimum detection concentration of 5×10-8 mol/L.Based on the above research and test,this method provides a new method for the detection of glucose chirality.In chapter 4,phenylalanine and p-mertophenylboric acid(PMBA)were modified onto 40 nm gold nanoparticles.The two molecules were modified together,and the SRES signal was successfully enhanced.Glucose enantiomers were further distinguished by SRES,and glucose enantiomers were successfully distinguished by signal intensity differences at the characteristic peaks of PMBA.The minimum detection concentration was reduced to 5×10-10 mol/L and had a good linear relationship(5×10-4 mol/L-5×10-10 mol/L),realizing the discrimination of glucose enantiomers and further expanding the method of glucose enantiomers.In short,the distinction of glucose enantiomers was realized in this work,and it was found that the surface composition and structure of gold nanoparticles have an important influence on the distinction and detection effect of enantiomers.This will have a great development prospect in the future biomedical pharmaceutical disease diagnosis research.