Silver Nanowire-based SERS Substrate Design And Its Application In Chiral Recognition

Surface Enhanced Raman Scattering(SERS)spectroscopy has great potential in biological applications.Near-infrared light-excited SERS spectroscopy has many advantages in the analysis of biological tissue samples:biological tissues are relatively transparent in the infrared wavelength range,and can effectively avoid background fluorescence under complex biological conditions,and can limit photobleaching at the same time.Although SERS spectra excited by infrared lasers have great potential in biological applications,it is very necessary to develop SERS substrates with near-infrared activity.Ag nanowires(Ag NWs)can provide relatively high enhancement factors(EF),and its local surface plasmon resonance band is very wide,which can range from near ultraviolet to near infrared.Therefore,silver nanowires are expected to become a substrate with near-infrared SERS activity,providing a new choice for the application of SERS in the field of biomedicine.Chiral molecules are very common in life.In many cases,chiral molecules that are enantiomers of each other will have huge differences in pharmacology,physiological reactions and toxicity.One of the isomers may have great side effects and toxicity,so chiral recognition and separation have become more and more important technologies.Surface-enhanced Raman spectroscopy is expected to become an effective tool in the field of chiral recognition due to its characteristics such as sensitivity,rapidity,and efficiency.However,traditional Au,Ag and other noble metal nanoparticles used as SERS substrates cannot reflect the difference between enantiomers.difference.Therefore,it is necessary to develop a functional SERS substrate with chiral recognition capability.In recent decades,metal-organic frameworks MOFs(Metal-Organic Frameworks)have received extensive attention due to their porous structure,easy functionalization and adjustable characteristics.The organic ligands in the MOF structure bridged with metal ions have been replaced by Organic ligands with chirality can form chiral MOF materials with circular dichroic optical activity,which can be used in asymmetric catalysis,chiral recognition,chiral separation and other fields.Different from traditional SERS substrates,combining chiral MOF with gold and silver nanostructures to form chiral SERS substrates will hopefully enable Raman spectroscopy to be used in the field of chiral recognition.Modification of chiral MOF on the surface of gold and silver nanostructures can also take advantage of the advantages of MOF.In addition to achieving the recognition effect of chiral enantiomers,it can also adsorb molecules to be recognized to the surface of the substrate through its strong adsorption force,which is beneficial to improve the recognition sensitivity of the substrate;by changing the aperture,the recognition of enantiomeric molecules of different sizes can also be achieved.Chiral SERS substrates based on chiral MOF materials provide new research ideas for the development of Raman spectroscopy in the field of chiral recognition.This thesis is based on silver nanowires and explores its application potential in the SERS field.Firstly,the optical properties of silver nanowires are used as a near-infrared active SERS substrate for characterization and SERS performance research.Secondly,the chiral MOF material was modified on the surface of Ag NWs and applied to the enantiomer selection and recognition of chiral molecules.The research contents and results are as follows:1.Ag NWs were prepared by solvothermal method and used as a SERS substrate.A portable Raman spectrometer equipped with a 1064nm laser was used to achieve Raman spectroscopy detection of a variety of molecules,with a detection limit of 0.1mol/L.Combining Ag NWs with 4-mercaptopyridine molecules can also form a p H sensor.In addition,the 633 nm laser can successfully detect the easily carbonized curcumin molecules.In order to give full play to the advantages of the 1064 nm laser Raman,the instrument was applied to skin detection.The pig skin similar to human skin was used to carry out a simulation study,which can successfully realize the detection of the antibiotic molecule gentamicin on the surface of pig skin.This antibiotic molecule is often applied to burn wounds,etc.,and provides support for Raman spectroscopy analysis on skin wounds.2.The commonly used spectroscopy method for chiral recognition is circular dichroism spectroscopy,but this method has certain limitations in sensitivity and molecular specificity,so there is an urgent need to develop efficient,sensitive and convenient enantioselective recognition methods,And the characteristics of Raman spectroscopy just meet the above requirements.Therefore,we chose to use solvothermal method to synthesize chiral metal-organic framework materials in situ on the Ag NWs surface respectively-[Cu-(L-mal)-(bpy)]_n and[Cu-(D-mal)-(bpy)]_n,apply it to the identification of the enantiomers of propranolol hydrochloride,and realize the identification of the enantiomers by observing the characteristic peak-to-peak difference of the enantiomers in the Raman spectrum.And using the pyridine peak of the substrate as the internal standard peak can not only reduce the signal-to-noise ratio at low concentrations,but also make the results more reliable and have good repeatability.3.In order to further expand the Raman spectroscopic recognition window of chiral enantiomers and reduce the difficulty of material preparation,we synthesized another chiral MOF material D-his-ZIF-8 in situ on the Ag NWs surface.The MOF is characterized by mild synthesis conditions and can be formed at room temperature.Through Raman detection of the substrate,it is found that the background peak of the substrate is much less than the characteristic peak of the previous MOF.By constructing the Ag-D-his-ZIF-8 chiral SERS substrate,the successful identification of 1,1'-bi-2-naphthol enantiomer molecules was achieved.