Construction Of SERS Substrate Based On MOF Structure And Detection Of Biomarkers In Serum

Surface-enhanced Raman spectroscopy（SERS）is the most versatile and powerful due to its ultra-high sensitivity（single molecule）,unique"fingerprint"specificity,and non-destructive analysis in molecular sensing.These unique advantages make SERS become a promising tool in various branches of analytical science,such as environmental monitoring,food analysis,surface analysis,disease diagnosis,and more.At present,there is no unified view on the enhancement mechanism of SERS.It is generally believed that physical enhancement（EM）and chemical enhancement（CM）work simultaneously in the detection process,but the physical enhancement mechanism dominates.Most of the traditional SERS substrates are metal sols,which are generally prepared by a chemical reaction between suitable reducing agents and metal salt solutions.Metal sol SERS substrates are widely used because of their simple preparation process and good SERS enhancement effect.However,the biggest disadvantage of this type of metal sol substrate is that it is greatly affected by factors such as temperature and humidity,which will lead to different shapes and sizes of the prepared nanoparticles,and the nanoparticles are unstable and easy to agglomerate.In actual detection,as the detection system becomes more and more complex,the higher requirements are placed on our SERS substrates.First,how to prepare noble metal nanoparticles with uniform shape and size and high sensitivity;second,how to prepare nanoparticles with good stability and easy storage;third,how to prepare SERS substrate in a complex system,the molecules to be tested are specifically identified and captured at hot spots.MOFs are hybrid materials with a crystal structure composed of metal ion clusters and organic ligands through coordination bonds.Due to their excellent properties,MOFs have stimulated the interest of researchers.MOFs are one of the most attractive materials for developing sensors,more and more MOF-based SERS substrates have been fabricated.MOF-based SERS substrates have many obvious advantages:（1）Easy and tight immobilization of gold or silver nanoparticles（NPs）by porous surface of MOF,which is beneficial to improvement of stability of SERS substrate.（2）the rationally designed specific metal ion for MOF offering the interaction sites to capture the target sample molecules.（3）Organic ligand of MOF as an internal standard signal to improve the accuracy.In this paper,the advantages of MOF and SERS are fully exploited by combining MOF and traditional SERS substrates.In this study,three different metal-organic framework-based SERS substrates were prepared.The substrates were characterized by SEM,TEM,XRD and other instruments,finally,they were successfully used for the detection and analysis of biomarkers in serum.The specific research content and results are as follows:1.The Ag/Au/MIL-101 substrates were prepared by a three-step method for the specific detection of dopamine.The sensitivity of the detection is greatly improved by the azo derivatization reaction;the binding of p-mercaptoaniline（PATP）and dopamine（DA）increases the scattering cross-sectional area;and the selectivity of the detection is improved based on the specific reaction between DA and PATP.In addition,the MOF-loaded gold-silver nanoparticles improved the stability and uniformity of the substrate.We tested the SERS performance of the substrate first.The Ag/Au/MIL-101 SERS substrate can detect rhodamine 6G（R6G）molecules with a minimum detection concentration of 10^–8mol/L,which shows high sensitivity.Stability was investigated also.After 60 days of storage,the SERS signal remained basically unchanged,reflecting the high stability of the Ag/Au/MIL-101 SERS substrate.As a practical application,the proposed SERS method can be used to directly measure serum dopamine.In conclusion,The Ag/Au/MIL-101 SERS substrate has the advantages of high sensitivity,good uniformity,and simple preparation.and has important development potential in the rapid detection and application of disease biomarkers.2.When the size of gold nanoparticles was around 50 nm,the SERS enhancement effect was the best.We synthesized L-Au NPs/MOF-199 SERS substrate by the seed growth method and characterized it by SEM and TEM,which confirmed the successful preparation of L-Au NPs/MOF-199 SERS substrate.The substrate shows high sensitivity and 10^-9mol/L 4-MPy could be detected.As practical application,L-Au NPs/MOF-199-based Raman spectroscopy was used to detect5-hydroxyindoleacetic acid（5-HIAA）in serum,and the lowest detectable concentration was 4.67×10^-11mol/L.3.In order to further exert the interaction between the SERS substrate and the analyte,we realized the specific detection of low-concentration bilirubin in serum by adding graphene oxide（GO）in the process of synthesizing the material.Because the graphene oxide sheets and edge parts contain some oxygen-containing groups,there is a possibility of recombination between graphene oxide and metal-organic framework,and the electrostatic adsorption andπ-πinteraction between GO and BR can make bile red.The substrates of MOF/GO/Au were synthesized,and the SERS substrates were characterized by SEM,mapping,and other means,which confirmed the successful preparation of MOF/GO/Au substrates.4-MPy was selected as the probe.The sensitivity,stability,and uniformity of the SERS substrate were investigated by needle molecules,and the results showed that the SERS substrate had high sensitivity,good stability,and uniformity.The lowest concentration of BR that can be detected using this SERS substrate is 3.5×10^-9mol/L,and there is a good linear relationship in the concentration range of 10^-4to 10^-8mol/L.