| Surface Enhanced Raman Spectroscopy（SERS）,a Raman spectroscopy derivative assisted by nanomaterials,has been widely used in the fields of food safety,environmental monitoring,and material synthesis because of its ultra-high sensitivity and nondestructive fingerprint spectral resolution,and is rapidly growing as one of the most sensitive techniques for in situ spectroscopic detection of surface chemistry.In addition,SERS can be used for screening and staging diagnosis of clinical tumor and disease samples through the detection of relevant biomarkers.However,SERS detection of biomarkers is hampered by two factors.Firstly,it is difficult to obtain molecular fingerprint information from complex vibration spectrum due to the non-specific interaction with co-existing substances in biological matrix.Secondly,the content of biomarkers in vivo is low,and some small molecular markers have low Raman activity,which requires higher sensitivity for prediagnosis and prognostic treatment of tumors and diseases.Therefore,the clinical transformation of SERS method is still a challenge,and the current SERS strategy needs further development and standardization in the diagnosis of oncology and other diseases.SERS detection methods are broadly divided into two categories including direct detection of SERS signal of target objects and indirect detection by using Raman tags that can have specific interaction with analytes.Direct SERS assays obtain"finger print"information of target molecules without further labeling,providing validated information from biomarkers,cells,and thus offering the possibility to unravel target components and disease mechanisms.However,due to the complexity of biological samples,SERS cannot directly detect countless biomarkers.Compared with the direct detection method,the signal of Raman label molecules is simple and strong,which has significant advantages in detecting complex environments and improving sensitivity.Aggregation of SERS active nanoparticles leads to low reproducibility.The key to achieving high sensitivity and reproducibility is the selection and tuning of the composition of the SERS substrate.In this thesis,the stability of nanoparticles and the homogeneity of the system were improved greatly by prepared nanoparticles with core-shell structure and self-assembled two-dimensional substrates,and the detection and analysis of tumor and neurodegenerative disease markers were achieved using direct detection and indirect detection using Raman signal molecules of SERS strategies,respectively.The following three main works were carried out.Inositol hexaphosphonate-coated silver nanoparticles（AgNPs@IP6）were simply synthesized in a very short time using inositol hexaphosphate（IP6）as a protective shell layer.It overcomes the problems that AgNPs with strong LSPR are easy to be oxidized,have poor stability and easily aggregate.By micellar connection,a large number of hot spots are formed by self-assembly between particles,which enhance the detection sensitivity.AgNPs@IP6 was used to detect5-hydroxytryptamine（5-HT）,a marker of pheochromocytoma,and the level of 5-HT in vivo has become one of the indicators for screening neurodegenerative diseases in clinic.The linear quantification range of 5-HT detection using this substrate was from10-4 mol/L to 10-7 mol/L,and the LOD could reach 4.53×10-8 mol/L,which was much lower than the 5-HT level in healthy individuals,while the 5-HT level in patients with major depressive disorder was 0.3±0.19μmol/L,which was higher than the LOD of the method and within the linear range,indicating that the SERS substrate based on AgNPs@IP6 is expected to be applied to the early diagnosis and prognosis of the disease.However,complex biological matrix will interfere with the detection of 5-HT in practice.Further exploration of methods to improve the specificity and selectivity of the assay is needed next.In Chapter 2,core-shell nanoparticles were synthesized to achieve the direct detection of 5-HT.However,in the presence of interference from other body fluid components,effective information could not be extracted sometimes according to the analysis of the spectral fingerprint obtained by direct detection of the target object.Therefore,the Raman signaling molecule 4-mercaptophenylboric acid（4-MPBA）was modified on the surface of AgNPs@IP6.The sialic acid（SA）was assembled on the substrate by esterification of 4-MPBA with SA to form SERS labels for selective detection of 5-HT.Through the specific adsorption of SA and 5-HT,the affinity between the target molecule 5-HT and SA triggers the aggregation of SERS tags,generating more"hot spots"and enhancing the Raman signal of 4-MPBA.The concentration of 5-HT showed a good linear relationship with the change of SERS label signal intensity in the range of 10-4 mol/L～10-8 mol/L,with LOD of 2.51×10-9 mol/L and correlation coefficient of 0.9717.This method has good selectivity and high sensitivity for the detection of 5-HT in serum,as well as strong anti-interference ability,and is expected to achieve application from laboratory to clinical medicine.In Chapter 4,two-dimensional SERS sensors were prepared by layer self-assembly method,and vanillin mandelic acid（VMA）in urine was selectively detected by redox reaction of K3[Fe（CN）6]（potassium ferricyanide）.K3[Fe（CN）6],as a SERS signal molecule,contains cyanogroup（-CN）with a unique and strong Raman signal in the Raman silent zone,which can selectively oxidize VMA into vanillin in acidic environment.K3[Fe（CN）6]is far away from the"hot spot"area on the surface of ITO/Au,and the signal decreases.According to the decrease of K3[Fe（CN）6]Raman signal after the reaction between sensor and analyte,the VMA has a good linear relationship in 5×10-2～5×10-8mol/L,the correlation coefficient is 0.9811,and the LOD of VMA is 4.2×10-9mol/L.It indicates that the SERS sensor established in this work has the potential to be a clinical diagnostic tool for pheochromocytoma. |
PDF Full Text Request