Construction Of Multidimensional Highly Sensitive SERS Substrate For Biochemical Sensing

Surface-enhanced Raman spectroscopy(SERS)is a robust technique with a unique fingerprint effect,simple and fast preparation,and nondestructive data acquisition in an aqueous environment,which has led to applications in several different directions,including chemicals,biomedicine,physics,and so on.Whereas in practical application,SERS technology has several downsides related to low detection performance,poor universality,and high cost.The excellent detection performance is the key to SERS analysis and is closely related to the high sensitivity of the SERS substrate.Usually,there are two effective strategies to raise the sensitivity of SERS substrates:one is to develop plasmonic nanostructures with abundant "hot spots" to enhance the SERS activity of the substrate;the other is to increase the contact with the surface of the SERS substrate by improving the special affinity of target analytes.In this thesis,we fabricated different SERS substrates including rigid/flexible twodimensional(2D)planar substrates and flexible three-dimensional(3D)substrates,and studied the effects of support material,spatial structure,size,and concentration of noble metal nanostructures on SERS activity.Furtherly,we verified the increased sensitivity of SERS substrates by functional modification and investigated the practicability of these substrates.The main works of this thesis are as follows:1.Research on rigid 2D SERS substrates.The high-density Au and Ag nanoparticles(NPs)were immobilized on glass slides by a simple and low-cost selfassembly strategy as rigid 2D SERS substrates(Glass/AuNPs and Glass/AgNPs).The effect of the material,size,and density of nanoparticles on the SERS activity was studied.4-Mercaptobenzoic acid(4-MBA)was used as a probe molecule to verify the sensitivity,uniformity,and reproducibility of the two substrates.The glioma and normal brain tissue samples were sensitively analyzed and identified by Glass/AuNPs combined with the principal component analysis(PCA)method.Escherichia coli(E.coli),Staphylococcus aureus(S.aureus),and Sporothrix schenckii(S.schenckii)were distinguished by Glass/AgNPs combined with the PCA method.2.Research on flexible 2D SERS substrates.To further improve the flexibility and the density of "hot spots" on the surface of 2D SERS substrates,and increase the interaction between analytes and "hot spots",the flexible 2D SERS substrates(PVDF/AuNPs)were fabricated on the polyvinylidene fluoride(PVDF)membranes by the electrostatic adsorption self-assembly of Au nanoparticles.The effect of the size and concentration of nanoparticles on the SERS activity was studied.4-MB A was adopted as a probe molecule to verify that the substrate featured high sensitivity,uniformity,and repeatability.PVDF/AuNPs substrate was integrated with a portable Raman spectrometer for liquid and gas environmental detection,realizing real-time quantitative monitoring of pH,and high-sensitivity detection of benzene gas and cigarette smoke.3.Research on flexible 3D SERS substrates.The number and density of "hot spots"on 2D flexible SERS substrates were limited by the spatial structure.To further improve the detection sensitivity of flexible substrates,nanoparticles were assembled on the 3D ZnO nanorods to produce high-density SERS "hot spots",and the SERS substrate was chemically modified to improve the capture efficiency of the analytes.Tussocky ZnO nanorod arrays were grown on flexible porous PVDF membranes by hydrothermal method,combined with an in situ chemical growth of AuNPs on Au film-coated ZnO nanorods,a 3D-rosettelike BigAuNP/Au/ZnO/P nanostructure with abundant "hot spots"was fabricated.The effects of Au film thickness and chemical growth of AuNPs on SERS activity were studied.4-MBA was used as a probe molecule to verify the sensitivity,uniformity,and repeatability of BigAuNP/Au/ZnO/P.With the 4-MBA molecular monolayer as the sensing interface,a highly sensitive and quantitative detection method for gaseous/liquid putrescine and cadaverine was constructed,and the detection performance of the 3D flexible SERS substrate was verified by using real pork samples.In conclusion,the high-density noble metal nanoparticle assembly on the surface of solid substrates is conducive to the excitation of surface plasmon resonance and coupling effect for significant enhancement of the SERS activity.Compared with rigid support materials,the rough surface and microporous structure of flexible membranes increase the nanoparticle attachment and generation of "hot spots".3D semiconductor nanostructures with much higher spatial dominance allow the assembly of nanoparticles in multiple orientations for the formation of "hot spots",which significantly enhances SERS activity through the localized surface plasmonic resonance effect and chargetransfer effect.In addition,surface modifications of SERS substrates enable selective adsorption and enrichment of the analytes with weak affinity to the substrate and small Raman scattering cross-section,effectively improving the detection sensitivity for further promoting the practical application of SERS technology in the field of biochemical sensing.