Surface Enhanced Infrared Absorption Spectroscopy And Its Applications

Attenuated total reflection-surface enhanced infrared absorption spectroscopy(ATR-SEIRAS)is a sensitive and label-free surface/interface analysis technique.As an extension of the conventional infrared spectroscopy,SEIRAS can significantly improve the detection sensitivity and effectively reduce the signal interference from the bulk solvent water and environmental variations.Owing to its high surface sensitivity,this technique allows in situ and quantitative acquiring of spectroscopic information on the details of interfacial biological and chemical reactions.From the perspective of methodology,this doctoral thesis begins with the investigation of optical near-field effect in ATR-SEIRAS,and this effect is applied to improve the detection sensitivity of immunoreaction.Then,this technique is successfully applied in qualitative analysis of biological species and molecular interactions of DNA-DNA,DNA-protein,oligopeptides-protein and protein-protein.Besides,we develop the enhancement substrates of SEIRAS which broaden the spectral range of IR and significantly improve the enhancement factor.The following researches have been carried out:1.Study of the optical near-field effect of attenuated total reflection-surface enhanced infrared absorption spectroscopyWe demonstrated the distance-dependent signal intensity in ATR-SEIRAS by controlling the distance of target molecule away from the enhancement substrate.The target proteins were assembled on a gold nanostructured film with increasing distance controlled by direct adsorption,the specific interactions of aptamer-antigen and antibody-antigen.The characteristic signals of the target proteins drop quasi-exponentially with increasing the distance,i.e.,the enhanced IR signal in the case of aptamer-antigen is one order of magnitude higher than antibody-antigen due to the optical near-field effect and the smaller size of aptamer compared with antibody.Based on this strategy,a detection limit of 0.6 nM target protein is achieved and the kinetics and thermodynamics of protein-aptamer/antibody recognition process are further obtained from the time-and concentration-dependent IR signals fitted with a simplified two-compartment model.2.Insight into the electroless deposition of gold nanoparticle on ZnSeAu nanoparticles film was electrolessly deposited on the surface of ZnSe hemispherial prism and served as the enhancement substrate of SEIRAS,which brought the lower cut-off wavenumber of SEIRAS down to 650 cm-1.The systematic characterization of the reaction between HAuCl4and ZnSe is carried out using XPS,XRD,ICP-AES,AFM,TEM and electrochemical techniques,and the reaction mechanism is proposed afterwards.The kinetics of the reaction is further studied and its activation energy is measured to be 27.6 kJ/mol.The morphology and the structure of Au nanoparticles are well tuned by adjusting the reaction time,the temperature,the concentration of HAuCl4and adding additives.Finally,the localized surface plasmon resonance(LSPR)property of the Au nanoparticles is investigated,and we find the LSPR absorption of all the gold materials is located at Vis-NIR region.However,the enhancement factor of Au/ZnSe is about three times higher than the one for widely used Au/Si.3.Bioanalysis based on surface enhanced infrared absorption spectroscopy using Au/ZnSe as the enhancement substrateAu/ZnSe was applied as the enhancement substrate to broaden the spectral range and detection sensitivity of SEIRAS.The phosphorylation process of peptides and the DNA hybridyzation were in situ and label-free detected by surface enhanced infrared absorption spectroscopy.Quantitative analysis of protein kinase A(PKA)is made by the absorption intensity of the phosphate group.We find that PKA first bounded to peptide in the phosphorylation process,then it transfers the phosphate group from ATP to the peptide after bounding to ATP.The DNA hybridyzation process can also be quantified by phosphate group of DNA and we try to distinguish single nucleotide polymorphism of DNA from the different IR features of bases.Unfortunately,the sensitivity of SEIRAS is not enough.At last,the influence of self-assembled monolayer with different alkyl chain length on the immunoreaction kinetics was studied.4.Investigation of the structure of hydrated ions and the application of water absorption to the quantitative analysis in SEIRASThe structure of hydrated ions has been studied with attenuated total reflection infrared differential spectroscopy.It is found that the characteristic absorption of hydrated water redshifts with the increase of surface charge density of the cations/anions.The IR differential spectrum of hydrated magnesium ion is quite different from the other hydrated ions,which can be attributed to its unique coordination structure.The absorption of water molecules,which has a high IR cross-section,is further used for quantitative analysis.The intensity changes of H2O are proportional to the added target molecules and this strategy is developed as a universal method for quantitative bioanalysis using ATR-SEIRAS.5.Investigation of the localized surface plasmon resonance property of gold nanorod and construction of highly effective enhancement substrate for SEIRAS using gold nanorod assembliesGold nanorods with different aspect ratios were prepared with seed growth method and used as highly effective enhancement substrate for SEIRAS.Short gold nanorod,whose longitude LSPR is located in the Vis-NIR region,shows little enhancement to the IR signal of surface molecules,indicating that SEIRAS could only be achieved when the LSPR absorption of nanomaterials matches with the molecular absorption.Gold nanorods with high aspect ratios were synthesized by modified three-step growth method,and the LSPR absorption of its assemblies on ZnSe is tuned to middle-IR region.The enhancement factor for octadecanethiol self-assembly monolayer on the surface of gold nanorod is calculated to be 8×104,showing significant enhancement to IR signals.6.Preparation of vertically aligned Si nanowire array as the enhancement substrate for SEIRASVertically aligned Si nanowire array was prepared with nanosphere lithograph method.The diameter and length of Si nanowires can be effectively controlled by changing the time for reactive ion etching and chemical etching,which tunes the LSPR property of Si nanowires in the NIR-MIR range.It is found that the absorption intensity of Si nanowires drops with the decrease of incidence angle in the reflection mode and no absorption is detected when the incidence angle becomes 0°,indicating that the observed absorption is related to the longitude LSPR of Si nanowires.Compared with noble metal nanomaterials,Si nanowires show moderate infrared enhancement effect with an apparent enhancement factor of 16.