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Multiple-angle-of-Incidence Polarization Infrared Reflection-Absorption Spectroscopy and Surface-Enhanced Raman Scattering Research on Self-Assembled Monolayers

Author: BoYaLi
Tutor: YuRuQin；HuanShuangYan
School: Hunan University
Course: Analytical Chemistry
Keywords: self-assembled monolayers SERS MAI-PIRRAS 6-Mercaptopurine 2-Mercaptopurine Malachite green L- histidine
CLC: O657.3
Type: Master's thesis
Year: 2008
Downloads: 174
Quote: 1
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Abstract


Over the past two decades, self-assembled monolayers （SAMs） have witnessed tremendous growth in theory and application. There are some techniques such as electrochemistry, microscopy, spectroscopy et al., which have been successfully used to analyze the mechanism and structure of SAMs. However, some of the aforementioned methods either require high vacuum or cannot give molecular information. Normal Raman spectroscopy and Fourier Transform Infrared Spectroscopy （FTIR） can provide molecular vibrational information, however, they are seldom used to study SAMs in two dimensions for lack of sensitivity.As the advent of Polarization Infrared Reflection-Absorption Spectroscopy （PIRRAS） and Surface-Enhanced Raman Scattering （SERS）, the resolution and sensitivity of instruments are increased quickly. Both of them can provide rich molecular vibration information of SAMs.They have been extensively and successfully employed in analysis for material surface. In this thesis, we pay attention to the smooth metal. Using the MAI-PIRRAS technique, we get the information of 6MP on smooth Ag. In addition, the SERS spectra of some moleculars closely related to life are investigated.（1） Multiple-angle-of-Incidence Polarization Infrared Reflection-Absorption Spectroscopy （MAI-PIRRAS） has been used to study the adsorption mode and structural properties of 6-Mercaptopurine （6MP） self-assembled monolayers on smooth silver surface. Assignments of the observed bands by DFT calculations show that 6MP adopt the S atom and the N7 or N1 atom anchoring the silver surface. The adsorption intensity of the SAMs is multiplied by cosθto obtain corrected spectra. The adsorption intensity attains to the maximum at 35-40 degrees other than near the grazing angle. The characteristics of the spectra suggest that the SAMs of 6MP are arranged orderly in a parallel fashion with a dihedral angle of 35-40 degrees between the ring plane and the silver surface.（2） SERS is a powerful technich to get the SAMs information. In this thesis, we extend the Raman mapping technique together with SERS method to examine the SAMs of 2-mercaptopurine （2MP） molecules adsorbed at the gold surface. Based on the results of B1LYP/ 6-31G calculation method, it is concluded that 2MP adsorbs on the gold electrode via S, N1 and N3 atoms in the acid medium and in the case of alkaline medium it adopts the adsorption modes with S and N1 atoms inclining to the gold surface. The desorption potential of 2MP monolayers formed at the gold surface from the acid solution occurred around -1.6V,while 2MP monolayers assembled at the surface from a basic media, was at -1.4V.（3） Through self-assembly technique, Nano Au of 50nm were adsorbed onto the polyvinylpyrrolidone modified glass surface to form SERS active substrate. The proposed substrate possessed the merits of easy preparation. Malachite green, a prohibited animal drug, was used as probe SERS active molecule. The relatively standard deviation of the SERS responses on the substrate was lower than 10%. The substrate retains good stability and high SERS activity after dipped in water for 48h. The intensity of the malachite green on the substrate is so high that 1000cps SERS signals can be observed from 1×10-8 mol·L-1 malachite green sample. The lowest detection limit for malachite green was 5×10-9 mol·L-1.（4） Amino acid is the basic unit of protein molecules, which has clease relathionship with life activity. L-histidine is a kind of necessary amino acid.The absorption process of L-histidine on the rough surface of Ag is analyzed with the SERS technique. The result shows that the L-histidine can achieve stable SAMs after 10.5h. The theoretical vibrational value of L-histidine is calculated by B1LYP/ 6-31G method. The result shows that the atom of N and O of L-histidine are close to the surface of silver.

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CLC: > Mathematical sciences and chemical > Chemistry > Analytical Chemistry > Instrument analysis ( physics and physical chemistry ) > Photochemical analysis ( spectral analysis method)
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