SERS Detection Of DNA Bases Adsorbed On Silver/Silicon Nanoporous Pillar Array

DNA is the carrier of genetic information of organisms, and the four DNA bases, namely adenine (A), guanine (G), cytosine (C) and thymine (T), are the basic components of DNA and play important roles in genetic expression and replication. All kinds of modern technology was used to explore the life processes about DNA from molecular level. Because most of the base molecules are difficult to prepare in large amounts and usually have very low solubility, it is hardly to be investigated by normal Raman spectroscopy (NRS) because of its small scattering cross section. The discovery of the surface-enhanced Raman scattering (SERS) technique opened a new field for the low-concentration detection of biological molecules. For the ultra high sensitivity of SERS detection, low concentration solution of the DNA bases and even single molecule detection can be achieved. In this paper a regularly patterned silver (Ag) structure was prepared by an immersion plating method on a template of silicon nanoporous pillar array (Si-NPA). Using Ag/Si-NPA as active substrates, the adsorption behavior of three DNA bases, guanine, cytosine, and thymine at low concentration was studied by surface-enhanced Raman scattering (SERS) technique. The main results achieved in this thesis are listed as follows.1. Using Ag/Si-NPA as SERS-active substrates, the three DNA bases guanine, cytosine and thymine at different concentration were detected. The result show that the limit detections of the three bases were10-7mol/L,10-9mol/L,10’8mol/L respectively, which were close to the lowest concentration reported in the literature. This indicated that Ag/Si-NPA is an effective SERS active substrate for all the DNA bases.2. Based on the obtained SERS spectra and the comparison with NRS, it was deduced that the three DNA bases were all adsorbed on the surface of the silver particles slightly tilted but with different inclination angles. The plane of thymine has smaller inclination angle than guanine and cytosine. The adsorption sites for different bases were similar-all through carbonyl group (C=O) and nitrogen atom (N). With the reducing of concentration, the plane of the base molecules were all tend to be parallel to the surface of substrate.3. The SERS spectra of adenine (A) and thymine (T) co-adsorbed on Ag/Si-NPA were detected. It was found that when the two kinds of bases solution were mixed with the same concentration, the intensity of Raman signal was much weaker compared with separately detection and the Raman signal of thymine almost disappeared. This phenomenon indicated that the hydrogen bond between adenine and thymine was stronger than the bond between molecules and substrate, and the A-T base-pairs adsorbed to the substrate via adenine. When the concentration ratio between thymine and adenine was100:1, the SERS signal of both bases appeared, which can realize the hybrid detection of the two bases.The results indicate that Ag/Si-NPA active substrate has ultra high sensitivity in the field of biological detection, and it is expected to become ideal active substrate which can be widely used for SERS technology.