The Investigation Of Interfacial Hybridization And Functional Nanostructured Biointerface

Recently, the research interests in the biosensors and biochips are focused on the fabrication of functional nanostructured biointerfaces and model of DNA interfacial hybridization, and the fundamental understanding of the interfacial bioelectrochemical processes within these systems. Thermodynamics and kinetics of the interface reaction may substantially differ compared to the same reaction in bulk solution as a result of the species-interface interaction, interfacial concentration gradients and steric hindrance in the investigation of gene biosensors. So it is very important to investigate the DNA hybridization on solid-liquid interface for the design of gene biosensors and nanostructured biointerfaces. At the same time, Semiconductor nanomaterials typically have the unique optical, electronic, magnetic, and catalytic properties. Thus, the architecture of functional nanostructures biointerfaces, which are fabricated by semiconductor nanomaterials and biomolecules, has potential applications for biological application and medical diagnosis. The research of interaction between semiconductor nanomaterials and biomolecules is propitious to fabricate various functional nanostructured biointerfaces with simple, highly selectivity and sensitivity. The biochemical functional effects of nanostructured materials on biomolecules, namely the security of biomolecules themselves, are studied.Accordingly, the emphasis of this thesis is placed on investigating the interfacial DNA hybridization and functional nanostructured biointerface. These works can be divided into two parts: (1) the hybridization of oligonucleotides probe with matched or mismatched DNA target was monitored by a combination of electrochemical control and in situ quartz crystal microbalance technique. The influence of different interfacial electricfield on the efficiency of hybridization was investigated. The effect of the orientation of oligonucleotides probe and micro forces on DNA hybridization under interface electric field was discussed; (2) The DNA-template method was used to prepare CdS QDs (Quantum dots)-CT DNA (calf thymus DNA) nanostructured bioconjugates, and their photoluminescent (PL) properties were investigated. The main results are summarized as follows:1. The influence of different interfacial electricfield on the efficiency of hybridization investigated by electrochemical quartz crystal microbalance (EQCM) technique(1) Under the condition of controlling a suitable positive potential, target DNA will be enriched around the working electrode, which improves the rate of hybridization of oligonucleotides probe with target DNA. It's found that at this condition the orientation of probe DNA adsorbed on the electrode surface is parallel, and the orientation leads to the maximum nonspecific adsorption between probe DNA and electrode surface. Thus, the specificity of DNA hybridization is weakened, which leads to "false positives".(2) The orientation of probe DNA adsorbed on the electrode surface is perpendicular by means of an appropriate negative potential. This orientation leads to the minimum nonspecific adsorption between probe DNA and electrode surface, which is propitious to keep the specificity of DNA hybridization and can availably halt hybridization for mismatched target DNA.(3) Because it does not need to modify the electrode surface by alkanethiols, the surface coverage of probe DNA is as high as 2.2×10¹³ molecules·cm^-2, which predigests the process of preparation and enhances the sensitivity of detection.2. Investigation of PL properties of CdS QDs-CT DNA nanostructured biointerface(1) Utilizing the electrostatic attraction, CdS QDs-DNA nanostructured biointerfaces were prepared by using dsDNA or ssDNA as a template of CdS QDs. In addition, DNA, onto which CdS QDs were attached, acted as a protecting agent.(2) The UV-vis absorption spectra show that a similar on-set wavelength of CdS QDs protected by sodium pyrophosphate, dsDNA or ssDNA. The absorption onset of these CdS QDs blueshift about 45 nm compared with that of the bulk CdS, which indicates a quantum size effect. In addition, the size and production of CdS QDs were almost not affected by different dsDNA or ssDNA concentration within the range of 200 mg·L^-1 to 300 mg·L^-1 . In the IR spectra, the characteristic peaks of DNA from the nanostructured biointerfaces of CdS QDs-dsDNA or CdS QDs-ssDNA almost don't show any shift compared with those from CT DNA. Thus, it is likely that CdS QDs haven't maked any damage on DNA. The photocurrent spectra indicate that a remarkable photocurrent signal of CdS QDs capped with sodium pyrophosphate was observed. But the photocurrent signal of CdS QDs protected by DNA was hardly observed, due to many surface defect states.(3) The analysis on PL spectra shows that:(A) The PL enhancement effect of DNA on CdS QDs is expressed as follows:I_CdS-Na4P2O7 CdS-dsDNACdS-ssDNA.(B) The PL intensity of CdS QDs- DNA enhances while increasing the DNA concentration within the range of 200mg·L^-1 to 300 mg·L^-1.(C) The factors of the PL enhancement effect of DNA on CdS QDs are:(a) The phosphate backbone of DNA has a certain rigidity. The rate of collisions between CdS QDs on the phosphate backbone with negative charge is far less than that in unrestricted space, which leads to more ordered array of CdS QDs. These two factors enhance the PL quantum yield. The distance between the CdS QDs adsorbed on dsDNA is shorter than that on ssDNA. Thus, the CdS QDs adsorbed on dsDNA are easier to collide, which leads to a weaker intensity of PL.(b) The PL spectral band of CdS QDs observed is due to surface defect states. The intensity sequence of surface defect states of CdS QDs from photocurrent spectra is: CdS-Na₄P₂O₇