Photo-Flourescent Characteristics Of Unlabeled Single Strand DNA

In the traditional research of nucleic acid,specific reagents,fluorescent agents or probes often need to be added into samples,which usually causes problems of complicated operation steps,high cost,sample pollution,environmental pollution and so on.To resolve this problem,based on the standard photoluminescence(PL)technique,we experimentally study the effects of several factors on the fluorescence characteristics of single strand DNA(ssDNA)samples.Combining with the structures of the ssDNA samples,the physical mechanism of these effects are analyzed.Furthermore,we also explore the identification of unlabeled ssDNA samples under different conditions.The main contents and results of this thesis are listed as follows:(1)The effects of concentration,volume,and number of single-stranded bases on the photoluminescence characteristics of single-base ssDNA samples(containing only one kind of A,C,T,and G)are investigated.It is demonstrated that the effect of volume on the fluorescence characteristics of samples can be neglected.The fluorescence intensity of the sample enhances nonlinearly with increasing concentration and number of single-stranded bases.In addition,when the excitation wavelength varies in the range of 270-490nm,the emission wavelength varies in the range of 350-600nm.It indicates that the energy-level structures of the four bases are similar.Due to the differences of variety and number of the chemical bonds,the four kinds of ssDNA samples present different relations of excitation wavelength-emission wavelength and excitation wavelength-emission peak intensity.(2)When the excitation wavelength varies in the range of 270-310nm,The photofluorescence characteristics of the ssDNA samples with different concentration or number of single-stranded bases are analyzed,It is found that the four samples could be effectively identified according to their spectral shapes,peak wavelengths and overall intensities.Interestingly,this identification method shows robustness of concentration and number of single-stranded bases.(3)Two different single-base ssDNA samples are mixed at different volume ratios.Then,the photoluminescence characteristics of these ssDNA mixture solution are examined.The experimental results indicate complex interactions between different kinds of ssDNA samples.To investigate these interactions,we introduce a phenomenological parameter named spectral interaction term M,which can describe inhibition or enhancement of the photoluminescence due to ssDNA interaction.(4)Combining the above experimental results with ssDNA structures and band characteristics,we can infer that the base structure contains a conjugated double bond,which induce the ?-?*electron transition.Changes in sample concentration,base sequence,and the polarity of the solvent may cause the conjugation of n-? electrons.Consequently,the photofluorescence characteristics of the samples are influenced.The results obtained in this thesis are of great significance for the study of photoelectric properties of ssDNA,and can provide a reference for the technology of nondestructive ssDNA detection.