Biosensors Based On New DNA Probes And Nanomaterials For Sensitive Detection Of Nucleic Acids

It is very important and urgently needed to develop rapid, sensitive, and high cost-effective biosensors in the field of molecular diagnostics, drug discovery, and food safety. Advances in nano science and DNA technologies have provided powerful tools for researchers to design biosensors with high sensitivity in detecting pathogenic substances. This thesis includes the following three parts, describing our efforts to realize fast, sensitive and selective detection of target DNA molecules:First, I studied the interactions between graphene oxide and iridium(Ⅲ) complex. Graphene oxide(GO) has been widely used in the field of biomolecular detection due to its unique physical structure and physiochemical properties. Iridium complexes have exhibit advantageous photonic properties for bioimaging and biosensing. In this work, iridium(Ⅲ) complex with carboxyl group was synthesized and activated with N-hydroxysuccinimide. By studying the interaction between GO and iridium(Ⅲ) complex, we found that the interaction of GO/Ir complex was different from GO/FAM dye molecules, in which electrostatic attraction might play a predominant role.The result also suggested that Ir complex as a luminescence probe could be effectively quenched by GO nanosheets via F?rster resonance energy transfer(FRET).Second, The N-hydroxysuccinimideactivated Ir complex was tagged to the amino terminate of single-stranded DNA(ss DNA) in my work. The Ir-ss DNA probe was further combined with graphene oxide(GO) nanosheets to develop a GO-based biosensor for target ss DNA detection. This GO-Ir-ss DNA biosensor could realize fast, sensitive and selective detection of target DNA. We also compared thephotostability Ir Complex, FAM and their GO-based biosensors. The results indicated that the GO-Ir-ss DNA biosensor possesses better photostability than GO-FAM-ss DNA biosensor.Third, I designed a “signal-on” strategy using Surface-Enhanced Raman Scattering(SERS) and developed an ultrasensitive detection for the DNA sequence of Mn SOD. In this design, the probe DNA molecules were hybridized with the target DNA, then selectively digested by the enzyme of Exo Ⅲ. It led to the generation of residual DNA labeled with Cy5, and dissociation of the intact target DNA from the residual DNA sequence. The target DNA could be repeatedly hybridized to other probe DNA molecules and then digested by Exo Ⅲ, which was the foundation of recycled use of the target DNA for amplified signals. The SERS substrates were integrated into this design to provide “signal-on” responses sensitive to the DNA changes. This design of SERS biosensor is featured with high sensitivity, excellent specificity and reproducibility for the detection of the target DNA sequences.In summary, the GO-Ir-ss DNA and SERS biosensors have been successfully designed, suggesting a performance of sensitive and selective detection of target DNA molecules. Our methods may offer a new way to detect the target DNA sequences as important biomarkers, promising good applications in disease diagnosis or in the field of biomedical research.