Novel Biosensing Methods Based On Polydopamine Nanomaterials And Nucleic Acid

Polydopamine nanomaterial is a biopolymerized material with excellent advantages such as simple synthesis,low cost,good biocompatibility and biodegradability and has been broadly applied to biological analysis,biosensing and imaging.DNA probes have strong specificity.Meanwhile,they can be easily modified with fluorophores and used for intracellular detection.In this thesis,three novel fluorescent biosensors were constructed based on polydopamine nanomaterial and FAM labeled single-stranded DNA（ssDNA）to detect the concentration of exonuclease I（Exo I）and melamine.（1）In chapter 2,a novel fluorescence sensing platform based on polydopamine nanospheres and FAM labeled ssDNA has been developed for monitoring the concentration of Exo I.The ssDNA can be adsorbed on the surface of the nanospheres through a good non-covalent interaction with the polydopamine nanospheres.The fluorescence of the FAM was subsequently quenched by the polydopamine nanospheres via energy transfer or electron transfer.In the presence of Exo I,the FAM labeled ssDNA was specifically degraded by Exo I,producing mono-or oligonucleotide fragments,which were not able to be adsorbed by the polydopamine nanospheres,and thus the fluorescence signal was retained.The retained fluorescence of the sensing platform was found to be linear with the concentration of Exo I in the range of 0.15 to 10 U mL^-1（R²=0.998）with a detection limit of 0.05 U mL^-1.In addition,the sensing platform was highly selective toward Exo I and the process was simple,and low-cost.（2）In chapter 3,We designed a FAM-ssDNA/PDANS nanocomplex based on polydopamine nanospheres and FAM labeled DNA probe to detect the concentration of melamine.In the absence of melamine,the FAM labeled DNA probe could be adsorbedonthesurfaceofpolydopaminenanospheres,forminga FAM-ssDNA/PDANS nanocomplex.Due to energy resonance transfer or charge transfer,the fluorescence of FAM could be effectively quenched by polydopamine nanospheres.At this time,the fluorescence of the nanocomposite was in the“off”state.In the presence of melamine which could form hydrogen bonds with thymine（T-base）,the configuration of ssDNA would be induced to transform into double-stranded DNA（dsDNA）.Owning to the weak interaction between dsDNA and polydopamine nanospheres,the structure of the nanocomposite was destroyed and the fluorescence of the system was in the"on"state again.We could detect the concentration of melamine by studying the fluorescence signal.The retained fluorescence of the sensing platform was found to be linear with the concentration of melamine and the detection range of our method was 0-800 nM（R²=0.989）.According to the 3σprinciple,the detection limit was 16 nM.The propsed method is a promising platform for rapid detection for melamine with merits of simplicity.（3）In chapter 4,we have synthesized polydopamine nanotube with strong fluorescence quenching ability and used FAM labeled ssDNA together,constructing a novel fluorescence sensing platform to detect the concentration of Exo I.Due to the interaction between the ssDNA and the polydopamine nanotubes,the ssDNA may be adsorbed on the surface or the inner parts of polydopamine nanotubes.The fluorescence of the FAM was subsequently quenched by the polydopamine nanotubes via energy transfer or electron transfer.In the presence of Exo I,the FAM labeled ssDNA was specifically degraded by Exo I,producing mono-or oligonucleotide fragments,which were not adsorbed by the polydopamine nanotubes,and thus the fluorescence signal was retained.The retained fluorescence of the sensing platform was linearly proportional to the concentration of Exo I in the range of 0 to 15 U mL^-1with a detection limit of 0.33 U mL^-1（R²=0.981）.In addition,the sensing platform was highly selective toward Exo I.Compared with the method based on polydopamine nanospheres in Chapter 2,the detection sensitivity was lower due to the different structures and quenching ability between nanospheres and nanotubes.But polydopamine nanotube show great potential in drug delivery and release due to its one dimensional and tubular structure,which is worthy of further study in the future.