The Functionalization And Biological Application Of DNA Nanostructures

DNA nanostructures have been widely applied in biosensing,biodetection,drug delivery carriers and assembling high-order nanomaterials.Because these nanostructures have the capacity of precisely base paring,excellent biocompatibilty and biostability,high cell membrane permeablity and controlled drug release property.Based on two kinds of DNA nanostructures,this paper researched the biological application and functionalization of DNA nanostructures.This work consists of two parts.1.The first part is the application of DNA nanostructures in smart drug delivery and drug delivery carriers,including chapters 2,3 and 4.In chapter 2,we constructed a smart drug delivery system based on six-helix nanostructures.The structure has several several important elements: 1.Intelligent “switch”,which can be identified and opened by specific molecules;2.Covelent linkage of a number of drug molecyles,with high efficiency and low toxicity.6-helix DNA nanostructures could enter cancer cells with high uptake efficiency;after that,key strands were added,then 6-helix could be divided into 3-helix hemi-bundles to expose internal drug binding sites;at last,drug maytasine（DM1）interferenced microtubule formation,resulting in cell apoptosis.Intelligent durg delivery system has realized the controlled drug release in targeted locations,which could significantly improve efficacy and reduce side effects of DM1.6-helix nanostructures could be used as transmembrane channels,drug delivery carriers and molecular capsules,for their hollow tubes and high mechanical stability.And the inner diameter and loose degree of 6-helix determine the size of the molecules to be delivered.In chapter 3,we combined the theory simulation and small angle X-ray scattering（SAXS）techniques to characterize ionic strength as well as small molecules loading effects on 6-helix structures.The results showed that with a higher ionic strength,the inner diameter of 6-helix would decreased;after ethylation of DNA skeleton to shield the negative charge of phosphate groups,the inner diameter also decreased;at the same time,SAXS could reflect the size information of 6-helix in the physiological state.This research will help to control the morphology and mechanical properties of DNA nanostructures and provide theoretical basis on their biological application.Transfering gene into cell nucleus is an important part of gene therapy.High efficient and safe delivery carriers would improve the efficacy of gene therapy significantly.To achieve the above two purposes,in chapter 4,we constructed the composite structures of DNA tetrahedron and nucleus localization signal（NLS）to improve the uptake efficiency of DNA tetrahedron into cell nucleus.Covalent conjugation of DNA tetrahedron and NLS through “click chemistry” improved the stability of composite structures;extention alkaline NLS₁₂ to acid NLS29 significantly reduced the nonspecific binding of DNA tetrahedron and NLS and keeped the capability of targeting nuclei.This study pave a new way for the clinical gene therapy.2.The second one is the self-assembly of nanoparticles guided by DNA nanostructures,including chapter 5.In chapter 5,we used DNA tetrahedron to load gold nanoparticles and quantum dots,then adopted the idea of “brick and cement” to assemble homogeneous and heterogeneous nanoparticle cluters.This simple and universal method has realized DNA-nanoparticle conjugates of fixed valences,and DNA tetrahedral cages played important roles in keeping the stability of nanoparticles.More importantly,the construction of superstructures made new influence on the properties of the nanoparticles.This part provides a new way for constructing exquisite nano-platform.Through the above work,we constructed a new platform for smart drug delivery and drug delivery carriers based on DNA nanostructures,and assembled the superstructures of inorganic nanoparticles by a simple and universal way.These research have great significance in biological application and functionalization of DNA nanostructures.