Research On Detection Of Biomolecules And Tumor Targeted Diagnosis And Treatment Based On DNA Self-assembly Technology

Due to the intrinsic properties including the highly predictable and specific intermolecular interactions between the Watson-Crick base pairing and the programmability of the sequence,DNA has become a kind of vital biological functional materials.Invented by Seeman in the early 1980 s,DNA self-assembly techniques have grown fast in the past decades.Based on DNA self-assembly strategies,this thesis has constructed a biosensing platform which has successfully applied for the detection of target DNA and lysozyme,extracellular pH imaging,targeted therapy system and molecular logic operations.Those DNA self-assembly techniques provide a new perspective and strategy for developing efficient biocomputational systems and has great significance in the fields of DNA nanostructures,disease diagnostics and drug delivery systems.This thesis carried out the following three aspects of work: 1.A versatile homogeneous chemiluminescence biosensing platform based on exonuclease-assisted hybridization chain reaction.This work proposes a strategy for self-assembly of DNA polymer wires consisting of numerous G-quadruplex units via the execution of hybridization chain reaction between initiator with three kinds of DNA hairpins and target cycling mediated by Exo III.The DNA nanowires are applied as a signal amplifier to construct a universal chemiluminescence biosensing platform,which achieves ultralow detection limit with LODs of 5.7 fM for target DNA and 4.2 fM for lysozyme,excellent specificity to distinguish mismatched initiator even one-base mutation and interferent proteins,and good performance in real sample analysis.2.DNA logic assembly powered by a triplex-helix molecular switch for extracellular pH imaging.This work proposes a pH-programmable strategy to self-assemble DNA nanostructures through triplex-helix molecular switch triggered by pH changes.The successful operation of the mechanism is well regulated by an upstream pH-dependent substrate based on the reverse Hoogsteen-motif in triplex DNA.Through using pH and initiator/H0 complex as the environmental stimulus,two sets of logic gates(“AND” gate under weak acidic/neutral/basic pH and “INHIBIT” gate under strong acidic pH)are successfully constructed which constitute the specific combinational circuits.In addition,this strategy is successfully applied to extracellular pH imaging.3.A self-assembly core-shell nucleic acid nanostructure for targeted therapy of Karpas299 cancer cells.This work successfully constructs a core-shell nucleic acid nanostructure in a layer-by-layer assembly way.The Y-scaffold nucleic acid monomer is linked by disulfide bond to obtain the spherical nucleic acid core which has higher negative charge density.The spherical core can be combined with the positively charged cationic polymer LPEI,and further be coated with the DNA shell.The Y-scaffold nucleic acid monomer of the spherical core contains ALK siRNA for specific oncogene silencing.The DNA shell is loaded with the therapeutic drug doxorubicin,and the CD30 aptamer is designed outside the DNA shell which would specifically recognize and bind Karpas299 cells.Under acidic conditions,the DNA shell forms triplex structure which would induce intracellular release of its drug payload.At the same time,the siRNA in the core is exposed.It is expected to achieve combined cell-targeted chemotherapy and gene therapy for tumor.