Research On Biosensing And Tumor-targeting Drug Delivery System Based On Nucleic Acid Aptamer

The current medical level has been greatly improved,but the occurrence of tumor diseases is still one of the problems that endanger people’s health.Despite the rapid development of cancer diagnosis and treatment methods,the overall situation has not been substantially improved.It is of great significance to explore new sensing detection methods to achieve highly sensitive detection of tumor disease-related biomolecules,and develop tumor-targeted drugs to realize high-efficiency treatment of tumor diseases.Nucleic acid molecules are natural biopolymers that have the functions of storing,encoding,transmitting and expressing genetic information.They have excellent characteristics such as biodegradability,low toxicity,and good biocompatibility.Nucleic acid sensors that use nucleic acid molecules as identification elements have important practical applications in the fields of basic biology,chemical sensing and detection,medical diagnosis,and new drugs development.Adenosine triphosphate(ATP)is an energy molecule in life system,and it plays an important role in almost all cell metabolism and biochemical reactions.For example,the synthesis and replication of DNA requires the participation of ATP molecules,and the signal transduction process of cells also needs the presence of ATP molecules.However,when ATP molecules in the body undergo abnormal metabolism,it often leads to diseases,such as common hypoglycemia diseases and cerebral ischemia diseases.Therefore,it is extremely important to develop high-sensitivity strategies for ATP molecules detection.In this thesis,we combined the split nucleic acid aptamer and the fluorescent dye thioflavin T(Th T)to construct a "turn-on" optical method for the highly sensitive detection of ATP.The split aptamer fragments can only form intramolecular G-quadruplex with less G-quartets.In this condition,few Th T molecules embedded in the G-quadruplex,and the fluorescence is very weak.In the presence of ATP molecules,intermolecular G-quadruplexes with more G-quartets can be formed,more Th T molecules embedded in the G-quadruplex,and the fluorescence is significantly enhanced.By detecting and analyzing the fluorescence signal of Th T in the system,the concentration of ATP molecules can be determined.This method has high sensitivity and good specificity.The sensing strategy is not only simple,fast,low cost,but also has high selectivity and practicality.Compared with ATP detection in buffer solution,it shows better detection performance in diluted serum,and the sensitivity is improved by two orders of magnitude.Nucleolin is a multifunctional RNA-binding protein that can be found in in the nucleonus of cells.Nucleolin is indispensable in the proliferation process of many cells.At the same time,the biosynthesis and maturation of ribosomes also require the regulation of nucleolin.In some actively proliferating cells,especially some cancer cells,the expression of nucleolin is abnormal,so it can be used as a biomarker for tumor detection.Nucleolin can also promote the secretion of angiogenin,which is a potential molecular target for cancer treatment.Herein,we constructed a tumor-targeted drug delivery system with p H responsiveness.The system is composed of nucleolin aptamer,C-rich sequence and G-rich sequence.The anticancer drug doxorubicin(DOX)was inserted into the GC base pair of double-stranded DNA to form a nucleic acid drug delivery system with dual responsiveness of p H and nucleolin.Due to the specific interaction between aptamer and nucleolin,the drug-loaded nucleic acid probe system can be internalized into tumor cells,and the drug DOX can be released in the acidic environment in tumor cells.The released DOX can effectively inhibit the growth of tumor cells.In addition,owing to the unique fluorescent properties of DOX,the processes of tumor-targeted delivery and release of drugs can be monitored through fluorescence changes.