Fluorescent Ligand Binding Specificities Sensitized By Nucleic Acid Structure Modification And Sensing Applications

DNA oligonucleotides have become popular tools for developing sensing platforms due to their rich structure polymorphisms and their ability to specifically bind fluorescent ligands.The modification of the nucleic acid can change the original structure and help to strengthen the binding affinity with the fluorescent ligand.It is of great significance for the development of nucleic acid structure-based fluorescent probes and sensing applications.In this thesis,Hypericin?Hyp?and Nitidine chloride?NIT?were used as fluorescent ligands,and polarity-inverted G-quadruplex?G4?and ligand-induced parallel double-stranded DNA?ps-DNA?were used as the objects.Based on studies of interactions between fluorescent ligands and modified nucleic acid molecules,we have developed a DNA-based Ba²⁺sensor with high tolerance to K⁺,and then developed a DNA-based parallel supramolecular fluorescent nanoassembly.The main contents are as follows:1.Polarity inversion sensitized G-quadruplex Ba²⁺sensors with K⁺tolerance.Due to the high abundance of K⁺in environments and K⁺-induced high stability of G-quadruplex?G4?,developing a selective G4-based fluorescent sensor for other metal ions with K⁺tolerance is a great challenge.Herein,we found that even in the presence of 15000-fold excess of K⁺,Ba²⁺exhibits a highly specific binding with a human telomeric G4?htG4?in comparison with other G4-binding metal ions such as Pb²⁺and Sr²⁺.This specific binding event can be recognized by a natural fluorophore of hypericin with a lighting-up fluorescence response.Interestingly,inverting the polarity of the most 3'G in htG4 can sensitize the Ba²⁺response with the retaining Ba²⁺specificity and K⁺tolerance.This polarity inversion of htG4 causes a G4conformation change in K⁺and the polarity-inverted htG4 tends to favorably dimerize in response to the Ba²⁺specific binding.To our knowledge,this is the first report that polarity inversion of G4 can be applied to construct a selective Ba²⁺sensor with K⁺tolerance.Our findings will open a new way to conveniently regulate the G4conformation and stability by polarity inversion towards developing high-performance sensors.2.Ligand induced self-structuring of thymine-rich DNA into a parallel supramolecular fluorescent nanoassembly.The effective construction of DNA structures through small molecule ligands plays a very important role in the development of new DNA-based fluorescent nano-assemblies with ideal properties.In contrast to studies on the interaction of adenine-rich DNA?ploy A?with small molecules,thymidine-rich DNA?ploy T?has been scarcely reported.In this work,we found that in a sodium ion solution,NIT can transform this randomly coiled ploy T into the functional parallel duplex structure and form the supramolecular assembly of ligands.Because NIT has the planar structure of aromatic rings and coplanar substituents,as well as aggregation-induced emission?AIE?properties,it can be inserted between base pairs of duplexes through intercalation.Isothermal titration calorimetry?ITC?data shows that NIT and thymine are assembled in a 2:3 mode in the duplex.Moreover,using gold nanoparticles as the color output signal,we can intuitively observe that NIT induces the assembly of single-stranded ploy T into parallel duplexes.Our findings will provide a completely new approach for the development of DNA-based novel supramolecular fluorescent nanoassembly.