Interaction Of Thioflavin T And GA-Containing Parallel Duplex And Its Applications

Thioflavin T（ThT）,a benzothiazole dye,is firstly used as a fluorescent ligand specific for amyloid proteins.In recent years,it is found it could as a excellent ligand for recognition of G-quadruplexes in DNA field.However.some studies imply that ThT could give high fluorescence not only in G-quadruplexes,also in other structures such as duplexes and ATP aptamer.Hence,this work aimed to explore which structure or which sequence of DNA can efficiently enhance fluorescence intensity of ThT.The main contents and conclusions of this work are as follows:1.Firstly,we designed G-quadruplex forming sequence GGGTTA and its variants which might form G-quadruplex or other strutures interact with ThT and found that ThT can tightly bind non-G-quadruplex DNAs with several GA motifs and make them dimerized in a parallel double-stranded mode,accompanied by over 100-fold enhancement in the fluorescence emission of ThT.The introduction of reverse Watson-Crick T-A base pairs into these dimeric parallel-stranded DNA systems remarkably favors the binding of ThT into the pocket between G·G and A·A base pairs,where ThT is encapsulated thereby restricting its two rotary aromatic rings in the excited state.A similar mechanism is also demonstrated in antiparallel DNA duplexes where several motifs of two consecutive G·G wobble base pairs are incorporated and serve as the active pockets for ThT binding.2.Based on the interactions of ThT with GA-containing parallel duplexes,DNA-based metal sensors and devices are contrived.Combined C-Ag⁺-C and T-Hg²⁺-T interactions,we designed two GA-containing parallel duplexes including C-C and T-T mismatches as novel metal sensing platforms to detect Ag⁺ and Hg²⁺,respectively.The sensors both have good performances in sensitivity,selectivity and practicability.We also employed ThT as indicator and designed a DNA triplex containing GA motifs in its Hoogsteen hydrogen-bonded two parallel strands as a pH-driven nanoswitch,make it can switch ’Turn-off’ to ’Turn-on’ when pH from 8.0 change to 5.5,and it exhibit good reversibility.