Studies On Properties And Applications Of Fluorescent Probe Based On Nucleic Acids

Because of its high sensitivity,high selectivity,convenience,fluorescent probes has attracted much attention of researcher.In this thesis,silver nanoclusters with fluorescent properties were synthesized by using matched double-stranded DNA as template.A sensitive K+ sensor based on Hybrid-2 conformers G-quadruplex.A simple method for detection of melamine was developed based on Hybrid-1 conformers G-quadruplex.The main research contents and experimental conclusions are summarized as follows:1.Capability of ds-DNA duplex structure in growing fluorescent silver nanoclusters.Silver nanoclusters(AgNCs)have attracted wide interests in variant fields due to their easy synthesis and practical tunability in fluorescence properties.DNA has been generally used as the host to grow AgNCs due to the sequence-dependent fluorescence behavior.Actually,in such DNA,various ss-DNA segments that are structurally confined by the rigid ds-DNA counterparts have been used as the AgNCs' growth sites.However,whether the ds-DNA structure plays somewhat role in AgNCs' creation has not been well elucidated.Herein,we found that ds-DNA can also accommodate the growth of fluorescent AgNCs.The fluorescent AgNCs grown on ds-DNA should be separated each other and the G/C base pairs with right context sequences are the growth sites of fluorescent AgNCs.The intermediate A/T base pair among the continuous G/C ones seems to quench the growth of fluorescent AgNCs.For the repeat sequences,the fluorescence band position of AgNCs is not changed but the intensity is enhanced upon increasing the ds-DNA length,which is different from the results obtained with the previously reported ss-DNAs.AgNCs should be grown on the ds-DNA major groove,as convinced by the cytosine methylation experiment.Our work demonstrates that besides the ss-DNA role in defining AgNCs,one should also take into account the critical role of the ds-DNA segment in tuning the AgNCs'fluorescence property.2.Human telomeric hybrid-2-over-hybrid-1 G-quadruplex targeting and a selective hypersaline-tolerant sensor using abasic site-engineered monomorphism.Coexistence of the polymorphic hybrid-1 and hybrid-2 conformers for a given human telomeric G-quadruplex-forming sequence(htG4)complicates its fine structure identification and limits its application as a sensor element.With help from abasic site(AP site)-engineered htG4s serving as the monomorphic representatives of the two typical hybrid conformers,we found that thioflavin T(ThT)can selectively target the hybrid-2 conformer over the hybrid-1 counterpart in monomer and tandem htG4 molecules.The htG4 that solely adopts the monomorphic hybrid-2 conformer engineered by the AP site is most efficient in lighting up ThT fluorescence in K+ and a selective K+ sensor is realized with a remarkable hypersaline-tolerant capability that can work even in 30000-fold excess of Na+.At 600 mM Na+,the dynamic range for K+ detection can be extended to 30 mM with the limit of detection of 20 ?M.This is the first report on the fluorescence discrimination of these two hybrid conformers of htG4 although they have long been categorized with their characteristically structural topologies.Our work will attract much interest in the development of sensors based on the monomorphic htG4 conformer since such high performance in sensor development has not been previously achieved.3.Recognition of melamine based on human telomeric Hybrid-1 G-quadruplex and EpiMelamine is a chemical material used in industry.Due to the high nitrogen content of melamine,many businesses have added melamine to milk products to get a high protein content.Drinking mike containing melamine will make huge harm to the body.So,there is an urgent need for developing a sensitive melamine sensor.We found that at presence of melamine can keep the fluorescence of Epi at a high level.It can be predict that,this sensor will used wildely in the melamine detection.