Synthesis And Sensing Application Of Novel DNA Mediated Metal Nanoclusters

With the development of nanotechnology,nanomaterials have been widely used in environmental and biological fields due to the unique physical and chemical properties such as electronic,optical,catalytic and magnetic propertie.Various fluorescent nanomaterials with excellent fluorescent properties have been developed,such as quantum dots,metal nanomaterials,etc.Compared with traditional fluorescent dyes,new fluorescent nanomaterials overcome the shortcomings of poor stability,easy photobleaching,narrow excitation spectrum,broad emission spectrum,tailing and so on.Fluorescent nanomaterials are mainly synthesized by top-down or bottom-up methods.Template-mediated biomineralization has been favored by researchers because of its advantages such as simple synthesis,low cost,large Stoker shift and good biocompatibility.Nucleic acid molecule is an excellent template for synthesis of Metal nanocluster due to its controllability,encodability and easy modification.However,nucleic acid mediated metal nanoclusters are mainly from DNA templates,and there are few or no reports on RNA templates.On the other hand,the fluorescence conversion of DNA templated silver nanoclusters(DNA-AgNCs)is lacking.In this thesis,we aim to explore the the template ability of DNA/RNA chimeric chains for fluorescent copper nanoclusters(Cu NCs),and the influence of different proximity sequences on the spectral conversion of DNA-AgNCs.And two new nano-fluorescent probes for the analysis of environmental pollution markers(biological proteins and heavy metal ions)have been developed.Carry out the following work specifically:(1)DNA/RNA chimera-templated copper nanoclusters for label-free detection of reverse transcription-associated ribonuclease H.A DNA/RNA chimeric strand was designed and annealed at a high temperature to form a hairpin structure,which became a template for the synthesis of copper nanoclusters(Cu NCs).Cu NCs were synthesized by adding copper ions and sodium ascorbate.Compared with the copper nanoclusters synthesized by pure DNA template,DNA/RNA templated Cu NCs had similar fluorescence properties,stability and particle size.These results indicated that the chimeric DNA/RNA was also good template for fluorescent Cu NCs.Furthermore,the DNA/RNA templated Cu NCs were designed as a label-free fluorescent probe for detecting RNase H.When the target is not present,the chimeric template can synthesize Cu NCs,which exhibit strong fluorescence.On the contrary,in the presence of the target,the hairpin structure was destroyed,Cu NCs could not be synthesized and showed no fluorescence.The quantitative detection of RNase H was achieved by the change of fluorescence.This method not only provides a new template for the synthesis of DNA-MNCs,but also provides a reliable tool for sensitive detection of RNase H and high-throughput screening of anti-RNase H drugs.(2)Sequence proximity induced spectral conversion of silver nanoclusters.The effects of complementary chains containing A/T/G/C as protruding end sequences on the fluorescence spectrum of AgNCs were investigated.It is found that the proximity of G/C sequence can induce the spectrum change of the yellow fluorescent AgNCs to the red fluorescent AgNCs,and the excitation/emission spectrum changes from 500/560nm to 570/620 nm,while the A/T sequence only affects the fluorescence intensity of AgNCs.Furthermore,we also investigated the influence of the number and order of G/C on the spectral changes of AgNCs,and found that when the number of G/C is?5 and the order is continuous,the yellow silver nanoclusters will be converted into red silver nanoclusters.The transformation mechanism was further characterized and confirmed by spectroscopy and transmission electron microscopy.After hybridizing with the yellow AgNCs,the complementary sequence can synthesize a new fluorscent AgNCs,which induced the fluorescence spectrum change of the yellow AgNCs.At the same time,the guanine has the lowest oxidation potential,which can change the surface charge of the silver nanoclusters,and increases the potential of the silver nanoclusters.This may be the reason why the fluorescence intensity of AgNCs induced by G base is stronger than that induced by C base.We also demonstrate the generality of the phenomenon by changing the complementarity of the sequence.This finding will provide the basis for the construction of ratiometric fluorescent probe and the possibility for accurate detection of targets in complex samples.(3)A ratiometric fluorescent probe based on the spectral conversion of silver nanoclusters for monitoring mercury ions in wastewater.Based on the above findings,and the special structure(T-Hg-T)formed between the thymine and mercury ions,we developed a ratiometric fluorescent probe for the detection of mercury ions.When mercury ions are present,the target induce the formation of T-Hg-T structure and hybridization of the two sequences.The poly G sequence are close to the DNA-templated AgNCs and induced the fluorescence spectrum changes of the AgNCs.On the contrary,in the absence of mercury ions,the template chain and complementary sequence could not form a T-Hg-T structure,and the fluorescence spectrum of DNA-AgNCs did not changed.So,the concentration of mercury ions can be related to the changes in the fluorescence ratio of emission peak(F₆₂₀/F₅₆₀)of AgNCs.This method provides a tool for the accurate detection of mercury ions in complex samples and novel ratiometric sensing application of silver nanoclusters.