The Fabrication Of DNA Sensors Based On Lanthanide Metal-organic Frameworks And Their Analytical Applications

Specific sequences of DNA can specifically recognize different targets such as complementary DNA,metal ions,and proteins.DNA is easy to synthesize and modify.As a recognition element,single-stranded DNA with stable and predictable structure has been widely applied to the construction in biosensors.Besides unique optical properties,on the other hand,lanthanide metal-organic frameworks possess the advantages of simple synthesis and good thermal stability,and therefore show great potentials in the field of biosensing.Inspired by these outstanding properties,we developed several DNA sensors based on lanthanide metal-organic frameworks in this thesis.The main contents are summarized as follows:1.Luminescent lanthanide metal-organic frameworks for DNA colorimetric sensingIn this work,we labeled 6-carboxy fluorescein?FAM?at the end of single-stranded DNA?ssDNA?,obtaining FAM-DNA probe with strong green fluorescence.A kind of lanthanide metal-organic framework?Eu/BTC?with red fluorescence was synthesized by using lanthanide europium ion(Eu³⁺)as the metal node and trimesic acid?BTC?as the ligand.Because of the structure of BTC is rich in ?-bond,it provides a conjugated ?-electron system and the intrinsic fluorescence quenching ability of the metal cations.Thus,Eu/BTC could reasonably absorb ssDNA,and quench the fluorescence of FAM.However,upon the introduction of complementary target DNA?t DNA?,FAM-DNA would detach from the surface of Eu/BTC to form a double-stranded DNA?dsDNA?,leading to the fluorescence recovery of FAM.In the process of the interaction between the FAM-DNA probes and Eu/BTC?adsorption and desorption?,the red fluorescence of Eu/BTC remained constant.Therefore,we designed a colorimetric sensor for the detection of DNA.This sensor has a good linear relationship between the fluorescence intensity at 520 nm and tDNA concentration in the range of 0.5-40 nM,with the detection limit of 0.09 nM,and can be used to detect DNA in serum samples.2.DNA sensor based on multiple valent cerium metal organic frameworks for colorimetric detection of mercury ion.In this work,lanthanide cerium ion(Ce³⁺)was used as the metal node and trimesic acid?BTC?was used as the organic ligand to synthesize the lanthanide metal-organic framework?Ce/BTC?.Then we use the mixed solution of NaOH-H₂O₂ to partially oxidize the Ce/BTC,which leads to the formation of multivalent cerium metal organic frameworks?MVCM?with oxidase-like catalytic activity.MVCM can catalyze colorless TMB to ox TMB with blue color.However,upon the introduction of thymine?T?-rich single-stranded DNA?T-DNA?,the oxidase-like activity of MVCM can be inhibited due to the adsorption of T-DNA on the surface of MVCM.Because Hg²⁺ can recognize T-T base pair to form T-Hg²⁺-T compounds,the presence of Hg²⁺ will lead T-DNA to detach from MVCM as the formation of double-stranded DNA,recovering the catalytic activity of MVCM.Based on these facts,we designed a DNA sensor based on multivalent cerium metal organic frameworks for the detection Hg²⁺.This sensor has a good linear relationship between the absorbance intensity at 655 nm and Hg²⁺ concentration in the range of 0.2-6 ?M,with the detection limit of 28 nM,and can be used to detect Hg²⁺ in tap water samples.3.Multivalent cerium metal organic framework-based DNA sensor for detection of alkaline phosphatase and the fabrication of logic gateIn this work,we labeled 6-carboxy fluorescein?FAM?at the end of single-stranded DNA?ssDNA?,obtaining FAM-DNA probe with strong green fluorescence.The MVCM was used as the quenching agent of FAM-DNA.Upon the introduction of pyrophosphate?PPi?,FAM-DNA detach from the surface of MVCM,resulting in the recovery of the FAM fluorescence.This is due to the binding ability of PPi and MVCM is stronger than that of FAM-DNA and MVCM.However,in the presence of alkaline phosphatase?ALP?,PPi can be hydrolyzed into orthophosphate?Pi?.The binding ability of Pi and MVCM is weak,which cannot lead to the detachment of FAM-DNA from the surface of MVCM,and therefore FAM fluorescence was quenched by MVCM.Based on these facts,we designed a DNA sensor for the detection of ALP.This sensor has a good linear relationship between the fluorescence intensity at 520 nm and ALP concentration in the range of 5-40 U/L,with the detection limit of 0.42 U/L,and can be used to detect ALP in serum samples.In addition,we fabricated the inhibit logic gate by using PPi and ALP as input signals,the intensity of the fluorescence as output signal.