Biological Affinity Induced Electron Transfer Disturbance Of MOFs/COFs For Electrochemical Label-free Biosensing Analysis

Metal-Organic Frameworks(MOFs)and Covalent organic frameworks(COFs)are a type of novel three dimensional(3D)porous materials with high porosity,specific surface area,special topological structure,unique electrical properties etc.therefore,they are widely applicated in electrochemical sensors.However,the traditional methods for preparing MOFs and COFs are complicated,which limits their applications.In this paper,electroactive MOFs and COFs were directed modified on the surface of electrode by electrochemical in-situ self-assembly methods,and its was used as platform for detection of biomarkers.The main research work are as follows:(1)In this chapter,a simple but ultraselective electrochemical DNA biosensor based on MOF had been designed to detect target miRNA-21 related to liver cancer,which combines the signal amplification of Exo Ⅲ enzyme-assisted target recycling with the immobilization-free electrochemical method.For the first time,electroactive copper-hexahydroxytriphenylene(Cu-HHTP)was modified on the surface of glassy carbon electrode(GCE)by two-step electrodeposition method.In the presence of miRNA-21,the probe DNA hybridizes with miRNA-21 to form a double-stranded structure(dsDNA),the dsDNA was recognized and cleaved by the Exo Ⅲ enzyme to produce quantities of DNA fragments.and then the DNA fragments were uptake into the pores of Cu-HHTP,leading to attenuation of the electrochemical signal of the fabricated biosensor.Through such a method,the miRNA-21 biosensor can be simply developed,and the concentration of miRNA-21 can be well determinated by monitoring the signal change of the biosensor.The fabrication process was characterized by X-ray energy spectroscopy(EDS),scanning electron microscopy(SEM),Raman spectroscopy,ATR-Fourier Infrared Spectroscopy(ATR-FTIR)and electrochemical methods.The experimental results confirmed the Cu-HHTP has been successfully synthesized and the sensor can detect miRNA-21 quickly and sensitively.Quantitative analysis showed that the target RNA could be detected range from 0.01 fM to 10 nM with the detection limits of 4.5 aM.The developed sensor also shows satisfactory results for the determination of miRNA-21 in the real serum sample andthe recoveries were in range of 97% to 105%.(2)In this study,a Exo III-powered DNA walker,based on a DNA-functionalized gold nanoparticle(DNA-AuNP),which moves along a three-dimensional(3D)DNA-AuNP for the electrochemical detection of liver circRNA—Has-circ-0005075(HcircRNA)are constructed and compared.We directed in-situ deposition of Cu-MOF-74 on the surface of multi-walled carbon nanotubes(MWCNT)modified GCE.In the presence of HcircRNA,the DNA1 hybridizes with target RNA to form a double-stranded structure(DNA-RNA),the DNA2 walks along the 3D track by cleaving DNA3 at each step,the DNA-RNA was also recognized and cleaved by the Exo Ⅲ enzyme to produce quantities of DNA fragments.and then the DNA fragments were uptake into the pores of Cu-MOF-74,leading to attenuation of the electrochemical signal of the developed biosensor.Through such a strategy,the HcircRNA biosensor can be simply fabricated,and the concentration of HcircRNA can be well determinated by monitoring the signal change of the biosensor.The fabrication process was characterized by ATR-FTIR and SEM etc.The results proved that Cu-MOF-74 was successfully synthesized on the modified electrode surface.Quantitative analysis showed that the HcircRNA could be detected range from 0.1 fM to 10 nM with the detection limits of 38 aM.The developed sensor also shows satisfactory results for the determination of HcircRNA in the real serum sample and the recoveries were in range of 96% to 103%,and the sensor showed satisfactory selectivity and stability.(3)A novel electrochemical cardiac troponin I(cTnI)sensor has been developed based on a novel electroactive ferrocene-based covalent organic framework(COF)—HHTP-BFc-BA.For the first,the COF was in-situ self-assembly modified on the gold electrode(AuE).The cTnI aptamer(TSA)were immobilized onto the surface of modified electrode by embedded into the holes of COF,and the new label-free immunosensor TSA/HHTP-BFc/BA/AuE was successfully developed.When the target cTnI was presented in solution to specific interact with TSA strands,and TSA falls off from the material,leading to the electrochemical signal remarkly change.Through such a method,the cTnI biosensor can be developed,and the concentrationof cTnI can be well detected.Different modified electrodes were characterized by SEM,ATR-FTIR,EDS,X-ray diffraction(XRD),atomic force microscopy(AFM)and electrochemical methods.All results confirmed that the sensor can quickly and sensitively detect cTnI.Under optimal conditions,the sensor can detect cTnI over a wide range from 10 fg/mL to 10 ng/mL with a detection limit of 2.6 fg/mL.When the sensor was applied to the detection of cTnI in actual serum samples,the recovery rate was 97.2% to 102.9%,and the results were satisfactory.