A Study Of The Construction Of Electrochemical Biosensor Based On MOFs Composite Materials And Novel Signal Amplification Technology

Electrochemical biosensor is a new kind of device in which the concentration of target can convert into a relevant electrochemical signal（including current,potential,impedance）through a biological component.Among them,the familiar biological components usually have a specific recognition effect with the target,such as antigen,antibody,enzyme,cell and organelle.Thus,electrochemical biosensor has been proven wonderful by virtue of its fascinated virtues,including strong stability,high sensitivity and good selectivity,and also widely used in clinical diagnosis,food analysis,environmental monitoring and other fields.Due to the fact of small signal caused by biometric reactions,it is particularly important to enhance the detection performance of electrochemical biosensors by using suitable signal amplification strategies.Metal organic frameworks（MOFs）have become an effective electrochemical signal amplification method owing to their large surface area and porous structure.Meantime,DNA Walker,as a novel molecular machine that can move autonomously within the nanometer scale,has also been increasingly used to construct efficient signal amplification strategies.Based on the above exploration,this study constructed three signal amplification sensing platforms based on MOFs and DNA Walker for the determination of cancer biomarkers.The major contents are concluded as follows:1.In this work,a facile electrochemical“signal on”biosensing platform with a near-zero background signal were developed for a sensitive assay of mi RNA-10b based on the in situ generation of bimetallic CuFe prussian blue analogue（CuFe-PBA）assisted by three-dimensional DNA walker signal amplification strategy.Specifically,the bimetallic CuFe-PBA was used as instant catalyst,which possessed both abundant redox active sites and mixed conductivity within the cyanide-bridged porous structure,markedly improving the sensitivity of the platform.With target introduction,the DNAzyme strand was lost of protection and further hybridized with substrate strand to form a Mn²⁺-specific DNAzyme,resulting in substrate strand digestion and assistant strand release from MB.Furthermore,the released assistant strand was anchored on the surface of GCE and further incubated with compement DNA labelled-NMOF@Cu²⁺probe.Eventually,a large number of CuFe-PBA were generated on the electrode with the help of K₃[Fe（CN）₆],which can catalyze the 4-CN precipitation without H₂O₂,thereby resulting in the increase of resistance of the platform.Under the optimal conditions,the proposed biosensor exhibited good analytical performance in a dynamic working range from 0.8 pM to 250 pM with a low detection limit of 0.5 pM.2.The aim of this study was to develop a novel electrochemical biosensor based on three-dimensional（3D）DNA walker and MOF-Fe²⁺-regulated instant generation of Turnbull’s blue（TB）,for the highly sensitive and efficient detection of cancer biomarker miRNA.And 3D DNA walker was served as a signal amplification method.Unlike the traditional amplification methods,3D DNA walker has higher walking efficiency and signal amplification capability.In the process of assembling the biosensor,the H1（DNA tracks）was immobilized on the magnetic beads（MBs）for capturing the biomarker miRNA-21（walking strand）,the H2 was decorated by glucose oxidase（GOx）for propelling strand displacement reaction.In the presence of miRNA-21,3D DNA walker was activated,and abundant GOx on H2 was introduced into the surface of the MBs to amplify the biosensor signal.Meanwhile,glucose was catalyzed hydrolysis by GOx to produce hydrogen peroxide（H₂O₂）,which was used oxidize Fe²⁺to Fe³⁺in MOF-Fe²⁺on the surface of GCE to further inhibit the formation of TB.The results indicate that the biosensor showed a broad linear response from 0.001 to 100 pM and the low detection limit is 0.3 fM.Moreover,the biosensor was capable of detecting miRNA even in human serum samples,demonstrating potential application in disease diagnostics and clinical medicines.3.In this work,we reported the preparation and characterization of the ferrocene-encapsulated Zn zeolitic imidazole framework（Fc@ZIF-8）hybrid materials as well as its application for alkaline phosphatase（ALP）novel electrochemical sensing system.Specifically,we synthesized the Fc@ZIF-8 composite by simple one step self-assembly of Zn²⁺and 2-methylimidazole,and the morphology,structure,element and electrochemical properties were characterized by scanning electron microscopy,powder X-ray diffraction and differential pulse voltammetry experiments.The results showed that the obtained Fc@ZIF-8 has typical rhombic dodecahedron morphology with an average particle size of about 100 nm.In the presence of the target ALP,the substrate 2-phospho-L-ascorbicacid trisodium salt（AAP）was catalytically hydrolyzed into L-ascorbic acid（AA）,resulting in the decomposition of Fc@ZIF-8 modified on the electrode,and followed,encapsulated Fc was released in the electrolyte.As a result,the current of Fc@ZIF-8/GCE was decreased obviously.Taking advantage of Fc@ZIF-8 cleavage reaction,the proposed electrochemical sensor showed a good linear relationship from 1 to 100 U/L,with a low detection limit of 0.38 U/L.Importantly,the sensor possessed favourable selectivity,reproducibility,and stability.The further detection of ALP in human serum samples indicated its applicability in the clinical diagnosis and biomedical research.