The Application Of Functionalized Metal-Organic Frame Materials(MOFs) And Biomagnification Techniques In Electrochemical Biosensors

Recently,electrochemical biosensors have been widely used in bioassays,food analysis,environmental monitoring,and clinical diagnostics,due to their high analytical speed,good selectivity,low cost,high sensitivity,miniaturization of instruments,and ease of operation.In order to improve the sensing performance and further increase the sensitivity,various signal amplification techniques have recently been used for the construction of electrochemical biosensors.Among them,functionalized metal-organic framework materials?MOFs?have high specific surface area,regular order and adjustable pore size and shape,as well as easy functionalization and other characteristics,and become very versatile materials with promising applications,which offered a new way for biosensors provide.In addition,in recent years,a variety of biomagnification techniques have also been widely used in biosensors to improve sensing performance.In this paper,novel high-sensitivity electrochemical biosensor were constructed by combining the superior performance of MOFs materials and biomagnification techniques.Part 1 Thrombin Aptasensor Enabled by Pt Nanoparticles-Functionalized Co-Based Metal Organic Frameworks Assisted Electrochemical Signal AmplificationMetal-organic frameworks?MOFs?composed of inorganic ions and polytopic organic ligands have attracted enormous interest since their inherent large surface areas,uniform but tunable cavities,and tailorable chemistry which were gradually used as catalysts but rarely exploited as nanocarriers in biosensors.In this work,a Pt nanoparticles-functionalizedCo-basedmetalorganicframeworks?PtNPs@Co-MOFs@PtNPs?was synthesized and applied in electrochemical aptasensor for thrombin?TB?detection.Frist,the Co?II?MOFs@PtNPs were prepared via the mixed solvothermal method,which were consisted of inner Pt nanoparticles?PtNPs?encapsulated by aminofunctionalized Co?II?MOFs materials.Following that,another PtNPs were absorbed on the surface of Co?II?MOFs@PtNPs,resulting in the formationofPtNPs@Co?II?MOFs@PtNPsnanocomposite.The PtNPs@Co?II?MOFs@PtNPs nanocomposites with a large surface area were implimented as nanocarriers to immobilize a mass of TBA II for the formation of the TBA II bioconjugates.Moreover,the PtNPs@Co-MOFs@PtNPs nanocomposites could directly use as redox tags for charge-generating.Furthermore,in the presence of H₂O₂,the PtNPs@Co?II?MOF@PtNPs could effectively catalyze H₂O₂ decomposition with improvement electron transfer of redox probe,resulting in electrochemical signal amplification.Based on the above superior advantages,TB was determined in the concentration range from 0.1 pmol/L to 50 nmol/L with a detection limit of 0.33fmol/L.Part 2 Hg²⁺Electrochemical Biosensor Based on Target Triggered Exonuclease III-Assisted Dual Cycle Amplification and Tetrahedron DNA Nanostructures as Signal Molecule CarrierAccording to reports,the enzyme-aided target recycling strategy has been used to develop sensitive and selective detection of Hg²⁺in which cleavage activity of polymerase and nicking endonuclease on DNA duplexes with T-Hg²⁺-T base pairs was inactivated to released for Hg²⁺and initiated a new cycle to amplify response signal.Unfortunately,the polymeras-assisted Hg²⁺recycling was primer-dependent and the nicking endonuclease-based Hg²⁺recycling was sequence-specific,which limits its application.Significantly,Exo III was used because it was no specific recognition site and primer extension required.In this work,a novel Hg²⁺electrochemical assay was presented based on target triggered Exo III assisted dual cycle amplification and tetrahedron DNA?TDNA?nanostructures as efficient signal molecules carrier.In the presence of the target Hg²⁺,Hg²⁺triggered T-rich termini binding to reveal3?-hydroxyl termini of duplex DNAs,which could activate Exo-III digestion.More importantly,by using the tetrahedron DNA?TDNA?nanostructures as carriers for loading a large amount of thionine?Thi?,a remarkable electrochemical signal was obtained.Under optimal conditions,the developed electrochemical biosensor performed the linear range from 0.1 pmol/L to 500 nmol/L with a detection limit of 33fmol/L for Hg²⁺determination.This strategy designed a novel electrochemical biosensor,which offered a new way for metal ion detection,showing potential applications in biological samples and environmental monitoring.Part 3 Sensitive and Selective VEGF_-165165 Detection Based on Hyperbranched Rolling Circle Amplification?HRCA?and Phosphate ions Induced Deposition of Redox PrecipitatesVascular endothelial growth factor-165(VEGF_-165),a glycoprotein produced by skin keratinocytes,fibroblasts,and macrophages,is one of the main promoters of angiogenesis.Therefore,the VEGF_-165165 overexpression or downregulation is associated with different diseases,including gastrointestinal cancer,patients with breas,ovarian cancer,lung cancer and urinary tract tumors,which has been regarded as an important biomarker for diseases diagnosis in clinical.Recently,different analytical methods to quantitatively analyze VEGF_-165165 have been reported,for instance,optical methods,surface-enhanced Raman scattering?SERS?,enzyme-linked immunosorbent assays?ELISAs?and etc.However,most of them are high cost,time-consuming and tedious.Therefore,it is highly desirable to develop an simple and efficient method for sensitive VEGF_-165165 detection.Herein,based on HRCA and phosphate ions induced deposition of redox precipitates,a novel electrochemical aptasensor for VEGF165was reported with high sensitivity and accuracy for the first time.We indirect detect based on tracing phosphate ions?Pi?generated during HRCA but direct detect the amplified DNA.Pyrophosphate?PPi?as the byproduct of HRCA was hydrolyzed into Pi by the alkaline phosphatase?ALP?,the produced PPi would be hydrolyzed into 2equiv of Pi,which could further react with acidic molybdate to form a molybdophosphate precipitate on the electrode surface,and was used as an electrical mediator for electrochemical signal.Under optimal conditions,the developed electrochemical biosensor performed the linear range from 0.005 ng/mL to 40 ng/mL with a detection limit of 1.7 ng/mL for VEGF_-165165 determination.Significantly,the assay approach also opens a new opportunities based HRCA and phosphate ions induced deposition of redox precipitateshad for sensing biomolecules,showing potential applications in clinical diagnostics.