Study On Novel Photoelectrochemical Biosensing Of Prion And Ribonucleic Acid

Photoelectrochemical sensor is a kind of device to detect the concentration of target object based on the photoelectric transformation characteristics of semiconductor material.Compared with electrochemical sensors,photoelectrochemical sensor has different forms of excitation energy and detection signal endow it with lower background and higher sensitivity.Photoelectro chemical biosensor has attracted much attention because of its good ability to detect biomolecules.Prion diseases are a kind of typical nervous system variant disesse.Infectious mink encephalopathy,bovine spongiform encephalopathy and pruritus of sheep are common animal prion diseases.In addition,the human prion diseases mainly include creutzfeldt-jakob disease,prion dementia or prion dementia with spastic paraplegia,gerstmann-strauss-scheinker syndrome and so on.The transformation of conformation from normal cell morphology?PrP^C?to infectious form(PrP^Sc)is the key factor in the pathopoiesis of prion disease.The concentration of prion protein in human body is very low.Therefore,it is necessary to develop a rapid and sensitive sensing method to detect prion for the prevention and treatment of prion diseases.Nucleic acids are widely found in all animal,plant cells and microorganisms.Nucleic acid is the main mediator of genetic information and has specific structure.According to the different chemical composition and nucleotide sequence,nucleic acids can be divided into DNA and RNA.MicroRNAs?miRNA?are a class of non-coding RNA found in eukaryotes.Recent studies have found that miRNA expression is associated with various cancers,it plays a decisive role in the process of tumor formation.Therefore,the development of highly effective and sensitive nucleic acid sensors have profound research significance and value.In this thesis,we used photoelectrochemical biosensors to realize the sensitive detection of prion and microRNA:?1?A simple and“signal-off”PEC immunosensor was developed for sensitive assay of prion protein.Taking the MPA-capped CdTe QDs as photocathodic materials and GOx as a catalyst to consume the dissolved O₂ and to in-situ generate H₂O₂.The consumption of the dissolved oxygen and the deterioration of the PEC properties of the photocathodic materials?MPA-CdTe quantum dots?result in the decrease of the photocurrent of the PEC platform.Under the optimal conditions,the proposed immunosensor shows a good analytical performance for prion detection.Two linear response ranges from 1 pg mL^-11 to 50 pg mL^-11 and from 50 pg mL^-11 to 1000 pg mL^-1can be observed with a low detection limit of 0.73 pg mL^-1?3??.By changing the specific antibody,this strategy could be easily extended to detect the infectious isoform of prion(PrP^Sc)and other proteins.?2?With the aid of exonuclease?Exo III?,the method of amplifying the detection signal through nucleic acid chain cycle realizes the detection of miRNA-21.The part of Initiate B generated in the cycle was paired with the Capture-DNA fixed on the surface of the photoelectric material,meanwhile,the DNA base sequence rich in Cytosine binding with silver ions to form C-Ag⁺-C and paired with the other end of Initiate B.In the presence of Na₂S,the semiconductor Ag₂S was generated mismatched with energy level of the photoelectric substrate?CdS/TiO₂?,reducing the photoelectric current.This PEC nucleic acid sensor provides sensitive and fast detection of miRNA-21 with a linear range of 0.5 fM-1 nM and a detection limit as low as 0.28 fM?S/N=3?.The sensor also has excellent selectivity and reproducibility.?3?A simple“signal-on”miRNA-21 photoelectrochemical?PEC?detection method is designed based on the composite material of SnO₂ and Au/g-C₃N₄ as photoelectric material.On the basis of nucleic acid base different strength pairing ability,building a nucleic acid chain cycle amplification strategy.Initiate B from the process of cycle can hybridize with Capture-DNA,with the participation of H₁ and H₂,multiple Y-type phosphate skeleton structure was formed on the electrode surface for introducing the hexaammineruthenium chloride?[Ru?NH₃?₆]Cl₃?on the electrode surface.Using the sensitization effect of[Ru?NH₃?₆]³⁺to detect miRNA-21,the linear range is 0.1 fM-1 nM and the detection limit is as low as 0.033 fM?S/N=3?.