Stuides On Photoelectrochemical Biosensors For Detection Of MiRNA

MicroRNAs?miRNAs?are a new class of highly specific and sensitive tumor markers.Detection of very low concentrations of miRNA in the human body is important for precancerous lesions,early diagnosis and early warning of tumors,and early treatment of neoplastic diseases.In this work,three kinds of photoelectrochemical biosensors for ultrasensitive of miRNA were developed.This thesis research work mainly includes the following sections:1.Faraday cage-type electrochemiluminescence biosensor based on multi-functionalized graphene oxide for ultrasensitive detection of miRNA-21A Faraday cage-type electrochemiluminescence?ECL?biosensor for ultrasensitive detection of cancer-associated miRNA-21 was constructed based on Fe₃O₄@Au magnetic nanoparticles?Fe₃O₄@Au MNPs?and multi-functionalized graphene oxide.The capture unit?Fe₃O₄@Au MNPs-cDNA?was prepared by immobilizing capture DNA?cDNA?on Fe3O4@Au MNPs,while the multi-functionalized graphene oxide acted as the signal unit??sDNA&luminol?@GO?.In this biosensor,the capture unit,which was used to catch the miRNA-21,could be easily attracted onto the magnetic glassy carbon electrode surface.After the hybridization of miRNA-21 with the capture unit,the signal unit was further hybridized to form a Faraday cage-type structure,in which the signal unit was directly fixed onto the electrode surface,resembling a huge net and even becoming a part of the electrode surface.All luminol molecules labeled on the signal unit could take part in the electrode reaction,thus greatly enhancing the ECL signal.The ECL intensity was found to increase with the logarithm of miRNA-21 concentrations from 1 fM to 10 pM with a detection limit of 0.3 fM.In addition,this proposed Faraday cage-type ECL biosensor can be used for practical analysis of miRNA-21 in human serum,providing an ultrasensitive detection platform for microRNA in clinical diagnosis.2.An Ultrasensitive Faraday cage-type electrochemiluminescence assay for femtomolar miRNA-141 via graphene oxide and hybridization chain reaction-assisted cascade amplificationIn this study,a novel electrochemiluminescence?ECL?biosensor for sensitive detection of femtomolar miRNA-141 was constructed on the basis of Faraday cage-type strategy via graphene oxide?GO?and hybridization chain reaction?HCR?-assisted cascade amplification.A capture probe?CP?was immobilized on Fe₃O₄@SiO₂@Au nanoparticles as capture unit,which could catch the miRNA-141,and the immobilization of the signal unit(Ru?phen?₃²⁺-HCR/GO)was allowed via nucleic acid hybridization.The prepared biosensor exhibited two advantages for signal amplification:firstly,GO could lap on the electrode surface directly,extending Outer Helmholtz Plane?OHP?of the sensor due to the large surface area and good electronic transport property;secondly,HCR-assisted cascade amplification was designed by anchoring all HCR products on the GO surface,then embedding Ru?phen?₃²⁺as a signal readout pathway.All these signal molecules could take part in electrochemical reactions,thus further enhancing the ECL signal drastically.Therefore,the proposed sensor constructed by integrating HCR with Faraday cage-type strategy displayed an ultrasensitive detection platform for the miRNA-141 with a low detection limit of0.03 fM.In addition,this proposed biosensor provides an effective way for analysis of other microRNA.3.The surface-enhanced Raman scattering biosensor based on multiple signal amplification strategy for ultrasensitive detection of miRNA-141A surface-enhanced Raman scattering?SERS?biosensor based on AuNPs nanowires vesicles?AuNWs?and hybridization chain reaction?HCR?was constructed for ultrasensitive detection of cancer-associated miRNA-141.In the system,trigger probe?TP?fixed onto the surface of AuNWs will induce the HCR amplification to form the double-stranded DNA?dsDNA??AuNWs/HCR?,which can greatly improve the signal intensity.And then,amounts of Ag nanoparticles reduced on the AuNWs and dsDNA?AgNPs@AuNWs/HCR?can further enhance the signal output.In addition,R6G as a kind of common probe molecule,can adsorb onto the AgNPs to form the signal unit.Fe₃O₄@AuNPs labelled capture probe?CP?was used as the capture unit.And based on the theory of base-pairing pairing,it can form a“sandwich”complex with signal unit in presence of miRNA-141,resulting in the direct separation for SERS detection.After three times amplification of the signal mentioned above,SERS signal of miRNA has been tremendously improved.Also,the highly sensitive and specific detection of miRNA-141 has a detection limit as low as 0.03 fM.