| Developing simple and easy-to-operate sensing platform for the sensitive and reliable target analysis would provide enormous opportunities to boost the applications in clinical biomedicine and disease diagnosis.In this thesis,two novel electrochemical bio-DNA sensors based on hybridization chain reaction,entropy-driven,dual-signal detection and dual-mode detection strategies were constructed and their detection performance was investigated using HIV DNA and Micro RNA 21 as models.1.Herein,a DNA polymerase-powered self-propelled DNA walking strategy was developed to achieve one-step,dual-signal and amplified nucleic acid detection.The sensing platform was fabricated easily by immobilizing two hyrbid probes on electrode surface.Each hybrid probe was consisted of a DNA hairpin and a redox reporter-labelled signal strand.The HIV DNA fragment was used as a model target.It could trigger the DNA polymerization cascade between two hairpins assisted by DNA polymerase,accompanying with the release of two signal strands from electrode surface for the concurrent responses of two electrochemical signals of methylene blue and ferrocene.The simultaneous dual-signal and amplified responses facilitated the sensitive and reliable analysis of target.The low detection limit toward target nucleic acid could reach 0.1 f M whether by methylene blue or ferrocene responses.It could also achieve the selective discrimination toward mismatched sequences and the application for target detection in a serum sample.The distinct features for current sensing strategy also include its autonomous one-step operation and no extra DNA reagents requirement for signal amplification except a DNA polymerase.Thus,it provides an attractive means for biosensor fabrication directing toward the reliable and sensitive analysis of nucleic acid or more analytes.2.Based on the target-initiated entropy-driven amplification strategy and the short-range burst of fluorescence by gold nanoparticles,a dual-mode "fluorescence-electrochemical" DNA biosensor was constructed for the one-step specific detection of Micro RNA 21.The nanoprobe was assembled on the surface of Au NPs by gold-sulfur bonding with a hybridization of biotin-labeled ss DNA(S1)and fluorescent group(FAM)-labeled ss DNA(S2)to construct a fluorescence-electrochemical DNA sensing interface.When the target is present,the entropy-driven amplification reaction can be triggered,the hybridized structure is no longer stable,Biotin is exposed and interacts with streptavidin(SA)on the glassy carbon electrode,generating a significant electrochemical signal;meanwhile the S2 strand with the fluorophore(FAM)is released into the solution and the fluorescence is restored.When the target is not present,the hybridization probe S1-S2 structure remains stable and neither fluorescence-electrochemical signal is present.This sensing method has a good selectivity and can be used for Micro RNA 21 detection in serum samples.The significant advantages of this strategy also include its high accuracy of dual mode,high sensitivity,and spontaneous amplified signal response.Therefore,this method is expected to provide new methods and strategies for accurate and reliable analysis of Micro RNA 21 and other mi RNAs in multiple disease settings. |
