Research On Electrochemical Biosensors Based On MXene Three-dimensional Nanocomposites And Target Signal Amplification

The types and expression levels of biomarkers are closely relevant to the formation and development of carcinogenesis.The establishment of sensitive and effective early tumor biomarker detection mechanism is significate for the diagnosis and treatment of diseases.As a new type of biosensor,electrochemical biosensor has been widely used for its advantages of low cost,simple operation,fast response and high sensitivity.Ti₃C₂T_xMXene nanosheet is a layered two-dimensional material with good hydrophilicity and large surface area.Ti₃C₂T_xMXene hydrogels(MXH)are a class of three-dimensional nanomaterials capable of rapid electron and ion transfer.All of them could provide a large of binding sites for metal nanoparticles,DNA and other biomolecules to form a sensing substrate.In recent years,target signal amplification strategies(enzyme aided cascade target recycling,DNA Walker,metal nanoparticles/dendrimer nanocomposites)are used in biosensors.The purpose of this research is to use Ti₃C₂T_xMXene as the basic material to obtain Au NPs/MXene three-dimensional composite material through reducing agent reduction or MXene in-situ reduction,which can be used as a substrate to enhance the signal and to construct an efficient and sensitive electrochemical biosensor combined with the target signal amplification strategy.Based on the above ideas,the following research work has been carried out:1.Electrochemical biosensor based on gold nanoparticles/Ti₃C₂T_xMXene three dimensional nanocomposites and exonuclease III assisted cascade target cyclingUsing sodium citrate as a reducing agent and reducing chloroauric acid to obtain gold nanoparticles(Au NPs),Ti₃C₂T_xMXene with a layered structure was used as a substrate material to immobilize Au NPs to obtain a Au NPs/Ti₃C₂T_xMXene.Then the capture DNA(C-DNA)is covalently attached to the surface of Au NPs.The 3'end of C-DNA was modified with methylene blue(MB)signaling molecule,which produced a large initial DPV electrochemical signal(I_d).In the presence of the miRNA-155,target and C-DNA form a double stranded structure.Then,Exo III digests the 3'end of the C-DNA to release electrochemical signal molecules from the electrode surface,causing the signal to"turn off"(the final signal is denoted as I_h).Through Exo III-assisted target cascade shearing,resulting in a miRNA-155 target molecular chain releasing multiple C-DNA signaling molecular chains under certain conditions,thereby significantly amplifying the prepared biosensor.The peak current difference(?I=I_d?I_h)above,realizes the sensitive and effective analysis of target molecules.2.Electrochemical sensor based on in situ reduction of Au nanoparticles by Ti₃C₂T_xMXene and cascade signal amplification strategyThrough the in-situ reducibility of Ti₃C₂T_xMXene,gold nanoparticles(Au NPs)can be formed.By DNA walker strand displacement induced multiple DNA(product DNA)release and enzyme-assisted cascade signal amplification strategy,ultra-sensitive detection of target miRNA-21 is achieved.First,using the reducibility of MXene,Au NPs were formed in situ on the Ti₃C₂T_xMXene layer to obtain Au NPs/Ti₃C₂T_xMXene composite material,which is not only used to load capture DNA(C-DNA)to promote DNA hybridization,but also provide large electrocatalytic activity of(111)host crystal,which greatly improves the electrochemical signal of methylene blue(MB).In addition,in the presence of the target miRNA-21,the DNA Walker strand undergoes a strand displacement reaction,which leads to the release of multiple DNA fragments(p-DNA).The released multiple DNA fragments can be captured by the C-DNA of Au NPs/MXene/Au E and trigger the Exo III-assisted cascade shearing the C-DNA to further amplify the electrochemical signal.Through the cascade signal amplification strategy,the intensity of the current response is enhanced to improve the sensitivity of the detection result.3.Electrochemical sensing of three-dimensional self-assembled gold nanoparticles/MXene hydrogelGraphene oxide as the co-reactant and ethylenediamine as the crosslinking agent,the two-dimensional Ti₃C₂T_xMXene sheet is gelled into a three-dimensional structured hydrogel,and Au NPs were reduced in situ on the Ti₃C₂T_xMXene hydrogel to form a three-dimensional self-assembled Au NPs/Ti₃C₂T_xMXene hydrogel,which was used as a base material for loading hairpin DNA(hp DNA)probes to improve DNA hybridization.Au NPs with(111)crystal plane provides high electrocatalytic activity,thereby significantly improving methylene blue(MB)electrochemical signal,where MXenehydrogel acts as a reducing agent.In addition,in the presence of the target miRNA-122,the target opens the hairpin structure of hp DNA,and then polyamide amine dendrimer(PAMAM-encapsulated Au NPs(Au DNCs)and H-DNA conjugates(H-DNA/Au DNCs nanocomposite materials)act as an effective electrochemical label undergoes a sandwich reaction with the target,hp DNA to generate MB electrical signals.First,the hp DNA probes were fixed on the surface of the gold electrode.In addition,hp DNA and S-12 DNA were immobilized at the same time,which the density of hp DNA probes on the surface of the gold electrode could be precisely controlled,thereby providing high amplification efficiency and improving the sensitivity of detection.