Study Of New Electrochemical Detection Methods For MicroRNA And Arsenite

Electrochemical analysis methods have the advantages of sensitivity,simplicity,and economy,which are favored by researchers.Theoretically,the electrochemical sensor converts the target analyte signal into an electrical signal output through an electrochemical signal transducer.Functional nanomaterials not only can induce synergistic interactions between catalytic activity,electrical conductivity,and biocompatibility to accelerate signal transduction,but also show highly sensitive electrochemical biochemical and chemical sensing through specially designed signal amplification.Therefore,electrochemical sensing platforms based on nanomaterials have great potential for improving their sensing performance.The paper focus on improving the performance of electrochemical analysis and using the excellent properties of nanocomposites in electrochemical analysis to construct novel electrochemical detection methods for microRNA and arsenite（As（III））.The main researches are as follows:1.Based on the potential difference of the electron mediator on magnetic nanoprobes and target microRNA-triggered hybridization chain reaction（HCR）signal amplification technology,an electrochemical sensor for simultaneous detection of microRNAs was established.Firstly,two kinds of magnetic nanoprobes（DNA1/Fe₃O₄ NPs/Thi and DNA2/Fe₃O₄ NPs/Fc）were prepared.Because the electrochemical responses of the two magnetic nanoprobes are at different potentials（thionine（Thi）:-0.24 V,ferrocene（Fc）:0.46 V）,simultaneous detection of microRNAs was relized.In the presence of microRNA-141 and microRNA-21,the HCP1 and HCP2 immobilized on the surface of the electrode can hybridize with them,respectively,resulting in the conformational change of HCPs which triggers HCR for further capturing of corresponding magnetic nanoprobes.The HCR can greatly increase the binding sites of nanoprobes and Fe₃O₄ NPs can carry a large number of redox signals.This allows for the simultaneous detection of microRNA-141 and microRNA-21 with detection limits of 0.44 fM and 0.46 fM,respectively.In addition,this electrochemical sensing method enables detection of target microRNAs in lysates of actual MCF-7 cells（human breast cancer cells）,and therefore,it is expected to be applied to the early diagnosis of actual cancers.2.Based on gold nanoprobes（DNA/Au NPs/Thi）and duplex-specific nuclease（DSN）cleavage cycle/hybridization chain reaction（HCR）signal double amplification technology,a novel ratiometric electrochemical assay for detecting microRNA was proposed.Through the formation of the Au-N bond,the electrical signal molecule thionine（Thi）/DNA co-modified gold nanoparticles（DNA/Au NPs/Thi）were prepared.Firstly,target miRNA-141 are introduced to hybridize with ferrocene（Fc）labeled hairpin capture probes,resulting in the formation of miRNA-DNA duplexes.Meanwhile,DSN specifically cleaves the DNA in RNA-DNA duplexes,leading to the release of target and another cleaves cycle,thus numerous Fc leaves away from the electrode surface.Subsequently,the residual fragment on electrode surface acts as a HCR primer to form dsDNA polymers through in situ HCR with the presence of the primer and two probes（HDNA and HDNA’）,resulting in the capture of numerous DNA/Au NPs/Thi via DNA hybridization.As a result,the electrochemical peak currents of Thi and Fc are sharply increased and decreased,respectively.As the concentration of microRNA-141 increased,the ratio of the peak current of Thi and Fc(I_Thi/I_Fc)gradually increased.Based on this,the ultrasensitive electrochemical detection of microRNA-141 was achieved with a detection limit as low as 11 aM.The dual-signal ratio output is inherently self-calibrating for the system,which is expected to be applied to biological clinical diagnosis.3.Based on trithiocyanuric acid deposited reduced graphene oxide（TTCA/rGO）nanocomposites,a new electrochemical sensing method for the highly sensitive detection of arsenic（As（III））was constructed.Firstly,TTCA/rGO were prepared by a simple one-pot method using NaBH₄ as the reducing agent,trithiocyanuric acid and graphene oxide as raw materials.Then,TTCA/rGO was coated on the clean electrode surface to form a working electrode.In the presence of As（III）,the thiol group of TTCA/rGO modified on the working electrode can relize the preconcentration of As（III）in the solution to the working electrode surface via As（III）-S bond.The As（III）is reduced to zero valence by applying a certain voltage to the working electrode through an electrochemical workstation.Then,square wave anodic stripping voltammetry（SWASV）is used for scan test,making zero-valent arsenic on the surface of the electrode is rapidly oxidized to trivalent arsenic,and thereby generating an anodic voltammetry signal.The preparation process of the sensor is simple.Many TTCA molecules are successfully deposited on the surface of rGO throughπ-πconjugation.The reduced graphene modified on the surface of the working electrode has a large specific surface area and excellent conductivity,which can improve the electron transfer rate of the electrode surface reaction.So,the anodic stripping voltammetry signal is enhanced.With the increasing concentration of As（III）in the sample,the amount of As（III）bound to the surface of the working electrode increases,and the generated anodic stripping voltammetry peak current increases.Based on this,the sensitive and selective detection of As（III）can be realized.In addition,the sensor realizes the detection of As（III）in environmental water samples,which is of great significance in actual environmental testing.