Electrochemical Biosensor For Analysis Of Mercury Ion?DNA And MicroRNA Based On The Guanine Nanowire Amplification

DNA electrochemical biosensor is a new technology based on the electrochemical detection.In recent years,with the rapid development of science and technology,DNA electrochemical biosensor is a new cross discipline which relates to the field of biochemistry,medicine,electrochemistry and information technology.Thus,DNA electrochemical biosensor has been widely used in the fields of genetic diagnosis,judicial expertise,environmental monitoring and food hygiene.DNA electrochemical biosensor integrates a nucleic acid as the biological recognition element,and has specific affinity capacity of biomolecule and the ability of specific recognition to target,which have achieved highly sensitivity and selectivity for the analysis and detection of target.Combining the high specificity of nucleic acid probes and the excellent sensitivity of electrochemical detection techniques,DNA electrochemical biosensor has become the most important branch of biosensors,and has the advantages of simple,rapid,low cost and sensitive.In addition,utilizing signal amplification technology,it is particular attractive to construct the DNA electrochemical biosensor with high sensitivity and selectivity.In this paper,we developed three kinds of DNA electrochemical biosensors for sensitive and selective detection of mercury ion,DNA and micro RNA based on the direct growth of guanine nanowire.The main work is as follows:Part 1 A label-free electrochemical sensor for detection of mercury?II?ions based on the direct growth of guanine nanowireIn this work,we develop a DNA electrochemical sensor for the sensitive detection of Hg²⁺ based on the guanine nanowire amplification.Initially,the A1 probe,which contains the thiol group,stabilized on the dithiothreitol?DTT?monolayer modified gold electrode.In the presence of Hg²⁺,the A1 probe,a T-rich oligonucleotide,could hybridize with the A2 which contain T bases at the 5' terminus via T-Hg²⁺-T base pairs in DNA duplexes.Then,A2 can partially hybridize with A3 at the 5' terminus to form the sandwich structure.The c-myc region from A3 at its 3' terminus is G-rich sequences,and can form a parallel G-quadruplex structure with the help of K+.With c-myc,the parallel G-quadruplex could trigger the formation of guanine nanowire in the presence of Mg²⁺.Then,with the help of hemin,the hemin/G-quadruplex repeat units formed,and a great increased current signal was obtained.This proposed electrochemical DNA biosensor allows a reliable Hg²⁺detection with a detection range from 100 pmol L^-1to100 nmol L^-1 and a low detection limit down to 33 pmol L^-1.In addition,this special design has excellent analytic performance for Hg²⁺ detection,and it has been successfully applied to detect Hg²⁺in water samples.Part 2 Sensitive detection of HIV DNA by coupling exonuclease III-assisted target recycling and guanine nanowire amplificationIn this paper,we develop a strategy with the combination of exonuclease III?Exo III?-assisted target recycling and guanine nanowire amplification for the sensitive detection of HIV DNA.First,the HP2 probe,which contains a thiol group,stabilized on the dithiothreitol?DTT?monolayer modified gold electrode.In the presence of target DNA,it can hybridize with the 3'-protruding terminus of HP1 to form a stem with blunt terminus,which can be cleaved by Exo III to release a digestion?help DNA?and target DNA for target recycing.Then,the released help DNA could hybridize with the capture probe?HP2?,and c-myc region was opened.With the help of K+,the G-rich sequences can form the parallel G-quadruplex.After the addition of c-myc,the G-quadruplex could trigger the formation of guanine nanowire on electrode surface in the presence of Mg²⁺.In the presence of hemin,the hemin/G-quadruplex repeat units formed,and a current signal was obtained.Besides,the DNA biosensor is simple,high sensitive,high selective and has good reproducibility.It has been successfully applied to detect the target in serum samples.Part 3 Amperometric biosensor for mi RNA based on the use of tetrahedral DNA nanostructure probes and guanine nanowire amplificationIn this work,we have developed a novel electrochemical biosensor for the successful detection of target mi RNA-21 based on tetrahedral DNA nanostructure as the recognition probe,coupled with guanine nanowire amplification.The tetrahedral DNA structure is designed by three thiolated nucleotide sequences and a longer single-stranded DNA?ss DNA?,and the tetrahedral DNA structure self-assembles by four nucleotide sequences with one step of the thermal denaturation.In our design,the DNA tetrahedral DNA nanostructure was modified on gold electrode surface via Au-S bonds.In the presence of micro RNA,the pendant hairpin of the tetrahedral structure was opened.Then,the released stem,which consisted of c-myc sequence at 3' termini,could form a parallel G-quadruplex structure with the help of K+.In the presence of c-myc,the parallel G-quadruplex could induce the formation of guanine nanowire on the electrode surface with the help of Mg²⁺.After the addition of hemin,the hemin/G-quadruplex repeat units could show an increased current signal.The proposed biosensor based on this strategy is simple,label-free,high sensitive and sensitive.This special design allows a reliable micro RNA detection with a detection range from 500 fmol L^-1to 10 nmol L^-1and a low detection limit down to 176 fmol L^-1.In addition,this biosensor can be applied successfully in serum samples analysis.