Construction Of DNA Molecular Logic Gate And Logic Operator Employing Electrochemical Method

In recent years,since the integration level of semiconductor materials based integrated circuit has approached its theoretic limitation,scientists are trying to develop novel computers actively.DNA computer is considered as one of the most development potential in these new-type computers.It is well known that the computer is based on logical operations.In order to establish novel DNA computer,the technology of molecular logic gate is an insurmountable path.The electrochemical method is favored due to its simple,fast,sensitive,selective and other advantages.In this thesis,a series of novel DNA molecular logic gates were proposed by using electrochemical detection technology.The characteristic DNA sequences of several common food-borne pathogens and biological small molecules were employed as detection targets.What's more,a half-adder and a half-subtracter as simple logic operators were constructed,which provides important theory support for DNA molecular logic circuits and alternative methods for nucleic acid and biological small molecule detection.(1)In chapter one,the author introduces the related concepts of molecular logic gates and logic calculators,also expounds the research progress at home and abroad.What'more the author puts forward the research contents and innovations of this round.(2)In chapter two,A "NOR" DNA molecular logic gate based on the competition-binding mode between target DNA and double-labeled probe was proposed for the detection of Salmonella(Sal)DNA and Shigella(Shi)DNA.First of all,S1 was modified on the bare gold electrode through sulfhydryl self-assembly technology.Using ferrocene(Fc)as electrochemical indicator,DP probe which labeled Fc at the two ends was settled complementarily hybridizing with S1.In the presence of targets,either Shi DNA or Sal DNA,DP would released from S1 due to the base complementary pairing and the principle of oppose surface proximity-dependent hybridization.Sal DNA and Shi DNA can be detected high selectivity and high sensitivity based on the change of electrochemical response of Fc in absence and in presence of the targets.Analysis of experimental results,the detection range of Sal DNA and Shi DNA was 1.00 nmol/L?1000.00 nmol/L and the detection limits were 0.52 nmol/L and 0.72 nmol/L(S/N=3),respectively.Furthermore,using Sal DNA and Shi DNA as inputs and the IFc as outputs,a"NOR" logic gate has been fabricated.(3)In chapter three,A " OR" DNA molecular logic gate based on the structure of Y DNA probe was proposed for the detection of Sal DNA and Escherichia coli(E.coli)DNA.Using Fc as electrochemical indicator,first of all,S1,S2 and P1 were modified on the surface of Au electrode by sulfhydryl self-assembly technology to form the structure of Y.A simple,sensitive and specific biosensor for the detection of Sal DNA and E.coli DNA was constructed based on the principle of complementary pairing and principle of a surface proximity-dependent hybridization.Analysis of experimental results,the detection range of Sal DNA and E.coli DNA was 10.00 nmol/L?1000.00 nmol/L,and the detection limit was 6.42 nmol/L and 1.58 nmol/L(S/N=3),respectively.Using Sal DNA and E.coli DNA as inputs,?I as outputs to construct "OR" logic gates.(4)In chapter four,a molecule half-adder was proposed for Listeria(List)DNA and E.coli DNA analysis based on hairpin structure.In this work,using Fc and MB as electrochemical indicator,firstly,the haripin probes S-1 and S-2 were modified on the surface of gold electrode by sulfhydryl self-assembly technology,which marked with Fc and MB,a DNA electrochemical biosensor was developed for List DNA and E.coli DNA detection simultaneously and intelligently.The loop of S-1 and S-2 were completely hybridized with List DNA and E.coli DNA,respectively.When List DNA or E.coli DNA is present,only one hairpin structure is opened,and both hairpin structures are open when both target DNAs are present.List DNA and E.coli DNA can be detect high selectivity and high sensitivity based on the change of electrochemical response of Fc and MB with and without the targets.Analysis of experimental results,the detection range of List DNA and E.coli DNA was 20.00 nmol/L?1000.00 nmol/L,and the detection limits were 1.98 nnmol/L and 8.99 nmol/L respectively.Using List DNA and E.coli DNA as inputs and the sum(??I)of ?IMB and ?IFc(??I=?IMB+?IFc)as outputs to construct a "AND" logic gate,use the ratio(Y)of ?IMB and ?IFc,(Y=?IFc/?IMB or ?IMB/?IFc)as outputs to construct a "XOR" logic gate.On this basis,a half adder with logical function was constructed.(5)In chapter five,a molecule half-subtractor was proposed for Adenosine triphosphate(ATP)and Sal DNA analysis.Using Fc and MB as electrochemical indicator,hairpin structure probe L-p and nucleic aptamers Ap were modified on the surface of gold electrode by sulfhydryl self-assembly technique,which marked with Fc and MB respectively,Ap and C-Ap were fully complementary pairing,L-p and target Sal DNA specific hybridization.When the presence of Sal DNA,the ring structure of L-P forms a rigid double-stranded;the presence of ATP can form a complexes with Ap,the C-AP was replaced,which led MB closer to the electrode surface.ATP and Sal DNA can be detected sensitively and specifically due to the current change when targets interacted with probes.Analysis of experimental results,the detection range of Sal DNA was 10.00 nmol/L?1000.00 nmol/L,and the detection limit was 2.19 nmol/L;the detection range of ATP was 10.00 nmol/L?1000.00 nmol/L and the detection limit was 3.88 nmol/L.ATP and Sal DNA were applied as inputs,?I(?I= IMB+ IFc)and the ratio(Y)of?IMB and ?IFc(Y=?IFc/?IMB or ?IMB/?IFc)as different outputs to construct "INHIBIT" and "XOR"logic gates,a new half-subtractor model for logic operation was proposed.