Study On The Detecion Of Heavy Metal Ions Based On Nanocomposites Materials Of Electrochemical Aptasensors

The heavy metal ion pollution has always been a major problem in environmental pollution and food safety.Some heavy metal ions can be enriched in the human body through the food chain and are difficult to degrade in the environment.Most of them exist in the form of complexes,which can inhibit the activity of enzymes in the body and seriously affect the human healthy.Therefore,the development of a method for detecting heavy metal ions have important research value.Compared with traditional methods,electrochemical analysis method have the advantages of time-saving,high sensitivity and easy operation.In addition,the use of nucleic acid aptamers as the original biometrics has strong specificity for the target.At present,the combination of nucleic acid aptamer technology and electrochemical analysis method to construct electrochemical aptasensors is widely used in the analysis and determination of heavy metal ions.This article mainly considers improving the conductivity of the electrode surface and the sensitivity of the sensor itself.Three functionalized nanocomposites and different DNA signal amplification strategies were used to detect Hg²⁺and Pb²⁺.The contents of the three specific electrochemical aptasensors we constructed to detect Hg²⁺and Pb²⁺are as follows:1.First,use water bath synthesis method to prepare graphene oxide（GO）and ascorbic acid reduction method to prepare silver platinum nanoparticles（Ag Pt）,and construct Ag Pt/GO functional nanocomposite by physical adsorption to modify electrode surface to enhance conductivity,exonuclease（Exo III）which can digest single nucleotide and release single strand to form a cycle,resulting in improvement of the sensitivity of the sensor.Thus,the purpose of amplification can be realized,and[Fe（CN）₆]^3-/4-were used as a signal probe to construct a label-free sensor for the detection of Pb²⁺.In the presence of Pb²⁺,it can combine with the aptamer strand（Apt）rich in G bases to form a G-quadruplex structure,and the released complementary strand（S₁）can be complementary to the capture probe（CP）on the electrode surface.The presence of Exo III triggers the function of digesting the 3′-end nucleotide and the release of S₁ which acts on the next CP.Finally,a large number of short-chain capture probes are produced on the electrode surface,which is recorded by DPV response of[Fe（CN）₆]^3-/4-.The results showed that the electrical signal of the sensor showed a good linear relationship in the range of Pb²⁺concentration from 0.05 p M to 5 n M,the detection limit was 0.019 p M,and the recovery rate of standard tap water was 96.0-108.4%.2.In order to overcome the problem of high background peak current caused by the non-labeled sensor in the previous chapter,this chapter adopts the copper-based metal organic framework@platinum-palladium nano-particles（Cu-MOFs@Pt Pd NPs）as the signal probe to construct the labeled sensor for Hg²⁺Testing research.Preparation of polydiallyldimethylammonium chloride-graphene（PDDA-Gr）by hydrazine hydrate reduction method and gold seed growth method to prepare gold nanorods（Au NRs）,and PDDA-Gr/Au NRs functionalized nanocomposites were synthesized by electrostatic adsorption,which are used to modify the electrode surface to enhance conductivity.Mg²⁺-dependent DNAzyme is used to drive the DNA Walker cycle and Cu-MOFs@Pt Pd NPs increase the electron transmission rate.The double-amplification signal strategy improves the sensitivity of the sensor.When Hg²⁺is present,it can trigger the opening of the hairpin chain HP on the electrode surface to form a T-Hg²⁺-T mismatch structure with some bases of S2,and the presence of Mg²⁺can cause DNAzyme to specifically cut Cu-MOFs@Pt Pd NPs/S1contains r A,and the DNA Walker cycle can continuously cause the signal label to be cut.The signal reduction degree of Cu-MOFs@Pt Pd NPs is recorded by signal response of SWV.The results showed that the electrical signal of the sensor showed a good linear relationship in the range of Hg²⁺concentration from 0.001 to 100 n M,the detection limit was 0.52 p M,and the recovery rate of spiked milk powder was between 92.6-107.4%.3.Based on the detection of single ions in the previous two chapters,considering that the sample solution contains more than one metal ion,this chapter develops a new type of electrochemical sensor for simultaneous detection of Hg²⁺and Pb²⁺.The oil bath method was used to prepare polyethyleneimine-reduced graphene oxide（PEI-r GO）and citric acid reduction method to prepare gold nanoflowers（Au NFs）,and the functionalization of PEI-r GO/Au NFs nanocomposite materials was constructed by chemical bonding（Au-N）,which are used to modify the electrode surface to enhance conductivity.Exo III’s internal loop amplification and cerium-based metal organic framework@platinum-palladium nano-particles（Ce-MOFs@Pt Pd NPs）catalyze ascorbic acid（AA）two amplification strategies respectively,which enables control of two kinds of signal.When Hg²⁺and Pb²⁺are present at the same time,the mismatch complementation of T-Hg²⁺-T is still formed so that Exo III digests the3′-end nucleotide with methylene blue（MB）,and the presence of Pb²⁺makes the corresponding DNAzyme specific cut The r A part of the substrate chain finally captures Ce-MOFs@Pt Pd NPs/S₃ and the remaining part of the base complementary,and records the signal reduction degree of MB and the signal enhancement degree of Ce-MOFs@Pt Pd NPs catalyzed by AA by means of SWV.The results show that the electrical signal of the sensor exhibits a good linear relationship in the range of Hg²⁺and Pb²⁺concentrations from 0.001 to100 n M,the detection limits are 0.11 p M and 0.093 p M,and the recovery rate of standard tap water is between 92.6-107.4%.