Construction And Application Exploration Of Metal Ion Sensor Based On Signal Enhancement

Heavy metals are harmful pollutants that pose a serious threat to human and aquatic ecosystems due to their environmental persistence,toxicity and bioaccumulation.Lead ion(Pb²⁺)is one of the most toxic and persistent heavy metal ions which can cause serious harm to human health and ecosystem.Low levels of Pb²⁺can also cause a number of health problems,including neurological damage,cardiovascular damage,kidney dysfunction,reproductive dysfunction and developmental disorders.DNAzyme(DNAzyme)is a DNA molecule with similar enzyme catalytic activity screened in vitro.By Pb²⁺,DNAzyme can specifically recognize the specific cleave site of DNAzyme and make it expressed in different signal transduction ways,which has been widely used in the detection of Pb²⁺.In order to improve the detection sensitivity,signal amplification strategy plays an important role in the construction of microdetection sensors.In this paper,Pb²⁺was used to specifically identify the cleavage site of DNAzyme,and combined with the strategy of target cyclic amplification,nanomaterial amplification and DNA walker amplification,the colorimetric analysis,photoelectric chemistry technology and portable glucose meter sensing analysis mode were constructed to realize the sensitivity detection of Pb²⁺.The main contents of this experiment include:(1)The colorimetric analysis model was constructed by Fe²⁺catalyzed color-rendering combined with target circulation and Exonuclease III(Exo III)amplification strategy.Fe²⁺catalyzes the oxidation of colorless3,3',5,5'-tetramethylbenzidine(3,3',5,5'-tetramethylbenzidine(TMB)to blue ox TMB in acid solution of O₂,resulting in a color reaction.In the presence of PO₄^3-,its strong affinity for Fe²⁺precipitates free Fe²⁺ions rapidly,resulting in the loss of its color rendering ability.Alkaline phosphatase(ALP)catalyzed the hydrolysis of single base to PO₄^3-.A new free single stranded DNA(DNA₁)was generated by the hybridization of DNAzyme and s DNA by cyclic cutting of Pb²⁺microplate.Exo III specifically cleaved DNA₁ and captured DNA(c DNA)to release a single base in the hybrid double strand DNA₁,while the released c DNA continued to capture the free DNA₁hybridization to achieve the chain hybridization,cleavage and release cycle amplification strategy.Pb²⁺was determined indirectly by colorimetric method.The results show that the method has a good detection sensitivity for Pb²⁺in the linear range of 0.01-1 nmol/L,and the detection limit is up to 6.85 pmol/L.The established method can realize the determination of Pb²⁺in milk.(2)Using nanogold-functionalized polyamidoamine(Au/PAMAM)dendrimers as signal amplification materials and Cu₃(BTC)₂ and Ti O₂ as photoactive materials,a novel photochemical sensing technology was constructed to detect Pb²⁺.The Cu₃(BTC)₂/Ti O₂ functionalized FTO electrode(FTO/Cu₃(BTC)₂/Ti O₂)was used as a platform to capture s DNA.The Au/PAMAM functionalized h DNA(h DNA-Au/Pa MAM)was hybridized with s DNA through base pairing to obtain the initial photocurrent value.h DNA-Au/PAMAM detached from the electrode surface by introducing Pb²⁺specific recognition and lysis of s DNA in the hybrid chain,resulting in increased photocurrent of the sensing platform.The photocurrent increases with the increase of Pb²⁺concentration,so the quantitative determination of Pb²⁺can be realized.Under the optimized experimental conditions,the photocurrent and the logarithm of Pb²⁺concentration showed a good linear relationship in the range of 1pmol/L to 1?mol/L,and the detection limit was 0.97 pmol/L.For the first time,Cu₃(BTC)₂ was applied to the photoelectrochemical sensor detection,and a better photoelectric response was obtained,which can be used for the detection of Pb²⁺in actual water samples.(3)Based on the dual signal amplification strategy,a portable sensing mode of DNA walker signal amplification is proposed.Using Fe₃O₄ nano-magnetic beads(MB)as sensor platform,Au/PAMAM dendromolecules were prepared by means of glucose oxidase(GOx)and s DNA modification and reduction method to form s DNA/GOx/Au/PAMAM complex.Based on the base complementary pairing principle,the s DNA/GOX/Au/PAMAM complex was anchored to the capture DNA(c DNA)modified MB(MB/c DNA),and the DNAzyme could bind to the unpaired part of s DNA.In the presence of the target,Pb²⁺specifically recognized the cleavage site on s DNA and cleaved it,releasing DNAzyme and GOx/Au/PAMAM.The former continues to pair with the next s DNA of the s DNA/GOx/Au/PAMAM complex,which then initiates a new recognition,split-release,and cycle back and forward to form a DNA walker,which increases the release of GOx/Au/PAMAM to amplify the signal.Glucose(Glu)was extracted from the supernatant(GOx/Au/PAMAM)by magnetic separation,and the concentration of Glu was monitored by PGM,so as to indirectly detect the concentration of Pb²⁺.Under the optimal experimental conditions,the PGM response of the system was inversely proportional to the logarithm of Pb²⁺concentration,with a linear range of 1.00 pmol/L?1.00?mol/L and a detection limit of 0.66 pmol/L.