Detection Of Trace Metal Ions In Water Based On DNA-agncs And Graphene Oxide

Abstract:Silver nanoclusters?AgNCs?have good application prospects in fluorescence analysis due to their good light stability,easy synthesis,good water solubility,low toxicity and good biocompatibility.Based on the excellent performance,AgNCs were selected as fluorescent probes to establish a new method for fluorescence quenching detection of trace amounts of UO₂²⁺,Hg²⁺,H₂O₂ and Fe²⁺under different pH and temperature conditions.In addition,a new colorimetric method for determination of UO₂²⁺in environmental water samples was established based on UO₂²⁺enhancing the peroxidase catalytic activity of graphene oxide?GO?.In the chapter 1,the detection significance and research status of the ions to be detected are briefly reviewed.The concepts and applications of noble metal nanoclusters and graphene-based nanomaterials are also described.Furthermore,the purpose and main content of this paper are introduced.In the chapter 2,AgNCs were synthesized using hairpin DNA as template and characterized by TEM.The characterization results showed that the synthesized DNA-AgNCs were spherical and well dispersed,with an average size of 2 to 3 nm.Based on the fluorescence properties of DNA-AgNCs,we established a fluorescence detection method for UO₂²⁺and Hg²⁺.According to the static quenching between UO₂²⁺and AgNCs in NH₄Ac-HAc buffer at pH 5.0 and the dynamic quenching between Hg²⁺and AgNCs in NH₄Ac-HAc buffer at pH 7.0,the purpose of detecting UO₂²⁺and Hg²⁺under different pH conditions by fluorescence quenching method was achieved.The UO₂²⁺concentration in the range of 4.0×10^-127.5×10^-11 mol/L has a good linear relationship with the fluorescence quenching degree?F at the emission wavelength of 525 nm.The correlation coefficient r=0.996 and the limit of detection?LOD?is 1.8×10^-12 mol/L.The concentration of Hg²⁺was in a linear relationship with?F in the range of 3.0×10^-108.0×10^-9 mol/L.The correlation coefficient r=0.997and the LOD was 1.0×10^-10 mol/L.In the chapter 3,a simple and sensitive fluorescence quenching method for the detection of H₂O₂ and Fe²⁺was established base on the fact that in the presence of Fe²⁺,H₂O₂ can trigger the Fenton reaction to form hydroxyl radicals?·OH?,which can break the hairpin DNA of DNA-AgNCs into single or short oligonucleotide fragments.Since losing the protection of hairpin DNA,AgNCs were unstable and easy to form non-fluorescent silver nanoparticles with larger particle size.It was also confirmed by TEM characterization that the particle size of AgNCs increased after the addition of H₂O₂(or Fe²⁺).The concentration of H₂O₂in the range of 3.0×10^-134.5×10^-10 mol/L showed a good linear relationship with the fluorescence quenching degree?F at 525 nm,the correlation coefficient r=0.99997,the detection limit was 9.9×10^-14 mol/L.The Fe²⁺concentration showed a good linear relationship with?F in the range of 2.0×10^-76.0×10^-6 mol/L,the correlation coefficient r=0.9995,and the detection limit was 6.0×10^-8 mol/L.In the chapter 4,a simple and rapid method for visualizing quantitative detection of UO₂²⁺was established.GO has a weak peroxidase-like catalytic activity and UO₂²⁺can be adsorbed onto GO according to the strong electrostatic interaction between UO₂²⁺and negatively charged O atoms in oxygen-containing functional groups?-OH and-C=O?of GO.Based on this,we used GO to adsorb uranium to form GO-UO₂²⁺complex,which was found had the enhanced mimic enzyme catalytic activity compared with GO and can catalyze the oxidation of TMB to oxidized TMB?oxTMB?in the presence of H₂O₂ with a blue color change of the solution.Within a certain concentration range,the solution color is darker with the concentration of UO₂²⁺increasing.Based on this,the concentration of UO₂²⁺in the range of 5.90×10^-69.43×10^-4 mol/L showed a good linear relationship with the value of?A_{652 nm}.The correlation coefficient r=0.998 and the limit of detection was 4.70×10^-6mol/L.