Controlled Synthesis Of Self-Assembled Magnetic Nanomaterials And Detection Of Trace Heavy Metal Ions

With the rapid development of industry and the improvement of living standards,the demand for the detection of trace heavy metal pollutants is increasing day by day.Lead ion(Pb²⁺)is a kind of heavy metal ion with high toxicity.Even trace amount of lead ion will seriously affect human health and quality of life.Accumulation of lead ion in the environment will cause irreversible serious impact on natural ecology.In order to meet the needs of rapid detection of trace Pb²⁺in multi-scene visualization,the preparation of visual and rapid analytical nano detection materials has become a research focus at home and abroad.However,Pb²⁺detection still has some technical bottlenecks such as low sensitivity,poor stability and complex detection steps.In this study,a new specificity detection platform of Pb²⁺was constructed by coupling nano-self-assembly technology,imprinting technology and nanozyme bionic catalysis technology,which showed detection sensitivity and stability of Pb²⁺detection and provided theoretical basis and technical support for the preparation and application of new nano-detection materials.First of all,nano-detectors are difficult to adapt to the detection needs of trace Pb²⁺in biological samples generally,due to the poor biocompatibility.In this research,urchin-like core-shell magnetic nanoparticles with spiked Ti O₂coating（Fe₃O₄@Ti O₂NPs）and core-shell magnetic nanoparticles with stable ion imprinted polymer coating（Fe₃O₄@void@IIP）were successfully synthesized.The characterization results of Fe₃O₄@Ti O₂NPs showed that it has the shell morphology of sea urchin-like spikes,which increased the biocompatibility of the material.The specific surface area ratio of the material was 52.450 m²g^-1and increased about twice specific surface area compared with Fe₃O₄.Moreover,the nanoparticles had the advantages of excellent biocompatibility and magnetism.The characterization results of Fe₃O₄@void@IIP indicated that the surface ion imprinted polymer of Fe₃O₄was successfully modified.N-H in imprinted polymers and Pb²⁺form stable metal complexes.The adsorption experiment proved that the nanoparticles had specific adsorption capacity on Pb²⁺with the highest adsorption capacity of 22.56 mg/g,which is about1.25-2.25 times of the adsorption capacity of the same type of imprinted polymer.And Fe₃O₄@void@IIP can be recycled for up to five times through superparamagnetism.Both Fe₃O₄@Ti O₂NPs and Fe₃O₄@void@IIP have good superparamagnetism and bioaffinity,which create a good foundation for the development of trace Pb²⁺detection sensors.On this basis,in order to solve the low sensitivity of the current sensitive detection of trace Pb²⁺,a fluorescence detection system for selective recognition of trace Pb²⁺was constructed by modifying the fluorescence aptamer for specific recognition of Pb²⁺at the interface of Fe₃O₄@Ti O₂NPs,which used magnetic enrichment effect to amplify the fluorescence signal.In the presence of Pb²⁺,the aptamer specifically bind to Pb²⁺,leading to separation of the fluorescent group and the quenching group.Then the recovery value of fluorescence intensity was related with the concentration of Pb²⁺in the sample.The fluorescent aptamer nanoprobes had high detection stability and accuracy(LOD=10^-10ppm,R²=0.995)and outstanding detection specificity with a linear range of 10^-10ppm to 5×10^-9ppm.It had sensitive and efficient detection performance for biological samples and showed the potential of practical application.Fluorescence detection relies on expensive instruments and is still not widely used in life scenarios.In order to develop a visual detection sensor in the field,based on the catalase-like activity of Fe₃O₄,an ion imprinted mesoporous structure was constructed on the interface of Fe₃O₄to improve the specificity of ion recognition.In the absence of Pb²⁺,Fe₃O₄@void@IIP catalase active substrate（ABTS）and the solution showed blue color.In the presence of Pb²⁺,the ion imprinted polymer at Fe₃O₄@void@IIP interface forms a stable complex with Pb²⁺,occupying the ion imprinting site,preventing mass transfer and led to weaken the activity of Fe₃O₄catalase.The higher the concentration of Pb²⁺,the lighter the color of the solution after the reaction of Fe₃O₄@void@IIP catalase activity,so the concentration of Pb²⁺was determined by measuring the absorbance of the solution.A novel detection colorimetric sensor(LOD=10^-8ppm,R²=0.97466)was developed by taking full advantage of the peroxidase-like catalytic properties of Fe₃O₄and the adsorption effect on the target ion Pb²⁺in the ion-imprinted polymer.The nanomaterials we prepared had the characteristics of ion imprinting adsorption and magnetic enrichment at the same time.The detection is sensitive,convenient and economic,providing a new idea for the construction of trace Pb²⁺real-time detection system.To sum up,in the face of sensitive detection urgent requirements for trace Pb²⁺,we prepared new trace Pb²⁺sensitive detection sensors.Fe₃O₄@Ti O₂NPs was further modification with fluorescent aptamer and then the fluorescent aptamer nanoprobe was obtained,which can accurately detect concentration of Pb²⁺in samples with high sensitivity.On this basis,in order to realize visual and rapid detection,Fe₃O₄@void@IIP was prepared based on imprinting technology and nanozyme catalytic technology,which can efficiently enrich Pb²⁺and accurately detect the concentration of Pb²⁺in the sample.The detection method is fast and economic.This material can be reused for many times,providing a research foundation for visual and qualitative detection.Due to the high biocompatibility of magnetic nanoparticles,these two new detection sensors can also be applied to the detection of Pb²⁺in real samples.They also provided technical support and theoretical basis for the construction of novel nano-detection system and provided a new idea for the construction of sensitive detection platform technology.