Study On Fluorescent Nanoprobes For Analysis Of Heavy Metal Elements

In recent years,heavy metal ion pollution has become commonplace,and its separation and detection technologies have attracted much attention.Fluorescence analysis is an ideal detection method with the advantages of simple equipment,strong specificity and high sensitivity,which has been extensively used in various research fields.Fluorescent nanoprobes,such as fluorescent carbon quantum dots and noble metal nanoclusters,have prosperous application prospects due to their superior optical performance.They have been favored by researchers at home and abroad,and have become one of the research hotspots in analytical chemistry.In this dissertation,we mainly focus on the preparation of doped carbon quantum dots and gold nanoclusters with high fluorescence quantum yield,strong optical stability,and good biocompatibility to obtain fluorescent nanomaterials with excellent optical properties.A series of characterization techniques were performed corresponding characterizations to reveal the interaction mechanisms between the probe and target analytes,thereby further applying it to the analysis and detection of metal ions.The main research contents of this thesis are summarized as follows:Chapter 1 Polyacrylamide-based nitrogen-doped carbon quantum dots as fluorescence nanoprobes for high sensitive and selective determination of mercury?II?High fluorescence nitrogen-doped carbon quantum dots?N-CQDs?were simply synthesized via a one-step hydrothermal method with polyacrylamide,which simultaneously applied as carbon and nitrogen sources.The diameter,crystal shape,morphology,ultimate composition and optical performance of the synthesized N-CQDs were characterized by transmission electron microscopy?TEM?,X-Ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FT-IR?,ultraviolet-visible spectrophotometer?UV-Vis?,and fluorescence spectrophotometer?FS?,respectively.The obtained results showed that the particle size distribution of N-CQDs was uniform,and the surface was rich in functional groups such as carboxyl,carbonyl,and amide groups.In addition,the synthesized N-CQDs were proved to be fluorescent nanoprobes for mercury ion detection with excitation-dependent and excellent stability in acidic and alkaline media which could adapt to various sophisticated pH environments.According to the mechanism of photoinduced electron transfer,N-CQDs can be used as fluorescent nanoprobes for mercury ion detection.Under optimal experimental conditions,the nanoprobe showed a good and sensitive linear response?R²=0.9988?toward mercury?II?within the concentration range of 0.25⁵0?M with a low detection limit of 30 nM.The method has been successfully applied to the analysis of mercury?II?in environmental water samples.Quantitative recoveries were achieved within the range of 94.0¹02.8%,and the relative standard deviation is 0.97³.19%.These satisfactory results suggested that this novel nanoprobe had prosperous development and application prospects for analysis of mercury?II?in environmental water samples.Chapter 2 Nitrogen-doped carbon quantum dots with Dendrobium candidum as carbon sources for high sensitive and selective determination of chromium???A novel nitrogen-doped fluorescent carbon dots was successfully prepared via a simple one-step hydrothermal method using the medicinal plant Dendrobium candidum as an environment-friendly carbon-containing precursor for the first time and ethylenediamine as nitrogen sources.The diameter,morphology,ultimate composition and optical performance of the prepared Dendrobium-based N-CQDs were characterized by a series of analytical characterization techniques,respectively.The photostability was also investigated by investigating the conditions of ionic strength,pH,and storage time.The obtained results showed that the particle size distribution of Dendrobium-based N-CQDs was uniform with the fluorescence quantum yield as high as 27.6%,and it also exhibited good excitation dependence and excellent light stability.Based on the fluorescence quecnching mechanism of fluorescent inner filter effect,it has high sensitivity,selectivity and anti-interference ability for chromium?VI?.Under optimal working conditions,the nanoprobe showed a good and sensitive linear response?R²=0.9988?toward chromium?VI?within the concentration range of 0.1⁵0?M with a low detection limit of 22 nM.This method has been successfully applied to the detection of chromium?VI?in environmental water samples and soil samples,providing a new idea for the development of green natural compound carbon materials.Chapter 3 Milk protein-protected gold nanoclusters-based ratiometric fluorescence nanoprobes for visualization and ratiometric detection of copper?II?In this study,gold nanoclusters with excellent optical properties were successfully synthesized by one-step chemical reduction with milk protein as surface reducing agents and stabilizers.The particle size,morphology,ultimate composition and optical performance of the water-soluble MP-AuNCs were characterized by transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,Fourier transform infrared spectroscopy?FT-IR?,ultraviolet-visible spectrophotometer?UV-Vis?,and fluorescence spectrophotometer?FS?,respectively.The results showed that the MP-AuNCs had uniform particle size distribution and emitted red fluorescence under the 365 nm UV lamp with strong light stability.Based on the fluorescence recovery effect of copper?II?on MP-AuNCs/tetracycline complex system,a near-infrared dual-emission ratiometric fluorescent nanoprobe mediated by tetracycline was established for visualization and ratiometric detection of Cu²⁺.Under optimal working conditions,the sensor showed a good and sensitive linear response?R²=0.9955?toward copper?II?in the concentration range of 0.15³0?M with a low detection limit of 10 nM.The method has been successfully applied to the detection of copper?II?in human urine samples and blood samples with potential application value and broad development,which provides an important theoretical basis for the construction of novel fluorescent nanoprobes.