Preparation,Properties And Analytical Applications Of Silver Nanoclusters And Carbon Quantum Dots

Silver nanoclusters?Ag NCs?and carbon quantum dots?CDs?have excellent optical properties,low toxicity,good biocompatibility,easy preparation,high sensitivity to targets,and can also be used as an effective substitute for toxic quantum dots.In recent years,their research and application have been developed rapidly.Fluorescence method is widely used due to its simplicity,high selectivity and sensitivity,reproducibility,rapid and real-time monitoring.Based on the unique optical properties of Ag NCs and CDs,the fluorescence sensors for selective detection of single metal ions when heavy metal ions coexist and sensitive detection of p-nitrophenol were constructed in this paper.A dual readout sensor with colorimetric and ratio fluorescence was constructed by combining CDs and ZnFe₂O₄ magnetic microspheres,which was used for the detection of H₂O₂ and its related substances.Compared with single fluorescence quenching probe,ratiometric fluorescence sensing can effectively normalize the variation and obtain more accurate readouts by its self-calibration of two different emission bands.In addition,the detection mechanism of each sensor is discussed in detail.The main research contents are as follows:Part 1:Multifunctional fluorescent sensors for independent detection of multiple metal ions based on Ag nanoclustersSelective and sensitive detection of multiple metal ions is significant for biological researches and environmental monitoring,because the abnormal metal ions levels have potential damage to the human body and environment.In this study,a fluorescence sensing platform based on Ag nanoclusters has been established for independent detection of Hg²⁺,Cu²⁺,and Fe³⁺ions in a solution.The interference of the fluorescence induced by coexistent metal ions was removed by altering buffers with different pH and using different masking agents.Moreover,the detection mechanism is discussed in detail,which provides a valuable reference for the detection of heavy metal ions with metal nanomaterials.This sensor exhibits a high selectivity and sensitivity,and the linear ranges for Hg²⁺,Cu²⁺,and Fe³⁺detection were 0.05-9,0.05-18,and 0.1-18?M with the corresponding detection limits of 12,27,and 50 nM,respectively.Furthermore,this method was successfully used for analyzing the three metal ions in environmental and biological samples.Part 2:Highly selective detection of p-nitrophenol using fluorescence assay based on boron,nitrogen co-doped carbon dotsp-Nitrophenol?p-NP?contaminants seriously endanger environmental and living beings health,hence to establish a sensitive and selective method is of great importance for the determination of p-NP.In this work,boron and nitrogen co-doped carbon dots?B,N-CDs?were synthesized by one-step hydrothermal method using 3-aminophenylboronic acid as the sole precursor.The product was characterized through high-resolution transmission electron microscopy,fluorescence spectroscopy,UV-visible absorption spectroscopy,X-ray photoelectron spectroscopy,and Fourier transform infrared spectroscopy.Without any functionalized modification,B,N-CDs can be directly applied as a‘turn-off'fluorescent probe for rapid,highly selective,and sensitive detection of p-NP.The fluorescent sensor based on the B,N-CDs exhibited a broad linear response to the concentration of p-NP in the range of 0.5-60?M and 60-200?M,respectively,and provided a detection limit of0.2?M.It was found that only the absorption spectrum of p-NP has a wide overlap with the fluorescence excitation and emission spectra of B,N-CDs compared to those of other representative analogues.The response mechanism was due to the inner filter effect and the formation of dynamic covalent B-O bonds between B,N-CDs and p-NP,which endowed the sensing platform with the rapid response and high selectivity to p-NP.Finally,the sensor showed the practicability of p-NP determination in environmental water samples.Part 3:B,N-carbon dots-based ratiometric fluorescent and colorimetric dual-readout sensor for H₂O₂ and H₂O₂-involved metabolites detection using ZnFe₂O₄ magnetic microspheres as peroxidase mimicsIn this work,a two-dimensional optical sensing platform for H₂O₂,glucose,and uric acid?UA?detection is developed,which integrates the advantages of colorimetric and ratiometric fluorescent techniques.ZnFe₂O₄ magnetic microspheres with an intrinsic peroxidase-like activity are synthesized to catalyze the oxidation of o-phenylenediamine in the presence of H₂O₂,producing a typical yellow substance?oxOPD?with an absorption peak at 420 nm.The oxOPD can significantly quench the fluorescence of boron and nitrogen co-doped CDs?B,N-CDs?at 430 nm through the inner filter effect and generate a new fluorescence emission peak at 556 nm.Thus,the fluorescence intensity ratio(I₅₅₆/I₄₃₀)can be utilized for quantitative analysis of the concentrations of H₂O₂ and H₂O₂-involved metabolites?glucose and UA?.The colorimetric“naked-eye”readout based on the color change of solution can also be established to determine H₂O_2,glucose,and UA levels.The detection limit based on colorimetric sensing for H₂O_2,glucose,and UA are 0.09,0.9,and 0.9?M,respectively,and 0.1,8,and 1?M using ratiometric fluorescent sensing.Furthermore,this strategy can detect glucose and UA in human serum with satisfactory results,and provide potential applications in the detection of metabolites related to H₂O₂ release.