Construction Of Fluorescence Probe System Based On Sulfur Quantum Dots And Its Application In Analysis And Detection

Objectives:In order to realize the successful application of SQDs in practical detection,this thesis is proposed to establish a new fluorescence detection method based on sulfur quantum dots（SQDs）for the detection of copper ion(Cu²⁺)content in Paris polyphylla var.yunnanensis,lead ion(Pb²⁺)and enrofloxacin（ENR）content in river water samples,and lomefloxacin（LOM）content in milk samples.Methods:1.The synthesized SQDs were characterized by transmission electron microscopy,X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.Their optical properties were investigated by fluorescence spectrophotometer and ultraviolet-visible spectrophotometer.2.Based on the fluorescence quenching effect between SQDs and Cu²⁺,a new method for fluorescence detection was established using SQDs as a fluorescent probe.The stability of this fluorescent probe,the optimal conditions in Cu²⁺detection,and the accuracy and sensitivity of the established method were investigated to detect Cu²⁺content in Paris polyphylla var.yunnanensis.3.Based on the static quenching effect between SQDs and Pb²⁺and the recovery of fluorescence after the addition of ENR,a fluorescence“off-on”sensing platform for detecting Pb²⁺and ENR based on SQDs was established using SQDs as a fluorescence“off-on”probe.The optimal conditions,accuracy,and sensitivity of Pb²⁺and ENR detection were studied to achieve the detection of Pb²⁺and ENR in actual river water samples.4.Using SQDs as the fluorescence reference signal and carbon quantum dots（CQDs）as the fluorescence response signal,the SQDs-CQDs ratiometric fluorescence probe was composed.The concentration of SQDs and CQDs,the optimal pH value and response time for detection,and the volume ratio of SQDs-CQDs were investigated.Based on the fact that LOM can be quenching the yellow fluorescence of CQDs without affecting the blue fluorescence of SQDs,and that the color of SQDs-CQDs solution changes from yellow to blue with increasing LOM concentration,a fluorescence and colorimetric sensing platform of LOM was constructed to detect LOM in milk samples.Results:1.The synthesized SQDs had good dispersion in a solvent,with uniform subspherical morphology and an average particle size distribution between 4.4-7.5 nm,with abundant sulfur atoms and sulfonic acid groups on the surface.2.The optimum pH value for detecting Cu²⁺was 7 and the optimum response time was 5min.The established method had a linear range of 20-200μM,a limit of detection（LOD）of6.78μM,high selectivity in the presence of other ions,spiked recoveries in the range of 92%-109%and relative standard deviation（RSD）in the range of 1.2%-3.7%.3.The optimal pH values for Pb²⁺and ENR detection were 7,and the response times were5 min and 20 min,respectively.The linear ranges of the method for Pb²⁺and ENR detection were 20-250μM and 100-600μM,with LOD of 1.90μM and 4.69μM,respectively.The spiked recoveries were 101%-109%and 93%-108%,respectively,with RSD of 0.8%-3.5%and 0.9%-2.7%.4.Under the optimal experimental conditions,the concentrations of SQDs and CQDs were20 mg/m L and 1 mg/m L,respectively,whereas the volume ratio of SQDs to CQDs was 1:2.The relative fluorescence intensity and absorbance of SQDs-CQDs ratiometric fluorescence probes had an excellent linear relationship in concentration ranges of 50-700μM and 10-200μM for LOD with a limit of detection of 3.11μM and 1.92μM,respectively.Conclusions:1.SQDs were successfully synthesized in this thesis.2.The new fluorescence detection method of SQDs can be successfully applied to detect Cu²⁺content in Paris polyphylla var.yunnanensis with satisfactory results.3.The“off-on”fluorescence sensing platform based on SQDs could be used to detect Pb²⁺and ENR in actual river water samples.4.A ratiometric fluorescence was formed by the combination of SQDs and CQDs.At the same time,a new fluorescence-colorimetric detection method was successfully established to detect LOM in milk samples.