Research On Detection Technology Of Heavy Metals Based On Fluorescence-enhanced Quantum Dots Probes

Highly-sensitive and rapid detection of heavy metal ions in ship and marine fields is of great significance for judging mechanical failures,protecting marine environment,and safeguarding human health.Most of the existing ions detection are based on laboratory methods,which require large-scale experimental equipment such as spectrometer and complex sample preparation procedures.The whole detection process is demanding and time-consuming,which cannot meet the needs of high efficiency and low cost in actual detection.Meanwhile,some rapid detection methods generally have low sensitivity,which is difficult to meet the needs of marine heavy metal trace detection.In recent years,novel quantum dots（QDs）nanomaterials as fluorescent probes exhibit advantages of rapidity,accuracy and less sample required,showing good application prospects in the rapid detection of heavy metal ions.However,this kind of method has the problems of fluctuating fluorescence signal and weak fluorescence intensity of the probe,which limit the improvement of the sensor detection sensitivity.In view of this,four QDs probe fluorescence enhancement methods including dual emission mode,opal photonic crystal,inverse opal photonic crystal and Mn substitution are proposed in this thesis to study the highly-sensitive and rapid detection technology of Hg²⁺in seawater and Cu²⁺in lubricating oil.The main contents are as follows:（1）Aiming at the problem that the traditional single-emission probe detection mode is easily affected by external factors,which leads to the fluctuation of fluorescence signal,a new dual-emission probe is designed,which uses Cd Te quantum dots as the sensing fluorophore and Rhodamine B as the internal standard,co-assembled to achieve highly-sensitive detection of Hg²⁺in seawater.The structural characteristics and optical properties of the dual-emission probe were experimentally studied,and the fluorescence response characteristics to Hg²⁺of the dual-emission probe and Cd Te quantum dots single-emission probe were compared and analyzed.The selectivity and time effect to target ions were then studied,and the dual-emission probe was further applied to actual sample measurement to verify the practicability of this sensing effect.The results show that Cd Te quantum dots and Rhodamine B molecules are adsorbed through strong electrostatic interaction to form a dual-emission probe,and the two fluorescent materials still maintain independence luminescence.Compared with Cd Te quantum dots single-emission probe,the fluorescence intensity change of the dual-emission probe with Hg²⁺concentration shows a better linear relationship,and the detection limit was reduced to11.4 n M.At the same time,the probe has good selectivity and rapid response ability to target ions detection,and can be applied to detect Hg²⁺content in drinking water,seawater and wastewater samples.In addition,a logic gate model with Hg²⁺/glutathione（GSH）as input and fluorescence emission as output was also established.（2）In view of the problem that the probe fluorescence intensity is weak in the microfluidic fluorescent quantum dots sensing method,which limits improvement of the detection sensitivity of the sensor,a microfluidic sensor based on polymethylmethacrylate opal photonic crystals（PMMA OPCs）thin film substrate and Cs Pb Br₃ quantum dots probe was designed to achieve highly-sensitivive and rapid detection of Cu²⁺in lubricating oil.The morphology and optical properties of Cs Pb Br₃ quantum dots and the influence on the detection performance of Cu²⁺by quantum dots of different sizes were investigated experimentally.In order to improve the fluorescence intensity of in-chip probe,the PMMA OPCs film was innovatively used as the fluorescence detection substrate in the microfluidic sensor,and the fluorescence enhancement law and mechanism of photonic crystal effect on quantum dots were studied.Based on this fluorescence-enhanced microfluidic sensor,the detection performance of Cu²⁺in lubricating oil was studied.Compared with the ordinary sensor without enhanced substrate,the improvement of detection sensitivity by fluorescence enhancement effect was studied.The results show that the particle size,absorption peak and emission peak of Cs Pb Br₃ PQDs can be adjusted by changing the reaction temperature.PQDs of smaller particle size have a wider detection range for Cu²⁺,while PQDs of larger size exhibit higher detection sensitivity.PMMA OPCs can effectively enhance the fluorescence intensity of PQDs probe,and up to 26 times of fluorescence enhancement factor can be obtained when the photonic crystal band gap is coupled with the excitation light wavelength.The fluorescence enhancement effect increases the sensitivity of the sensor by 104.8%,while the detection limit is as low as 0.4 n M.In addition,the sensor has a wide detection range and good selectivity.（3）Aiming at the problem of easy collapse of PMMA OPCs in chip,a microfluidic sensor using Si O₂ inverse opal photonic crystals（IOPCs）to enhance the photoluminescence intensity of Cs Pb I₃ PQDs probe was prepared.The selective detection performance and mechanism of Cs Pb I₃ for Cu²⁺were studied firstly.Subsequently,the fluorescence enhancement of Cs Pb I₃probe was realized by using the photon stopband effect formed by the periodically arranged micro-nanostructures of IOPCs.The fluorescence enhancement performance and mechanism under different conditions were studied,and the improvement law of probe sensitivity by enhancement performance was further studied.The results show that Cs Pb I₃ can achieve good selective detection of Cu²⁺,and the fluorescence quenching of Cs Pb I₃ by Cu²⁺is due to the electron transfer from Cs Pb I₃ to Cu²⁺.The high-temperature calcined Si O₂ IOPCs can not only adhere firmly to the surface of glass substrate and improve the stability of sensor,ordered interconnected macroporous structure also facilitates the capture of detection targets.The fluorescence enhancement factor depends on the coupling degree of excitation light,emission light and photonic band gap.About 22 times of the fluorescence enhancement factor can be obtained when the coupling degree is the strongest.This enhancement effectively increases the sensor detection sensitivity by about 36.6%and reduces the detection limit to about 0.34 n M.（4）In order to enhance the fluorescence intensity of Cs Pb Cl₃ QDs and reduce lead toxicity of the probe,which realizes highly-sensitive and low toxic detection of copper ions in lubricating oil.The morphological characteristics and optical properties of Cs Pb Cl₃:Mn with different Mn doping contents,as well as the sensing behavior of QDs with a Pb-Mn molar ratio of 1:5 for Cu²⁺were experimentally studied.The detection mechanism was further explored.The results show that the average diameter of Cs Pb Cl₃:Mn particles gradually decreases with the increase of Mn doping content.The pure Cs Pb Cl₃ PQDs only have an emission peak at about 425 nm,while the emission peak appears at about 600 nm after Mn doping.The higher the Mn doping content,the greater the emission intensity of PQDs.Cs Pb Cl₃:Mn QDs were used as probe to detect Cu²⁺in lubricating oil and the experimental results show that the change of probe fluorescence intensity shows a good linear relationship with the concentration of Cu²⁺in the range of 0～1600 n M.The theoretical detection limit is 22.65 n M,and the probe exhibit strong selectivity for Cu²⁺.The fluorescence quenching was attributed to the electron transfer from Cs Pb Cl₃:Mn to Cu²⁺by analyzing the fluorescence lifetime and spectra of Cs Pb Cl₃:Mn with different Cu²⁺concentrations.