Research On Heavy Metal Ion Detection Based On Fluorescent AgInZnS Quantum Dots

Quantum Dots?QDs?have attracted great research interest in the field of optoelectronic devices,cell labeling,and sensing due to their high stability,wide absorption spectrum,strong anti-bleaching ability,and narrow emission spectrum.Especially in the field of heavy metal ion detection,it plays an increasingly important and positive role.Heavy metal pollution will cause severe harm to the environment and organisms,causing global attention and becoming a research hotspot.Fluorescent QD-based detection of heavy metal ions is a simple,fast,and specific method,and can be visually detected.By optimizing and innovating the preparation method to obtain functional QDs with good stability,high quantum yield?QY?and adjustable emission spectrum,high sensitivity and selectivity detection of heavy metal ions are realized,but there are still some inadequacies and challenges.For example,QD-based heavy metal ion sensors mainly concentrate on highly toxic QDs containing cadmium and mercury,which easily cause secondary pollution to the environment,and have low sensitivity;sensing in fluorescence quenching mode is easy to cause false positive signals,making it difficult to achieve accurate measurement of traces;lacking of reference signal and being easy to be disturbed by environmental and instrument instability reducing the accuracy of experimental results;real-time,online and highly selective detection of heavy metal ions remains a challenge.In order to solve the above problems,AgInZnS?AIZS?QDs were prepared by hot injection method and converted into aquesous ones by microemulsion method for high selectivity and sensitivity analysis of Cu²⁺in aqueous phase.To simplify the preparation process and realize the fluorescence enhancement ratio sensing of metal ions,hydrophilic AIZS QDs with good stability and high QY were prepared by one-step aqueous phase method,and the fluorescence enhancement ratio sensing performance to Cd²⁺was explored.Finally,AIZS QD coated optical fiber was designed to realize high sensitivity,selectivity and real-time detection of Cu²⁺.The main research work of this thesis is as follows:?1?The fluorescence quenching and enhanced sensing mechanisms of QD-based heavy metal ion detection are summarized,and the overseas and domestic research status is further reviewed.The shortcomings of current QD-based fluorescent metal ion sensing are analyzed,which provide theoretical basis for the hydrophilic AIZS QDs obtained through various methods to improve the sensing characteristics of heavy metal ions,and indicate the direction for future research work.?2?The Cu²⁺sensing properties of inorganic AIZS QDs were studied.The AIZS QDs were prepared by thermal injection method,and the hydrophilic AIZS–GO QDs and AIZS–DTAB QDs with good stability were obtained by microemulsion method,and applied as the fluorescence sensor for Cu²⁺in the aqueous phase.They have good specificity to Cu²⁺,and the effects of surfactants on sensing performance and mechanism were studied.?3?The AIZS/nitrogen doped Graphene QDs?NGQDs?as dual emission ratio sensor was constructed and its sensing performance to Cd²⁺were explored.The3-Mercaptopropionic acid?MPA?AIZS QDs?AIZS–MPA QDs?were directly synthesized by the aqueous phase method,and the synthesis process was optimized.The center wavelength of the optimal QDs was 550 nm and the QY was 41.2%.It was also used to detect Cd²⁺in aqueous phase.Cd²⁺can enhance the fluorescence intensity of AIZS–MPA QDs,and the enhancement mechanism is effective passivation of Cd²⁺on QDs surface defects.Finally,AIZS–MPA QDs and NGQDs were mixed in a certain ratio to construct a fluorescence-enhanced Cd²⁺ratio sensor,which achieved high sensitivity and selectivity detection.This method can effectively eliminate false positive signals,instrument fluctuations and environmental interference.?4?The performance of aqueous AIZS–SDS QD coated optical fiber sensors for Cu²⁺in aqueous phase was investigated.The oil AIZS QDs were converted into hydrophilic AIZS–SDS QDs by Sodium Dodecyl Sulfate?SDS?as a surfactant,which was stably and firmly deposited on the“Y”fiber end face under the assistance of polyvinyl alcohol,realizing high selectivity and excellent sensitivity detection of Cu²⁺in aqueous solution.The sensing mechanism of electron transfer leading to fluorescence quenching was demonstrated by absorption spectroscopy,PL spectroscopy,fluorescence lifetime,and XPS.