Fluorescence Sensing And Logic Gate Construction Based On Sulfur-Containing Quantum Dots

As a new type of fluorescent nanomaterials,Quantum Dots（QDs）have many excellent properties,such as wide source of raw materials,simple synthesis method,high fluorescence stability,and good biocompatibility.They are currently used in fluorescence sensing,bio-imaging,environmental monitoring and other fields.Quantum dots include non-metallic quantum dots,mainly carbon quantum dots and sulfur quantum dots,and metal quantum dots,mainly semiconductor quantum dots.Among them,non-metallic quantum dots have become a hot research topic in recent years because of their low toxicity and environmental friendly properties.The sulfur-containing quantum dots currently used in fluorescence sensing are mainly silver sulfide semiconductor quantum dots and sulfur-doped carbon quantum dots.This thesis focuses on the preparation of sulfur-containing quantum dots and fluorescence sensing,and incorporates the current popular logic gate operation to realize bio-computing functions.The experiment of the thesis contains the following parts.（1）Water-soluble highly fluorescent silver sulfide quantum dots（Ag₂S QDs）were prepared by microwave heating method using reduced glutathione（GSH）as the sulfur source and silver nitrate（Ag NO₃）as the silver source.The prepared Ag₂S QDs were characterized by fluorescence spectroscopy,XPS analysis,and transmission electron microscopy TEM analysis.The Ag₂S QDs showed a stable fluorescence signal at 437 nm upon excitation at 359 nm and could be quenched by Fe³⁺,and therefore could be used as a specific detection for Fe³⁺.Combining the reducing property of ascorbic acid（AA）and the oxidizing property of Fe³⁺,a dual-input IMPLICATION gate with Ag₂S QDs fluorescence as the output was constructed.（2）Sulfur-doped carbon quantum dots（GSH/L-Cy S CQDs）were synthesized by one-step microwave with L-glutathione reduced（GSH）and L-Cy S as carbon and sulfur sources.The GSH/L-Cy S CQDs was characterized by fluorescence spectra,TEM and XPS.When the S-CQDs was excited at 375 nm,a high fluorescence signal is shown at 451 nm and Co²⁺and Ni²⁺can be selectively detected in a variety of anions and cations.Combined with the metal ion masking agent citric acid（CA）for Ni²⁺,IMPLICATION gate and NOR gate logic operations can be implemented by controlling different fluorescence inputs and outputs.（3）Sulfur-doped carbon quantum dots（L-Cy S/AA CQDs）were synthesized by one-step microwave method using L-cysteine（L-Cy S）and ascorbic acid（AA）as carbon and sulfur sources.L-Cy S/AA CQDs was characterized by fluorescence spectra,TEM and XPS.When excited at395 nm,L-Cy S/AA CQDs showed a high fluorescence signal at 478 nm.Co²⁺can be selectively detected in a variety of anions and cations.Combined with metal ion chelating agent Ethylenediamine tetraacetic acid（EDTA）,PASS 0 gate can be operated by controlling different fluorescence inputs and outputs.