Interfacial Synthesis For Ag₂S/ZnS Core/Shell Quantum Dots In A Droplet Microreactor

In recent years,near-infrared quantum dots(QDs)have received widespread attention in the fields of in-vivo imaging,diagnosis,and photothermal therapy due to deep tissue imaging and low autofluorescence in the near-infrared window.Silver chalcogenide QDs are suitable for imaging in the NIR-?window due to their narrow band gap.Because it does not contain Cd,Hg,Pb and other poisonous elements,and it has a very low solubility product constant,so it has good biocompatibility.However,the quantum yield of silver chalcogenide QDs is far inferior to that of Cd Se,Pb S and other QDs,which seriously limits its development.Studies show that coating the ZnS shell can effectively improve the fluorescence performance of the QDs,and the thickness of the shell has an important effect on the fluorescence of the QDs.At present,due to the large lattice mismatch,there are fewer methods for silver-sulfur QDs to coat a shell.So far,there are two main strategies for the growth of the shell on silver chalcogenide QDs,including alternating ion layer adsorption and microwave synthesis.The alternating ion layer adsorption method can effectively prevent the shell precursors from nucleating alone,but the operation is complicated and it is difficult to precisely control the shell thickness.For microwave synthesis method,the particle size of core/shell QDs was usually larger than 20 nm,with a wide diameter distribution and poor monodispersity.Droplets microreactor as a favorable platform for controlled synthesis has the advantages of fast mass and heat transfer,low reagent consumption,good repeatability,and accessibly control of reaction conditions.In combination with other equipment,the reaction process can be monitored.In addition,the large specific surface area of the droplet is more conducive to the interface reaction,and the adsorption of nanoparticles at the interface and the internal and external fluid circulation of the droplet make the reaction at the interface faster.Based on this,the works of this article are as follows:(1)Ag₂S/ZnS core-shell quantum dots were prepared in a droplet microreactor by interfacial synthesis.At the same time,the thickness of the shell was adjusted,and the effect of different shell thicknesses on its fluorescence properties was studied.The dispersed phase was an aqueous solution of Ag₂S,and the oil phase was a solution of mineral oil containing a Zn(Ac)₂-OAm precursor.Stable droplets were formed at the flow focusing port.The Ag₂S/ZnS core-shells QDs were continuously and rapidly synthesized at room temperature.By adjusting the concentration of Zn(Ac)₂-OAm precursor and Na₂S solution,the shell growth of Ag₂S/ZnS core-shell QDs was regulated,and Ag₂S/ZnS QDs with different shell thicknesses(0-2.58 layers)were obtained.The effect of the thickness of the shell layer on the fluorescence performance of the quantum dots was studied,and the optimal shell thickness of the Ag₂S quantum dots was explored.(2)Using a combination of a microfluidic platform,a fluorescence inversion microscope,and a fiber optic spectrometer,the on-line acquisition parameters were optimized to realize the online monitoring of synthesis process for the Ag₂S/ZnS core-shell QDs.The extinction coefficient was measured,and the relationship between fluorescence intensity and the QDs particle concentration in the chip was studied.On this basis,the reaction process was studied,and the dynamics of the water phase transfer process was explored.