Preparation And Characterization Of Acid-responsive Aggregated Near-infrared Ag₂S Quantum Dots

In recent years,as a new type of near-infrared quantum dots with low toxicity,Ag₂S quantum dots have attracted the attention of nanotechnology workers.Compared with visible light quantum dots,the near-infrared fluorescence emitted by near-infrared Ag₂S quantum dots has biological properties.It has the advantages of deeper tissue penetration,less interference from the biological environment,and lower imaging background.At the same time,the near-infrared Ag₂S quantum dots also have good photoacoustic performance and photothermal conversion effect due to their absorption in the near-infrared region.Therefore,near-infrared Ag₂S quantum dots are an ideal nano-therapeutic agent integrating near-infrared fluorescence imaging,photoacoustic imaging and photothermal therapy,which have great potential in the field of cancer diagnosis and treatment.Studies have shown that in order to achieve long-term blood circulation and deep penetration of tumor tissue,the hydrated particle size of near-infrared Ag₂S quantum dots should generally be about 50 nm.However,nanometerials with a small particle size are easy to flow back into blood or transfer to surrounding norm mal,tissues after reaching tumor tissues that causes the enrichment of nanometerials have greatly reduced in tumor suite.Therefore,it is a key scientific issue to improve tumor imaging and treatment performance that how to achieve efficient enrichment of near infrared Ag₂S quantum dots in tumor tissues.In this paper,the surface structure of near-infrared Ag₂S quantum dots is scientifically designed to enable responsive aggregation in a simulated tumor slightly acidic environment in vitro,so as to achieve efficient enrichment of near-infrared Ag₂S quantum dots in tumor tissue.The synthesized Ag₂S@PNH-CDM-PEG quantum dots will break the amide bond between the acid-sensitive molecule 2-propionyl chloride-3-methylmaleic anhydride（CDM）and PEG under acidic conditions,and the hydrophilic PEG will be dehydrated.In order to reduce the hydrophilicity of the Ag₂S quantum dot nanocomposite agent,its LCST temperature is lower than the physiological temperature of 37℃,and the PNH thermosensitive polymer rapidly changes from a dissolved state to a collapsed state,which promotes the in situ aggregation of Ag₂S quantum dots.Based on this,the preparation and properties of acid-responsive aggregated near-infrared Ag₂S quantum dots were studied in this thesis,that focus on near-infrared Ag₂S quantum dots.The main research contents are as follows:（1）Preparation of acid-responsive aggregated near-infrared Ag₂S quantum dots.The preparation of near-infrared Ag₂S quantum dots adopts the classical high-temperature organic phase synthesis method,and the quantum dots are examined by the morphology,crystal phase,size and monodispersity of the quantum dots.The experimental data show that the diameter of the near-infrared Ag₂S quantum dots prepared by this method is about 3.7±0.4 nm,the fluorescence emission peak position is at 1100 nm in the near-infrared region,and the fluorescence performance is excellent.The particles have good dispersibility in organic solvents,and the fluorescence quantum yield is as high as 9%.Then,the temperature-sensitive polymer PNH was used as modifier,and the Ag₂S quantum dots were water-soluble modified by the method of hydrophobic coating,and the near-infrared Ag₂S@PNH quantum dots with LCST temperature characteristics were prepared.The Ag₂S quantum dots are basically the same,at 1100 nm,and the fluorescence quantum yield is 6%.At the same time,the photothermal properties of Ag₂S@PNH quantum dots were investigated.The experiments showed that when the concentration of quantum dots was 300 ppm,the solution temperature increased by 50℃,and the photothermal properties were superior.Under cycling,the photothermal properties of quantum dots still maintain good responsiveness.Finally,Ag₂S@PNH-CDM-PEG quantum dots,namely acid-responsive aggregated near-infrared Ag₂S quantum dots,were prepared by further coupling CDM and NH₂-PEG.（2）Study on the relationship between the surface structure of acid-responsive aggregated near-infrared Ag₂S quantum dots and their responsive aggregation properties.The experimental results show that when the molar mass ratio of NIPAAm and HEAm is 85:15,the synthesized PNH polymer has the best structural properties,and at 37℃,the acid-responsive aggregated near-infrared Ag₂S quantum dots can be guaranteed to be weak at p H 7.4.It has good dispersibility under alkaline conditions,while in the weakly acidic environment of p H 6.5,rapid responsive aggregation can occur and good optical properties can be maintained.The performance research results before and after acid-responsive aggregation show that the photothermal conversion efficiency of Ag₂S quantum dots in the dispersion system is 30.5%,and the photothermal conversion efficiency of Ag₂S quantum dots in the aggregation system is 41.3%.Obviously,the latter is better than the former.The results of the biosafety investigation show that in the p H 7.4 and 6.5 environments,when coexisting with acid-responsive aggregated near-infrared Ag₂S quantum dots,the MTT experiment results show that the cell survival rate is over 90%,and the biosafety is good.Cell phototoxicity experiments showed that He La cells were incubated with 300μg·m L-1 of Ag₂S@PNH-CDM-PEG solution for 12 h,and irradiated with 808 nm laser for 5 min,the cell survival rate was only 40%,and the photothermal treatment performance was superior,which is a good choice for the follow-up treatment.Applied research in the field of biomedicine has laid a good foundation.