Preparation And Optical Properties Regulation Of Upconversion Nanoparticles And Its Application On Photodegradation Of Amyloid Aggregates

The upconverting material is a material that has an anti-Stockes effect,emits visible light after absorbing near-infrared light and developed rapidly in many fields due to their sharp emission peaks,excellent luminescence stability and chemical stability,large Stokes shifts and low biotoxicity.Especially in the field of biomedicine,upconversion materials has extremely extensive applications,such as medical imaging,photodynamic therapy and biomolecular detection,particularly in the treatment of Alzheimer’s disease（AD）which has attracted wide attention.In this paper,a series of experiments have been carried out through rare earth element yttrium（Yb）and yttrium（Er）co-doped upconversion nanoparticles（UCNPs）—β-NaYF₄:Yb/Er prepared by thermal solvent method.The main research contents and results are as follows:1.Firstly,the effects of the doping concentration of Yb³⁺on the morphology,particle size and upconversion luminescence properties ofβ-NaYF₄:Yb/Er were investigated.Subsequently,the effects of external factors such as laser power,self concentration,acid（hydrochloric acid）and alkali（sodium hydroxide）on the fluorescence luminescence properties ofβ-NaYF₄:Yb/Er were studied.The results showed that the morphology ofβ-NaYF₄:Yb/Er changed from circular to hexagonal with the increase of Yb³⁺doping concentration;When the concentration of Yb³⁺increased from 8%to 98%,the particle size increased from 42.5±8.6 nm to 402.4±31.0 nm.β-NaYF₄:Yb/Er had the best upconversion luminescence property when the Yb³⁺doping concentration was 18%.The results of external factors indicated dependence of the up-conversion fluorescence ofβ-NaYF₄:Yb/Er on power and concentration.In addition,hydrochloric acid had quenching effects on the fluorescence intensity ofβ-NaYF₄:Yb/Er,while sodium hydroxide had certain fluorescence intensity enhancement effects.2.Amyloid aggregates that cause the pathogenic core of Alzheimer’s disease（AD）was removed by photodynamic therapy.First of all,β-NaYF₄:Yb/Er was prepared by thermal solvent method,followed by silica coating modification on the surface and amination treatment on the SiO₂ layer.And than,the surface amino group was covalently bonded to the photosensitizer rose bengal（RB）using an EDC/NHS coupling agent to form a stable composite.Finally,the degradation of amyloid fibrils was carried out under the irradiation of980 nm near-infrared laser.The results showed thatβ-NaYF₄:Yb/Er@SiO₂@RB can produce reactive oxygen species（singlet oxygen）and effectively eliminate amyloid aggregates at a concentration of 100μg/mL under the irradiation of 980 nm near infrared laser.Therefore,the rational use of upconversion nanotechnology will be an effective method to treat AD in the future.3.Upconversion fluorescence luminescence intensity ofβ-NaYF₄:Yb/Er was enhanced by doping metal ions(Li⁺,Co²⁺and Cu²⁺),which ROS can be more effectively generated,and the amyloid aggregates can be more effectively degraded.The photoresponse effect between2D materials（GO,MOS₂,g-C₃N₄ and BN）and fluorescence intensity ofβ-NaYF₄:Yb/Er was investigated.The results showed that Li⁺,Co²⁺and Cu²⁺can replace some ions or occupy the void position to change the local crystal field,thereby increasing the fluorescence emission intensity.Among the three metal ions,Li⁺doping had best enhancement effect on fluorescence intensity ofβ-NaYF₄:Yb/Er.When the Li⁺doping concentration was 10 mol%,the fluorescence intensity was increased by 4.17 times;The particle size ofβ-NaYF₄:Yb/Er doped with Co²⁺decreased to a certain extent.When the concentration of Co²⁺was 2 mol%,the fluorescence intensity increased by 2.68 times.The morphology,particle size and crystal structure ofβ-NaYF₄:Yb/Er doped with Cu²⁺were changed.When the concentration of Cu²⁺was 5 mol%,the fluorescence intensity increased by 2.15 times.In addition,partial 2D material can effectively respond toβ-NaYF₄:Yb/Er and the resulting photoresponse was different.GO and MoS₂ had quenching effects and g-C₃N₄ had enhanced effects while BN had no significant effect on the fluorescence intensity ofβ-NaYF₄:Yb/Er.Therefore,only 2D materials with high carrier mobility and other properties can produce photoresponse toβ-NaYF₄:Yb/Er.Functional upconversion nanoparticles can produce ROS more effectively,which makes the degradation of amyloid aggregates more effectively after fluorescence enhancement.