Preparation,Performance Regulation And Application Of Lanthanide-doped Fluoride Nanocrystal Optical Nanoprobe

In recent years,optical imaging has attracted much attention of researchers because of its advantages of non-invasive,high temporal,spatial resolution and high sensitivity.In the past decades,near infrared（NIR）window fluorescence imaging has mainly focused on near infrared region imaging window（NIR-Ⅰ,650-900 nm）.Recent studies have shown that the second near-infrared region imaging window（NIR-Ⅱ,1000-1700nm）imaging is an alternative imaging technology to NIR-Ⅰ imaging because of its ultra-deep detection depth,ultra-high temporal and spatial resolution and ultra-low photon scattering.At present,the NIR-Ⅱ optical nanoprobes mainly contain organic small molecular dyes,most semiconductor quantum dots and large-scale carbon nanotubes.However,small organic fluorescent molecules are easy to be photo-bleached when irradiated by excitation light source for a long time.Most quantum dots have high biological toxicity,wide-band emission of carbon nanotubes and low quantum efficiency.Compared with the above-mentioned probes,lanthanide-doped rare earth-based down-conversion nanocrystals have the advantages of size controllability,high quantum efficiency and good biocompatibility.Therefore,lanthanide-doped rare earth-based nanocrystals are widely used in NIR-Ⅱ in vitro/in vivo fluorescence imaging as an ideal optical probe.In addition,compared with the visible region,the advantages of near infrared band as excitation source mainly include high sensitivity,deep tissue penetration depth and high imaging sensitivity.Therefore,it is very meaningful to construct a high-performance nanoprobe for rare earth down-conversion emitted by NIR-Ⅱ.Based on this,scandium-doped lanthanide fluoride nanocrystals were first selected in this study.The optical properties of the probe in NIR-Ⅰ and NIR-Ⅱ were systematically studied,and then applied to head angiography.At the same time,we synthesized the traditional lanthanide doped NaYF₄ nanocrystals.By simple feeding,we preliminarily constructed the composite structure of rare earth silk,and further applied it to real-time monitoring of deep tissue in vivo.This paper is mainly carried out in the following three parts:（1）Yb/Er co-doped orthorhombic KSc₂F₇ nanocrystals were successfully prepared by thermal decomposition with oleic acid and octadecene as thermal solvents under argon protection.The morphology and crystal phase of the nanocrystals were characterized systematically.The optical properties of the nanocrystals were tested.The results showed that KSc₂F₇:Yb and Er nanoprobes exhibited strong 650 nm red light and 1525 nm NIR-Ⅱ emission.The nanocrystals with excellent optical properties have laid the foundation for non-invasive,high-resolution real-time optical imaging.（2）The oil-soluble rare earth nanocrystals were transformed into water-soluble nanoprobes by PAA modification and successfully applied to non-invasive high-resolution fluorescence angiography.The results showed that the main excretion pathway of nanoprobes in organisms was hepatobiliary clearance.In addition,we have used scandium-based nanoprobes to achieve non-invasive,high time,high spatial resolution imaging.Our synthesized nanoprobes are great significance for the early diagnosis of cerebral diseases.（3）Yb/Er ion-doped nanoprobes of NaYF₄ matrix were synthesized by thermal decomposition.For further application,we coated them with SiO₂.At the same time,the crystalline phase and optical properties of the nanoprobes were systematically characterized.The results showed that NaYF₄:Yb Er@SiO₂ nanoprobes exhibited strong 525 nm green light and 1525 nm NIR-Ⅱ emission.Finally,water-soluble nanocrystals were fed to silkworm,and the lanthanide-doped silk composite structure was constructed to realize real-time monitoring of deep tissues in vivo.