Research And Application Of Hydrophilic Rare Earth Hydroxide Nanosheets As Fluorescence Probes And Multifunctional Magnetic Resonance Imaging

Layered rare-earth hydroxides（LRHs）nanosheets,which combine the unique optical properties and magnetism benefits of rare earth elements with the structures of ultrathin 2D nanosheet with high surface-to-volume ratios,anisotropic physical and flexible bioactivity.It has great application prospect in the fields of fluorescence detection,drug delivery,biosensors and biomedical imaging.However,when these nanosheets are applied in water environment,they still face some problems urgent to be solved,such as agglomeration,poor stability,thick nanosheets and poor hydrophilicity.Therefore,this paper focuses on the preparation of hydrophilic LRH nanosheets and the study of fluorescence and MRI ability,mainly including the following aspects:1.The Htta-modified Ag NPs-loaded Eu/Y hydroxide nanosheets（LA-Ag@Eu/Y@tta）were prepared to detect of Pb²⁺as a"turn-on"fluorescence probe.Because of the local surface plasmon resonance（LSPR）effect,the Ag NPs loaded on the nanosheets not only effectively ameliorate the fluorescence performance of the nanosheets at water,but also increase the detection sensitivity to Pb²⁺ions.Combining the lumincsence excitation spectra,emission spectra,fluorescence lifetime analysis and infrared spectrum,the mechanism of the enhanced fluorescence response of LA-Ag@Eu/Y@tta to Pb²⁺ions was systematically discussed.2.The Eu³⁺doped yttrium hydroxide monolayer nanosheets with high stability,good dispersion and the size on micron level were synthesized by ultrasonic processing in ultrasound cell disruptor with PAA as stabilizer,which had good fluorescence response to temperature and linear.When the temperature increases,the back energy transfer processes from Eu³⁺to tta^-may occur to quench the fluorescence.In addition,the energy difference of Eu³⁺（⁵D₀→⁷F₂）is well-matched with the vibration frequency of hydroxyl（O-H）.Their effective vibration matching frequencies significant promote the decrease of Eu³⁺radiative transition probabilities,resulting in fluorescence quenching at 612 nm with the rising of temperature.The Eu³⁺doped monolayer nanosheets with large specific surface area and rich surface hydroxyl（O-H）are more sensitive to chemical environment,and have high application value in the field of temperature detection.3.MRI contrast agents have been used to enhance the contrast to sense the pathological differences between background tissue and regions of diagnostic interest,which is widely applied in clinical.The Gd/Y hydroxide monolayer nanosheets with sizes of～100 nm,good dispersion and stability in aqueous solution have been prepared,showed superhigh T₁/T₂ relaxation performance and low cytotoxicity.The nanosheets with different Gd/Y ratios were investigated to reduce the dosage of Gd³⁺.Different from the pure Gd-based MRI contrast agent reported in the literature,the 10%-Gd-doped nanosheets were found to exhibit the highest relaxivity at 3T(r₁=103.60 m M^-1s^-1,r₂=372.86 m M^-1 s^-1).According to the structure of the 10%Gd-LRH nanosheets,the relaxation mechanism of novel 2D nanosheets as MRI CAs was discussed.4.The Eu³⁺and Gd³⁺co-doped rare earth hydroxide nanosheets were prepared by introducing Eu³⁺as luminescence center to optimize the multimode imaging capability of 10%-Gd-doped nanosheets.Combining the T₁ and T₂ relaxation times at3T clinical MRI scanner,cell fluorescence imaging and cytotoxicity,demonstrated the imaging capability of T₁-and T₂-weighted and cell fluorescent imaging and low cytotoxicity of Eu/Gd-NS@tta monolayer nanosheets,and has great development potential in multimode imaging.