基于介孔硅的核磁荧光双模态靶向纳米探针制备及机理研究

Dual-modal imaging simultaneously by MRI and fluorence can offer a precise spatial tomograph of a tumor as well as reveal the details of biological activity inside tumor cells. In this project, we intend to prepare a specific targeted nanoproble with MRI-fluorescence dual modality for molecular imaging of cancer. The nanoprobe, a new nanocompoiste, is developed with mesoporous silica as the framework and assembled with nanoscale gold rod, Gd2O3 clusters and fluorescent molecules DiR through synthesis. Theoretical apporaches to the structure versus property of the nanocomposite, based on the density functional theory and molecular dynamics, provide in silico performance of the nanocomposite and serve as a primary guide for the design of the nanoprobe. Systematical characterizations of the nanocomposite are carried out,including its capabilty for both in vitro and in vivo MR and fluorescent imaging,its acute nanotoxicity and biocompatibility etc. Image-fusion technique is employed to fuse the independent imagings by MRI and fluorescence, respectively, into a dual-modal image. The key points of the study include below:.1. The interactions among the magnetic Gd2O3 cluster, nanosized gold rod and fluorescent molecules DiR; the mechanism underlying either the enhancement or quenching of fluorence luminescence and MR imaging in relation to the interactions. 2. Investigate the optimal mode and site for couppling between fluorescent molecule DiR/targeted molecule and carrier (silica); obtain a steady configuration of the nanocomposite and minimize the possiblity of toxic Gd ions, targeted and DiR molecules disassocited from silica, causing not only loss of dual-modal imaging but also toxicity of free metal ions. The current study achieves double outcomes, first for its certain practicality in early diagnosis of tumor, second for its value in understanding the mechanism underlying the fundamental interplay between magnetism and luminescence.

磁共振荧光双模态成像可同时准确提供肿瘤的空间定位和高灵敏度揭示肿瘤细胞分子内部的活动细节。以介孔硅为载体，借助纳米组装技术合成一种核磁-荧光双模态纳米复合材料，经表面修饰在其表面挂接鼻咽癌靶标分子，形成靶向核磁-荧光双模态分子影像探针。通过超快荧光寿命谱分析、基于密度泛函理论的能量-构型计算及大分子团簇动力学模拟，本项目拟：1.探讨核磁模态的Gd2O3磁性团簇、纳米Au团簇及荧光模态DiR基团三组元间模态耦合的增强-淬灭机理；2.考察荧光基团、靶标分子与载体的耦合位点、方式及其相应的能量构型差异，获得灵敏稳定的靶向组合，减小靶向组合在体内发生断裂降解的可能性。对制备的双模态纳米探针进行动物模型的短期毒性测试及双模态成像评价，并实施双模态的影像融合。本项目不仅研发一种具有实用价值的靶向核磁-荧光双模态分子影像探针，也从学科交叉层面来探讨上述介观系统的光磁耦合作用新特征及其机制的物理基础。

项目相关背景：本项目延续并拓展了前一个国家基金项目研发的单一核磁模态材料(Gd2O3@MCM-41)的用途，核磁-荧光双模态在精度和灵敏度方面优势突出。该材料除了作为肿瘤的核磁共振诊断造影，我们还成功将其用于脑干细胞的标记示踪。.主要研究内容、结果及科学意义。新材料方面：（1）系统研究了双模态复合光磁造影材料Au@Gd2O3@MCM-41的性能及模态增强机理：该材料具有增强的核磁成像能力(优于目前商用螯合物类核磁造影剂Gd-DTPA)和较低的短期生物毒性。（2）合成制备了SiO2@(Y0.95-xGdxEu0.05)2O3.该材料是一种具有核壳结构置换掺杂的光-核磁双模态纳米复合材料。在该项工作中，我们很好地掌握了用水热合成法制备具有核壳结构光-磁双模态纳米复合材料的关键工艺，为后续的其它类似结构材料的制备打下了实验基础。(3)通过两步水热反应合成核壳结构的磷酸盐纳米颗粒的创新性方法，合成制备出TbPO4：Ce3@TbPO4:Gd3。这是另一种新型六方核壳，结构并具有优异的光-核磁双模态性能纳米复合材料，其中光模态强度增强达200倍。此外，对该材料进行了一系列的结构性能表征，结果表明：所合成的纳米颗粒TbPO4：Ce3@TbPO4:Gd3分散均匀，尺寸合适，结晶性良好，具有优良的光学性质及较高的核磁弛豫率，且毒性低，细胞相容性好。.增强机理研究方面：采用Gaussian和Quantum Expresso 的考虑自旋极化的密度泛涵理论对不同尺寸的Gd2O3团簇的结构、电子和磁学性质进行了第一性原理计算,探讨了团簇尺寸、结构、对称性、配位数、平均键长、结合能的变化规律，为后续研究金纳米结构和核磁-光学模态的相互作用及该类复合结构材料中的增强核磁成像能力的新机理提供基础。该机理与用螯合物Gd-DTPA包裹纳米金Au团簇获得的增强机制不同。螯合物具有树枝状开放结构导致纳米颗粒整体的翻转率降低而影响电子自旋-核自旋的偶极相互作用，由此而改变核磁纵向弛豫率。而本文工作制备的掺Gd介孔SiO2材料为闭合团簇，弛豫率的增强源自于纳米金Au团簇和核磁纵向弛豫原子Gd离子之间的直接耦合。上述基于第一性计算的核磁增强机理已经正式发表，使原来的核磁增强经典Solomon-Bloebergen-Morgan（SBM）理论难于处理的多元体系变得可行。