氮掺杂碳量子点为载体的MR/荧光双模态成像探针的构筑及成像性能研究

The effective integration of traditional mono-modal molecular probes is to obtain “integration” imaging probe provided with diverse imaging function. It is a method of improving the comprehensiveness and accuracy of early clinical diagnosis for disease. The program intends to design and synthesize a series of water-soluble functional iminazole ionic liquids. The nitrogen-doped carbon quantum dots will be synthesized controllably using chitosan as carbon source and nitrogen source in the presence of ionic liquids, and these ionic liquids play the role of reactant, dispersing agent and stabilizing agent. Then dual-modal nano imaging probe will be fabricated through the covalent introduce of biological targeting folic acid and Gd(Ⅲ) based complex modified with low molecular weight chitosan. The imaging probe will couple the fluorescence property of carbon quantum dots, specific targeting of folic acid to tumor cells with favorable MR imaging property of Gd(Ⅲ) based complex. The relationship between the structure of dual-modal imaging probe and imaging activity will be studied in details by means of various characterization methods. The possible reactive mechanism for cell imaging will be explained from thermodynamics and dynamics aspect. The potential of dual-modal imaging probe applying in living imaging and in vivo real-time monitoring will be preliminarily studied.

将传统单一模态的分子成像探针有效融合得到具有多种显像功能的“一体化”成像探针，是提高疾病早期临床诊断信息的全面性和准确性的途径之一。本课题拟设计合成一系列水溶性咪唑类功能化离子液体，以其为直接反应源、分散剂和稳定剂，以壳聚糖作为碳源和氮源，在特定的反应条件下，可控合成氮掺杂碳量子点，共价引入生物靶向分子叶酸和低聚壳聚糖修饰的Gd(Ⅲ)基配合物，构筑双模态纳米成像探针。该成像探针将氮掺杂碳量子点的荧光性能、叶酸对肿瘤细胞的特异靶向性与Gd(Ⅲ)基功能配合物的核磁成像性能相结合。运用一系列表征手段研究双模态成像探针的组成、结构与成像性能之间的内在关系，从热力学和动力学角度阐述其用于细胞成像的作用机理，并初步探讨该成像探针用于活体成像和体内实时监测的潜能。

利用多功能“一体化”成像探针对疑难疾病进行早期诊断，克服了单一成像模态的固有局限性，提高了早期临床诊断信息的全面性和准确性，这也是目前本领域研究的热点之一。本项目致力于以碳量子点为荧光成像单元，钆离子和Fe3O4纳米粒子分别作为T1和T2-MR成像单元，构筑有效的双模态纳米成像探针，通过各类分析手段表征其结构和形貌。研究不同碳源和氮源（壳聚糖或柠檬酸）、不同反应溶剂（水、乙酸溶液、离子液体或低共熔溶剂）等条件下制备所得的碳量子点的荧光特性以及细胞内的荧光成像性能，分析双模态成像探针在不同激发波长下的荧光发射特性和弛豫性能（r1和r2）。研究结果发现，在ChCl-Urea低共熔溶剂反应体系中，以柠檬酸为碳源，乙二胺为氮源，能够制备出高质量的碳量子点作为荧光成像载体，其荧光量子产率为8.4%，体现出激发波长依赖性的荧光特性，MTT结果显示低毒性，同时在RAW264.7活细胞内能够呈现出明亮的绿色荧光。此外，在碳量子点载体上链接钆离子和Fe3O4纳米粒子后所得到的双模态纳米成像探针由于表面掺杂原子的不同，呈现出激发波长无关的荧光特性，且荧光性能稳定，同时显示其具有超顺磁性，r1和r2分别为5.16和115.6 mM-1•s-1，能够同时应用于T1和T2-MR加权成像以及荧光成像。该研究工作的开展，为基于碳量子点框架载体的多模态“一体化”成像探针的构筑提供了新的方法，为实现多模态成像和成像治疗一体化提供了新的途径。