MRI造影剂研究虽然取得诸多进展，但在肿瘤早期诊断方面还面临挑战。如何在肿瘤较小时测到信号，一方面要提高单位浓度钆的弛豫率，另一方面要提高钆在肿瘤部位富集效率。面对早期诊断重大需求，本项目拟构建基于多孔金纳米海绵的空间限阈效应、红细胞膜包裹、适配体靶向的高弛豫率高肿瘤富集造影剂。以弛豫理论为依据，在金纳米海绵孔里载一定尺寸钆基树型分子，因纳米孔限阈效应，将会极大提高单位浓度钆的弛豫率。为了提高钆在肿瘤部位富集效率，一方面利用红细胞膜整合技术在纳米海绵表面包裹上红细胞膜，提高载体在活体内稳定性；另一方面，构建HER2高表达工程化细胞，通过Cell-SELEX筛选高特异识别肿瘤细胞膜上HER2的适配体，将适配体与可自组装进红细胞膜的三种疏水分子交联，可实现适配体在红细胞膜上的自组装修饰。本项目以期探索构建高弛豫率高肿瘤富集MRI造影剂的一般规律，为其在肿瘤早期诊断的应用提供理论依据和实验基础。

Many achievements have been reported in the design of magnetic resonance imaging contrast agents, but we are still facing big challenge in early diagnosis of cancers by MRI. In order to sensitively detect the tumor in the early stage, in one hand we need to significantly improve the relaxivity (r1) per gadolimium(III). In the other hand we need to remarkably increase the accumulation effect of contrast agents in tumor. In this proposal, we plan to design and construct porous gold-nanosponge geometrically confined, erythrocyte membrane-coated and aptamer-targeted contrast agents with high relaxivity and high tumor accumulation, then systematically study the tumor magnetic resonance imaging of these agents. These contrast agents will be constructed as following: First, the nanoporous gold nanosponge will be synthesized with the controllable particle size and pore diameter. The several generations of biocompatible lysine dendrimer will be synthesized, then coupled with Gd-chelate (Gd-DOTA) with defined structures (then the defined molecular sizes). These Gd-DOTA-dendrimers with different molecular sizes will be loaded inside nanoporous structure of gold nanosponge. Based on the classical theory for predicting the efficiency of contrast agents, the geometrical confinement effect of nanoporous structure should dramatically enhance the relaxivity. Second, Gd-DOTA-dendrimer loaded gold nanosponge will be coated with erythrocyte membrane. Properties of erythrocyte membrane such as the structure and surface proteins have been taken as designing cues to devise the new delivery platform with long circulation and super stability in vivo. Finally, to endow the nano-carrier with high specific targeting efficiency, the DNA aptamer for HER2 protein on cell membrane will be isolated through Cell-SELEX and the engineered targeted cell line which is overexpressed HER2 on the control HER2-negative cell line. The aptamer is then conjugated with three kinds of hydrophobic molecules (lipid, cholesterol, cyclodextrin), and the synthesized conjugate is then inserted and self-assembled into the lipid bilayer of erythrocyte membrane to allow stable anchoring of the targeting aptamer on the membrane surface. This project will systematically investigate the synthesis procedure, characterization, in vitro and in vivo MRI imaging, especially the relationship between the geometrical confinement effect and the sizes of nanopores and dendrimers. It is expected to reveal the general mechanism for the construction of MRI contrast agents with high relaxivity and high tumor accumulation based on porous gold-nanosponge geometrically confined, erythrocyte membrane-coated and aptamer-targeted contrast agents. This study will open a new direction for developing new types of high relaxivity contrast agents based on different aptamers and erythrocyte membrane coating, then promoting clinic early diagnosis for various cancers.