基于氧化铁纳米颗粒和碳点的新型磁性荧光双功能纳米神经示踪剂的创制和应用

Early and accurately evaluating restorative effects of peripheral nerve injuries is crucial for selecting treatment strategies and predicting functional outcomes, however, current clinical detection methods can’t satisfy this requirement. Neuroanatomical tracing technique is able to assess nerve regeneration more directly and accurately. Traditional neural tracers have several drawbacks, such as complex operations, weak fluorescence signal and poor photostability. Carbon dots are fluorescent nanoparticles with excellent biocompatibility, and are widely used in bioimaging recently due to its unique optical properties. Therefore, we are committed to create new nano-neural tracing techniques for in vivo detection. The latest synthesized red-emission carbon dots-based neural tracers have better imaging sensitivity and photostability, however, their shallow imaging depth and low spatial resolution limit their applications in tracing imaging in vivo. In order to remedy the shortcomings of single optical imaging, we plan to create a dual-functional nano-neural tracer with magnetic resonance imaging and fluorescence imaging applications by labeling neurotropic substances with magnetic iron oxide nanoparticles and carbon dots; moreover, this tracer will be used to study the peripheral nerve regeneration qualitatively and quantitatively to deeply understand the functional recovery after nerve injuries. Through this study, we hope to provide a convenient and directly observable in vivo neural tracer, which is of great significance to improve the restorative effects of peripheral nerve injuries.

早期准确评估周围神经损伤后修复效果对于治疗策略选择和预测功能转归至关重要，而目前临床检测仍无法满足要求。神经示踪技术能更直观准确地评估神经再生水平。传统神经示踪剂有操作复杂、荧光强度弱及光稳定性差等缺点。碳点是一类生物相容性极好的荧光纳米粒子，近年来因其独特的光学性质在生物成像研究中广泛应用。因此，本课题组致力于研发可活体检测的新型纳米神经示踪技术。最新合成的红色荧光碳点神经示踪剂具有较好的成像敏感性和光稳定性，但其成像深度浅、空间分辨率低，仍不能满足活体示踪成像。本课题组拟利用磁性氧化铁纳米颗粒和碳点同时标记亲神经物质，制备兼有核磁共振成像和荧光成像的双功能纳米神经示踪剂，弥补纯光学成像的不足；并应用其对周围神经损伤后再生水平进行定性、定量研究，深入了解神经损伤后功能恢复过程。通过本研究，期望为周围神经损伤提供一种便捷、可直接观测的活体神经示踪剂，对改善周围神经损伤修复效果具有重要意义。

早期准确评估周围神经损伤后修复效果对于治疗策略选择和预测功能转归至关重要，而目前临床检测仍无法满足要求。神经示踪技术能更直观准确地评估神经再生水平。传统神经示踪剂有操作复杂、荧光强度弱及光稳定性差等缺点。因此，本项目组致力于研发可活体检测的新型纳米神经示踪技术。核磁共振成像（MRI）作为神经成像技术可以很好地克服荧光成像穿透深度不足的缺陷，从而实现非侵入性地监测深部组织内解剖细节的变化。磁性氧化铁纳米颗粒作为MRI和光声成像（PAI）造影剂具有优良的生物相容性和安全性。所以，本项目组将氧化铁纳米颗粒（Fe3O4@COOH）和生物素化葡聚糖胺（BDA）偶联制备了具有MRI和PAI双模态成像功能的纳米神经示踪剂Fe3O4@COOH-BDA，进一步通过微球（microspheres）包封技术起到控释和缓释效应，即制备microspheres-Fe3O4@COOH-BDA。微球能很好地限制示踪剂的泄漏，从而实现神经解剖结构的良好可视化，并改善长期追踪效果。本项目主要研究内容包括：示踪剂的制备表征；示踪剂的生物相容性评价；示踪剂促进背根神经节细胞轴突生长评价；示踪剂促进周围神经损伤修复的体内研究；示踪剂在周围神经损伤成像中的应用。本项目研究结果表明，该示踪剂具有较高的空间分辨率和较深的穿透性，MRI可以快速定位周围神经的示踪部位，而PAI的高灵敏度提供了实时的微观结构信息。因此，Fe3O4@COOH-BDA的MRI和PAI的理想组合有助于准确追踪周围神经系统，并且相对长期的纵向监测结果也为评估神经再生水平提供了重要信息。此外，这种多功能顺行神经示踪剂具有潜在的神经治疗功能，即Fe3O4@COOH-BDA可能影响轴突生长锥中铁离子的浓度，从而调节细胞骨架行为，激活细胞粘附分子，最终诱导轴突延伸。因此，我们的示踪剂可以实现神经修复过程中轴突水平的长时间、高精度和实时成像监测，是一种新型的活体神经成像模式，扩大了核磁共振神经成像（MRN）的应用范围，具有良好的临床应用前景。此外，我们期望通过本研究能为周围神经精准靶向的活体示踪成像提供新技术和新思路，也为周围神经损伤诊疗一体化研究提供可靠性的依据。