膨胀显微成像技术的原理及应用

膨胀显微成像技术（expansion microscopy,ExM）是一种新型超分辨成像技术。该技术借助可膨胀水凝胶均匀地物理放大生物样本，在常规光学成像条件下实现超分辨成像。ExM适用于细胞、组织切片等多种类型生物样本。蛋白质、核酸、脂质等生物大分子均可借助ExM进行超分辨成像。ExM可与共聚焦显微镜、光片显微镜、超高分辨显微镜联合使用，进一步提高成像分辨率。近年来，多种从基础ExM拓展而来的衍生技术进一步促进了该技术的实际应用。本文综述了ExM及其衍生技术的基本原理、ExM与不同成像技术联用的研究进展及ExM在不同类型生物样本中的应用进展，并对ExM技术的发展前景做出展望。

The Basic Principles and Application of Expansion Microscopy

Expansion microscopy (ExM) is a new super-resolution imaging technique. With the aid of expandable hydrogel, biological samples are uniformly physically amplified and can be imaged in super resolution by using conventional optical imaging microscopes. In ExM, after immunofluorescence staining, gel embedding, protease digestion and water swelling, the relative distance of fluorescent labeled molecules inside the biological samples was increased, so the sample can bypass the optical diffraction limit in conventional fluorescence microscope to achieve the super-resolution imaging. ExM is widely suitable for many types of biological samples such as cell and tissue sections. Proteins, nucleic acids, lipids and other biological macromolecules can also be imaged by ExM. ExM can be combined with confocal microscopy, light-sheet microscopy and super-resolution microscopy to further improve imaging resolution. In recent years, a variety of derivative technologies have been developed from base ExM, which further promotes the practical application of this technology. Protein retention expansion microscopy (proExM) can avoid complicated sample preparation process and directly image endogenous fluorescent proteins. Magnified analysis of the proteome (MAP) was suitable for super-resolution imaging in large biological samples. Iterative expansion microscopy (iExM) can increase the final expansion factor of biological samples to 16-22 times by changing the gel embedding steps. Cryo-expansion microscopy (Cryo-ExM) can provide better image fidelity. Expansion fluorescent in situ hybridization (ExFISH) and Click-ExM can achieve super-resolution imaging in nonprotein biomolecules, such as RNA, lipids, and polysaccharides. Expansion pathology (ExPath) can be used for clinicopathologic specimens imaging. The combination of ExM and light-sheet microscope can improve the image resolution to super-resolution level in the deep imaging depth. The application of ExM in super-resolution microscopy can further increase the resolution of images to 10-30 nm. In this paper, we reviewed the basic principles of ExM and its derivative technology, the research progress of combining ExM with different imaging technologies, the application progress of ExM in observing different types of biological samples, and the prospective of spreading ExM technology in the future.