Direct Observation of DNA at a Molecular Scale Level by Three-Dimensional Fourier Filtering Method

三维傅立叶滤波法在分子尺度直接观察DNA

基本信息

批准号：
13450036
负责人：
TAKAI Yoshizo
金额：
$ 6.53万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13450036/
关键词：
Transmission Electron Microscope DNA Molecular structure Bio Medical Sample Aberration-Free observation Phase Electron Microscopy Spherical aberration Correction Low electron dose

项目摘要

High-resolution transmission electron microscopy (HRTEM), at present, enables atomic level observation. However, the resulting image do not always show atomic structures precisely. Because, the image of the atomic structure is often distorted by multiple scattering of electron waves in the crystal and by aberrations ill the image-forming lenses. To solve the latter requirement, we proposed a new method called three-dimensional Fourier filtering method (3D-FFM), which enables us to observe spherical aberration-free phase and amplitude images separately. In the processing, a filtering shape function extracts only the linear component that appears -on a so-called Ewald sphere and the function works well for improving the S/N ratio by excluding the non-linear components and, quantum noises of the image, which effectively works for the biological sample observation under au extremely law electron dose conditionIn this study, the three-dimensional Fourier filtering method (3D FFM) has been successfully applied to observe a deoxyribonucleic acid (DNA) in the molecular scale level. To avoid the deterioration of the image quality cased by the contrast of the supporting film, a holey nano-sized gold grid was used and the DNA that was bridged over on the holey grid by a freeze drying method was observed. The processing made it possible to observe a spherical aberration-free phase image of the DNA with high contrast at in-focus condition. In the phase image of the DNA, periodic fine structures with intervals of 3.4-4.0 A, which seem to correspond to the distance between adjacent base pairs, were partially observed, though it seems to be heavily damaged. If we can reconstruct the DNA image by smaller dose of the electron, more,detail structures of the DNA will be, resolved, which is now under investigation

目前，高分辨率透射电子显微镜（HRTEM）可以实现原子级观察。然而，所得图像并不总是精确地显示原子结构。因为，原子结构的图像经常因晶体中电子波的多次散射以及成像透镜的像差而失真。为了解决后一个要求，我们提出了一种称为三维傅里叶滤波方法（3D-FFM）的新方法，它使我们能够分别观察无球差的相位和幅度图像。在处理过程中，滤波形状函数仅提取出现在所谓的埃瓦尔德球上的线性分量，并且该函数通过排除非线性分量和图像的量子噪声，可以很好地提高信噪比，有效地应用于非极律电子剂量条件下的生物样品观察。本研究成功地应用三维傅立叶滤波方法（3D FFM）在分子尺度水平上观察脱氧核糖核酸（DNA）。为了避免支撑膜对比度造成的图像质量劣化，使用多孔纳米尺寸金网格，并通过冷冻干燥方法观察桥接在多孔网格上的DNA。该处理使得在对焦条件下观察具有高对比度的 DNA 无球面像差相位图像成为可能。在DNA的相位图中，可以部分观察到间隔为3.4-4.0 A的周期性精细结构，该结构似乎与相邻碱基对之间的距离相对应，尽管它似乎受到严重损坏。如果我们能用更小的电子剂量重建DNA图像，更多的DNA细节结构将被解析，目前正在研究中