Visualizing Biological Samples in Liquid Solution by Electron Microscopy

Abstract

Liquid water is essential to life on earth. The cell, the basic component of all living organisms, functions through the action of proteins in a liquid environment. Consequently, the ability to directly visualize protein structure at nanometer-resolution in a liquid environment would dramatically advance mechanistic understanding of protein function in cellular activity. Current techniques in imaging biological samples in liquid solution are limited by micrometer scale resolution, Fluorescence-labeled, dehydrated, fixed, stained or frozen in ice.Here, we report an electron microscopic approach for imaging label-free, near-native biological samples in liquid environment. By passing electrons through a thin layer of liquid-buffer sealed within a micro-chamber, we directly visualized the structure of proteins, viruses, bacteria and human cells at nanometer resolution, even achieved their 3D structures. For example, the electron tomographic 3D reconstruction (Figure) of a label-free living bacteria, Magnetospirillum magneticum in growth medium showed a smooth outer shell and internal components, such as poly(3-hydroxybutyrate) (PHB), chromosomal mass (CR), magnetosomes (MG) and internal septal layer. These results suggest the method offers both a general-purpose and high-throughput tool for imaging the structure of biological samples in near-native physiological liquid conditions.View Large Image | View Hi-Res Image | Download PowerPoint Slide