Overview

Cells are the basic units of life, and due to their extremely small size, they cannot be directly observed with the naked eye. It was not until the invention of the microscope in the seventeenth century that cell observation became possible. The light microscope (LM) uses visible light to magnify objects through an optical magnification system (eyepiece and objective lens) by several hundred times for observation. It can be directly used to observe unicellular organisms or cultured cells in vitro and observe the structures and morphology of cells after fixation and staining. The resolution can reach 0.2 μm, much finer than the resolution of the naked eye (0.2 mm), and is convenient to use, making it the most widely used equipment for microscopic observation today. In addition to the commonly used ordinary light microscope, there are many different types of optical microscopes, such as phase contrast microscopes (distinguishing areas with different densities), differential interference contrast microscopes (observing the movement of living cell particles and organelles), fluorescence microscopes (facilitating the identification of proteins labeled with different fluorophores and the tissue structures they form), laser scanning confocal microscopes (used for the localization and dynamic changes of subcellular structures and components), and super-resolution microscopy (including total internal reflection fluorescence microscopy, single-molecule imaging-based PALM/STORM methods, 4π microscopy, STED microscopy, and structured illumination microscopy).