Cell staining is an experimental technique that utilizes dyes or fluorescent probes to bind with specific intracellular structures or molecules, thereby enabling the visualization of cellular morphology, the localization of proteins, the detection of ion concentrations, or the assessment of cellular function through changes in color or enhanced fluorescent signals. The underlying principle of this technique is based on the specific binding or chemical reactions between dye molecules and their target analytes (such as DNA, proteins, or calcium ions); notably, certain probes (e.g., Fluo-4AM) require intracellular enzymatic activation before they can respond to changes in target concentration and emit a detectable signal. This technique encompasses a wide variety of methods-including nucleic acid staining (e.g., DAPI, Hoechst), protein immunostaining (e.g., immunofluorescence, Western blot), live-cell functional staining (e.g., calcium probes, mitochondrial membrane potential dyes), and histochemical staining (e.g., H&E staining, Masson staining)-and is widely applied across fields such as basic research, disease diagnosis, drug screening, and cellular functional analysis. As such, it stands as an indispensable core tool in modern life science research.