A Simple Method to Visualize and Assess the Integrity of Lysosomal Membrane in Mammalian Cells Using a Fluorescent Dye

Fluorescent dyes have been used as “nanosensors” for visualization and determination of various processes occurring inside a cell, or intracellular events, such as cell cycle progression and intracellular trafficking. Here, we describe a novel use of acridine orange to visualize lysosomes and discriminate cells with healthy lysosomes from cells with damaged lysosomes in two different types of mammalian cells: fibroblasts and macrophages. This method allows assessment of lysosomal membrane integrity upon exposure to various foreign particles, i.e., engineered nanoparticles. The uniqueness of this method enables investigators to acquire fluorescent images with a dye that is susceptible to photo-bleaching under UV light. These acquired images bolster the quantitative data, providing a visual representation of the cell morphology as well as assess its nucleus and lysosomes.