Aggregates consist in many cases of microorganisms attached to an organic matrix.
Modern equipment, such as epifluorescence microscopes, flow cytometers and confocal laser scanning microscopes, requires or works best with fluorescently marked objects. Therefore, there is a great need for a fluorescent dye to visualise polysaccharides associated with aggregates. Like proteins, polysaccharides are very heterogeneous in their 3-dimensional structure. Moreover, saccharides are very hard to modify covalently in water at natural pH levels. In contrast, very small particles such as bacteria were seen better with propidium iodide.