The purpose of a coloured or fluorescently dyed particle is its visibility with the naked eye or by a detector. By adding a dye to the particle it reduces signal to noise due to the contrast between the particle and its environment. Applications for these particles are countless. By modifying the surface of the particles, antibodies or proteins can be conjugated to their surfaces, making them ideally suited for diagnostic assay development, for instance for lateral flow assay development. We offer coloured and fluorescent dyed microspheres from Thermo Scientific, VDo Biotech and Applied Microspheres.