CD Bioparticles provides silica particles with a high amount of covalently bound fluorescence dye in the silica matrix. The fluorescent silica nanoparticles are available with red fluorescence (excitation: 569 nm, emission: 585 nm), green fluorescence (excitation: 485 nm, emission: 510 nm) and blue fluorescence (excitation: 354 nm, emission: 450 nm). Different surface functionalities including Si-OH, NH2 and COOH enable covalent binding of proteins, antibodies, oligonucleotides, and other molecules. These particles have broad applications in immunoassays such as flow cytometry, membrane checks, as well as flow investigations.