[Microspheres, nanospheres and flow cytometry: from cellular to molecular analysis].

Micro- and nanospheres are tightly associated with the development of flow cytometry. They are indispensable tools to optimize diffraction and fluorescence signals as well as for fluorescence calibration and cellular purification (magnetic micro- and nanospheres). They are also usefull to evaluate phagocytosis and to detect slightly expressed antigens. Recently, developments of microspheres-based flow cytometric assays have raised to quantify soluble analytes in biological fluids, cellular and tissue samples. The technology utilizes spectrally distinct fluorescent microspheres as a solid support for a conventional immunoassay, affinity assay or DNA hybridisation assay which is subsequently analyzed on a flow cytometer. Several multiplexed bead systems are now available facilitating the development of multiplexed assays that simultaneously measure many different analytes in few microliters of sample. Some recent applications with fluorescent microspheres coated with antibodies or oligonucleotides include cytokines and PCR products quantitation and single nucleotide polymorphism genotyping. Thus, multiplex assays using microspheres and flow cytometry technologies are exciting techniques which have the potential to contribute to the development of efficient diagnostic and research methods.