Fluorescent microsphere refers to fluorescent substances labeled on the surface of a microsphere (including surface coating) or microsphere with an inner structure containing fluorescent substances (e.g., embedding or polymerization); and, the microspheres are able to emit fluorescence as excited by external energy. As a kind of functional microsphere that carries fluorescent molecules, it is generally spherical externally. During nano-immunoassay featuring high sensitivity, strong specificity and being quantitative, etc., it selects fluorescent microspheres as its indicator. For this reason, it is used to measure bioactive compounds of a low content, such as proteins (e.g., enzyme, acceptor and antibody), hormones (e.g., steroid, thyroid hormones and phthalein hormone), drugs and microorganisms.

Fluorescent microsphere vectors are mostly organic or inorganic polymer materials. Based on differences in vectors and fluorescent materials, fluorescent microspheres can be divided into three major categories below：
1、Organic/inorganic fluorescent microspheres further divided into two types. The first type selects inorganic materials as its vector and organic compounds as its fluorescent materials; for example, silica gel can be used as an inorganic vector, in combination with fluorescein isothiocyanate, to prepare fluorescent microspheres. The second type selects organic materials as its vector and inorganic compounds as its fluorescent materials; for example, polymeric microspheres with active groups are used as vectors that bind to inorganic fluorescent nanocrystals (semiconductor microcrystal or metal oxide doped microcrystals) with active groups (e.g., amino acid and carboxylic acid).
2、Organic/inorganic fluorescent microspheres, such as fluorescent microspheres that select silica gel as vectors combined with inorganic fluorescent nanocrystals with active groups.
3、Organic/inorganic fluorescent microspheres, for example, fluorescent materials with free radical polymerization of functional groups and acrylic monomers with active functional groups (e.g., -OH and -COOH) are adopted to realize aqueous phase suspension polymerization, and crosslinking is achieved by using a cross-linking agent to produce polymer fluorescent microspheres of high light quantum, high stability and biocompatibility.

1、Applied in labeling and tracing: Fluorescent microspheres prepared by one or more fluorescent substances can be introduced on the surface of or inside the polymeric microspheres; not only can they be used for cell marking, bio-molecular marking and tracing in an active condition, but they are also applied in fixing protein molecules and track their functionalization process.
2、Applied in detection: Fluorescent microsphere with ligands binding to the test substance on surface are mixed with a radiologically labeled test object; and, regarding the test object binding to microspheres in the system, fluorescent materials can be excited by its radiant energy to produce fluorescence. As for test objects that cannot bind to microspheres, its radiant energy may disappear under water, which means that they fail to fulfill fluorescence excitation; on this basis, the test objects can be detected. Additionally, fluorescent microspheres may carry many fluorescent molecules, for which reason, weak excitation triggers strong signals. Therefore, only a little low energy radiation can produce fluorescence signals, which avoids radiation hazards caused by traditional radioactive microspheres. On the premise of maintaining detection sensitivity, the corresponding cost can be lowered.
3、Applied in immunoassay and drug screening:
(1)As fluorescent microspheres can be used as a diagnostic reagent, they have been applied in immunoassay. Fluorescent microspheres as the carrier for immobilization of diverse test objects are used for biological sample detection; and, different fluorescent microspheres correspond to different captured antibodies and can be used to identify various antigens. In this way, qualitative and quantitative detection of multiple antigens to be tested can be conducted.
（2）Surface of fluorescent microspheres is connected with receptors that bind to test objects and the test objects (ligands) undergo radioisotope labeling. Once mixed, the radioactive energy of test objects that bind to microspheres may cause the fluorescent material to emit fluorescence by means of excitation. Regarding test objects that cannot bind to microspheres, they cannot excite fluorescent materials to emit fluorescence as they are far away from the microspheres; in this way, the purpose of screening is achieved. High throughput screening (HTS), as a modern drug screening technique, means that robots and automated systems are used to identify a few active compounds that mutually interact with identified molecular targets from extensive samples. Progress in fluorescent microspheres facilitates development and growth of HTS.
4、Applied in immobilized enzymes and gene research:
（1）Enzymes may be fixed on fluorescent microspheres by means of physical absorption or chemical bonding. As three-dimensional shapes of enzymes have been immobilized, they not only possess high pH stability, heat stability and storage stability, but also can be easily separated from reactants. Moreover, the enzymes can be repeatedly used, that is, their availability factor is rather high. Therefore, immobilizing enzymes or other bioactivators on microsphere vectors is more beneficial to exert their functions.
（2）Fluorescent microspheres at a nanoscale are similar to biomolecules (e.g., nucleotide and protein) in their sizes; on their surfaces, masses of fluorescent molecular polymers are linked or embedded. By linking such microspheres to a nucleotide chain, the conventional fluorescent labeling technology in chip hybridization can be replaced; thanks to such substitution, fluorescence signal amplification is completed, so that the cost of manufacturing gene chips is enormously lowered.
5、Applied in reference substances and bioprobes:
（1）Importantly, fluorescent microspheres have been applied in determination of flow cytometry, such as reference substances for determination and calibration of cytometers.
（2）Polystyrene microsphere containing Cd Te quantum dots is prepared and Rabbit immune globulin is adsorbed on its surface; after that, the microsphere can serve as a protein sensitivity detection probe. Moreover, biofunctionally labeled quantum dot microspheres are featured with simplicity, rapidness and strong practicality, etc.