14.6 FluoSpheres and TransFluoSpheres Microspheres for Tracing

FluoSpheres and TransFluoSpheres polystyrene microspheres 1 satisfy several prerequisites of ideal long-term biological tracers. Because the dyes in our microspheres are incorporated throughout the microsphere rather than just on its surface, the fluorescence output per microsphere is significantly greater than that obtained from protein or dextran conjugates (Table 6.6) and is relatively immune to photobleaching and other environment-dependent effects. FluoSpheres and TransFluoSpheres microspheres are also biologically inert and physically durable, and they are available from Molecular Probes with a large number of uniform sizes and surface properties. Furthermore, their spectral properties can be freely manipulated during manufacture without altering their surface properties. Our current carboxylate-modified fluorescent microspheres have much higher surface charges than were previously available, making them more hydrophilic and thus more useful as tracers. The additional carboxylate groups also make it easier to couple the microspheres to proteins and other biomolecules. See Section 6.5 for an extensive discussion of the properties of our FluoSpheres and TransFluoSpheres polystyrene beads. Molecular Probes also makes numerous fluorescent microsphere products that are useful as standards for imaging (Section 24.1) and flow cytometry (Section 24.2). Availability of intensely fluorescent, highly uniform microspheres in different colors and sizes permits diverse applications in tracking particles and cells, tracing fluid dynamics and amplifying signals. In addition, measuring the effect of various interventions on regional blood flow is an important quantitative application of fluorescent microspheres. Using a mixture of beads of different sizes, each labeled with a different fluorescent color, researchers can discriminate the size dependence of uptake or transport of microspheres in vivo in cells, capillaries, lung or other tissues.2 Our smallest microspheres can be microinjected into cells (see below) or are actively taken up by phagocytosis (Section 16.1).