Fluorescent Microspheres – Properties and Applications

Fluorescent microspheres are round spherical particles that emit bright colors when illuminated by UV light. Ability to emit intense color under UV (black light) illumination provides contrast and visibility of microspheres relative to background materials. In addition to the benefits of conventional high quality microspheres, such as sphericity, smoothness and spreadability among others, fluorescent spheres offer extra sensitivity and detectability for analytical methods. For example, fluorescent microbeads are often used as traces to simulate spread of viruses in medical research.

Typical applications of fluorescent spheres include: testing of filtration media and systems, vial and container cleaning studies, flow tracing, flow visualization, and fluid mechanics studies, medical imaging and flow cytometry, fluorescence microscopy and photography, as well as biomedical technology research, qualification and validation of medical devices, biomedical diagnostics, process troubleshooting and process flow among others. Specifically fluorescent microspheres are often used for water- and air-flow testing and bead-based diagnostic applications. New unique applications of fluorescent spheres are being discovered daily.

75-90um Dual Response - Daylight & 365nm UV  20um-1000umFluorescent spheres have a unique ability to appear translucent (clear) and practically invisible under ordinary light, and emit intense visible color when energized by ultraviolet (UV) light. This effect allows scientists and engineers to design blind tests and controlled experiments (e.g. simulate spread of viruses) where the microspheres are invisible to the operator doing the procedure until after the fact, therefore, eliminating any operator bias and uncertainty in the validity of experiment. This unique feature of fluorescent microspheres has numerous applications in biomedical research and process troubleshooting.

Fluorescence occurs when a molecule absorbs energy in the form of light and then immediately releases this energy again in the form of light.

Excitation wavelength – characteristic wavelength that molecule absorbs

Emission wavelength – characteristic wavelength that molecule emits

Stokes shift – difference between excitation and emission wavelength

Quantum efficiency – ratio of emitted energy to absorbed energy

Currently fluorescent microspheres in a variety of excitation wavelength and emission wavelength are available which allows the differently colored microspheres to represent different experimental variables/conditions and be separated on the basis of either their excitation or their emission spectra.

Daylight fluorescent Yellow - Blue Green 365nm UV  microspheresThere are several different types of fluorescent polymer microspheres on the market that are manufactured from different materials and manufacturing processes, making them suitable for a variety of applications. UV fluorescent microbeads vary based on size: submicron, 1-5 micron, 10-15 micron and 20 micron ? 1000 micron (1mm). Color under daylight conditions and UV (black light) illumination conditions can be optimized for each application to either color-match with the background or provide high contrast. Specific density of the fluorescent microparticle can be important if the spheres need to be suspended in a fluid and desired buoyancy is required. In addition, stability of a specific fluorescent colorants under environmental effects and photobleaching varies and may be important.

Typically microspheres that are heavily loaded with fluorescent colorants are the most highly visible with the strongest fluorescent response. Those processes that embed the colorant into the polymer matrix of the sphere, rather than just providing the coating on the surface, usually result in the most stable fluorescing properties minimizing the possibility of leaching of the colorant into the fluid.

The products can be stored at room temperature and can be dispersed in aqueous media or air without degrading their fluorescent properties.

Cospheric LLC, a Santa Barbara based microtechnology company specializes in fluorescent microspheres in diameters from 1micron to 1000micron (1mm). The stability, uniformity and reproducibility of Cospheric microspheres is controlled to very tight specifications. Extensive selection of colors and particle sizes is available in dry form in small volumes (500mg) or large volumes (1000kgs+). Microspheres in custom colors in both daylight and UV illumination, as well as custom sizes and specific gravity, can be produced with short leadtimes.


Written by: Yelena Lipovetskaya
CTO, Cospheric LLC, Santa Barbara, CA

Article originally published on www.cospheric.com