Fluorescent Tracer Microspheres – Properties and Applications

Benefits of Fluorescent Tracer Particles:

UV Fluorescent Tracer Microspheres

Fluorescent Yellow Polyethylene Microspheres 1.00g/cc – 10um to 1200um (1.2mm)
Cospheric Product Line: UVPMS-BY2-1.00

Fluorescent tracer particles are round spherical particles (fluorescent microspheres) 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, fluorescent tracer spheres offer extra sensitivity and detectability for analytical methods.

Fluorescence occurs when a molecule absorbs energy in the form of light and then immediately releases this energy again in the form of light. The following variables are typically considered:

  • 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

At Cospheric, we use proprietary manufacturing processes which allow us to fully incorporate a specific fluorophore into a spherical polymer matrix, enabling us to combine the benefits of spherical shape of the particle with the desired visibility/UV response of the fluorescent material. We fully embed fluorescent material into the polymer matrix during the manufacturing process.

Unlike other fluorescent materials that incorporate dyes or just coat the surface of the particle, Cospheric fluorescent tracer spheres are stable in solution and over time. The fluorescent material will not leach out into a fluid or degrade over time unless the polymeric sphere is melted, dissolved by a strong solvent, or fractured by high force. Cospheric fluorescent tracers may be stored at room temperature indefinitely and can be dispersed in aqueous media or air without degrading their fluorescent properties.

Optimization of Fluorescent Tracer Particles:

Color of the fluorescent tracers under daylight conditions versus under UV (black light) illumination conditions can be optimized for each application to either color-match with the background or provide high contrast. Currently fluorescent tracer 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. This also allows the researcher to select the material that will respond to their excitation method (e.g. type of laser) and provide emission signal in the desired range.

Density (specific gravity) of fluorescent microparticles may be important if the spheres need to be suspended in a fluid and desired buoyancy is required.

Particle size (sphere diameter) becomes critical when the fluorescent microspheres need to simulate or model a particle or a specific size or to penetrate openings/channels of specific dimensions, such as blood vessels.

Cospheric offers options of fluorescent tracer particles in a variety of colors, fluorescent response, sizes, densities. Custom combinations of the above variables are possible for unique applications.

Applications of Fluorescent Tracers:

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, environmental models, process troubleshooting and process flow among others. Specifically fluorescent tracer particles are often used for water-flow and air-flow testing and bead-based diagnostic applications. New unique applications of fluorescent spheres are being discovered daily.

Unique Color-Changing Fluorescent Tracers:

Dual Response Fluorescent Tracer Particles - Daylight & 365nm UV 20um-1000um

Fluorescent Polyethylene Microspheres – Clear in Daylight, Yellow-Green in UV Light – 10um to 1200um (1.2mm)
Cospheric Product Line: UVYGPMS

Some fluorescent tracer spheres (such as Cospheric UVYGPMS product line) have a unique ability to appear translucent (clear) and practically invisible when applied in a thin layer under daylight, yet emit intense highly-visible yellow-green color when energized by 365nm ultraviolet (UV) light. This unique feature of fluorescent microspheres has numerous applications in biomedical research and process troubleshooting.

These fluorescent spherical particles are designed to act as a hidden process tracer, for situations when it is advantageous to hide the fact that you have tracer particles on the surface and to be able to illuminate them on demand.

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.

Fluorescent Flesh-Tone Polyethylene Microspheres 1.00g/cc - 10um to 1000um (1mm)

Flesh-Tone Polymer Microspheres blend into most skin-tones
Cospheric Product Line: UVSKPMS

Fluorescent flesh-tone microspheres were developed at Cospheric in cooperation with Lydia Wigglesworth-Ballard of Old Dominion University for her dissertation research titled A Study of a Simulated Infectious Disease on Healthcare Workers’ Reaction, Knowledge, Attitudes, and Performance Towards Hand Hygiene. The goal of the study was to develop better tools and techniques for training and verification of cleanliness and hygiene protocols in a hospital setting.

Fluorescent flesh-tone microspheres, which are smaller than what unaided human eye can discern, were specifically designed to mimic the color of the skin and blend into the surface of most skin tones, appearing invisible to the staff performing the cleaning procedures under daylight illumination.

Cospheric flesh-tone fluorescent microsphere tracers can be placed in common areas or on top of mannequins and its spread later examined. After cleaning procedures are completed, the microspheres can be subjected to the ultraviolet (UV) illumination to check whether the target areas are indeed clean and whether the microspheres have spread to any other areas.

Color-matched fluorescent tracer particles

Invisible to the observer under daylight illumination, illuminated by UV light
Cospheric Product Line: UVSKPMS

In the above-mentioned study, Cospheric flesh-tone fluorescent microspheres were used as a “simulated infectious disease” (SID). The SID was used to simulate potentially infectious bacteria and was planted in areas on the patient mannequin and the bedside environment where colonization could potentially occur. The addition of SID to patient simulation scenarios allowed the staff to visualize the spread of infectious disease in a clinical setting and provide a visual impact of infection control lapses.

The first criterion outlined by the researcher was that the microspheres had to have the capability of blending into the skin color of the mannequin with minimal visibility with the naked eye. The second criterion was for the microspheres to spread by contact to other materials. The third criterion was for the microspheres to be visible with an external stimulus such as ultraviolet light (UV). Cospheric product met all the criteria as outlined.

The development of flesh-tone fluorescent microsphere product enabled the investigator to provide insight into lapses in hand hygiene made by healthcare workers in a simulated scenario, contributed to the healthcare worker’s understanding of how pathogens spread throughout a patient care setting by using SID to visually demonstrate the spread that can occur because of hand hygiene inactions, and facilitated the testing of a potential training-based solution to hand hygiene commitment for healthcare workers. 1

We are here to support your research and development needs. Please don’t hesitate to reach out to Cospheric Technical Support team to discuss your unique application.


  1. Wigglesworth-Ballard, Lydia. “A Study of a Simulated Infectious Disease on Healthcare Workers’ Reaction, Knowledge, Attitudes, and Performance Towards Hand Hygiene” (2015). Doctor of Philosophy (PhD), dissertation, Health Services Research, Old Dominion University, DOI: 10.25777/vc65-as75 https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1041&context=healthservices_etds[]