Benefits of Fluorescent Glass Microspheres
Sometimes researchers are looking for a durable high-temperature solvent-resistant particle that also has high visibility or fluorescent response. In this situation a microsphere made out of glass or ceramic would be preferred. Spherical shape may be essential for the project due to the sliding (ball-bearing) effect, uniformity of dimensions, or other unique properties of microspheres.
Unfortunately, fluorescent glass microspheres or fluorescent ceramic microspheres are difficult to source, primarily due to the specifics of the microsphere manufacturing process for these materials. Incorporation of fluorophore into glass or ceramic microsphere manufacturing often interferes with the formulation of the glass and hinders the process.
Manufacturing of Fluorescent Glass Microspheres
An elegant solution to this challenging problem is creating a Janus particle by coating half a sphere with a fluorescent or other high visibility durable coating. In this situation, the manufacturer has the flexibility of formulating the coating with any color additive or fluorophore with any desired spectrum response. Due to the transparent nature of the glass, the coating will be visible through the whole particle and provide the appearance and the functionality of fully fluorescent glass microspheres.
This patented coating process applies precision hemispherical coating to exactly half of each sphere. The coating is durable, inert, and capable of withstanding high temperatures and harsh solvents.
The coating doesn’t have to be fluorescent and can be applied to almost any core material, which doesn’t have to be glass. The extra benefit of using glass as a core is that it makes each microsphere individually and a significant quantity of microsphere in powder form appear fluorescent in daylight and provide respective bright fluorescent response under UV illumination.
Options for Fluorescent Glass Microspheres
When selecting fluorescent glass microspheres for a project, typically the researcher needs to select a suitable core material and the fluorophore for the coating, which is based on the desire fluorescent response under UV illumination.
The core can be glass or ceramic, as long as the material is available in spherical form and uniform size distribution. Sometimes density of the core material is important. In this case a specific formulation of glass may be used as the core microsphere material.
Fluorescent coatings are available in seven standard colors for scientists and engineers who require a fluorescent tracer of a specific emission spectra.
Seven standard fluorescent color coating options on glass with broad spectrum responses:
Blue Fluorescent Glass Microspheres (445nm peak emission) at 407nm excitation
Green Fluorescent Glass Microspheres (515nm peak emission) at 414nm excitation
Yellow Fluorescent Glass Microspheres (525nm peak emission) at 485nm excitation
Orange-Yellow Fluorescent Glass Microspheres (594nm peak emission) at 460nm excitation
Orange Fluorescent Glass Microspheres (606nm peak emission) at 577nm excitation
Red Fluorescent Glass Microspheres (607nm peak emission) at 585nm excitation
Violet Fluorescent Glass Microspheres (636nm peak emission) at 584nm excitation
For Particle Image Velocimetry (PIV) applications that typically use green lasers (530nm) as excitation sources, we recommend utilizing red fluorescent microspheres in conjunction with a 570-580nm high pass filter so only the fluorescent particles will be visible during imaging.
An example of a technical article that utilizes red fluorescent micropsheres is “A method for large scale implantation of 3D microdevice ensembles into brain and soft tissue” published in bioRxiv. In this paper, scientists describe a method for high-throughput implantation of ∼100-200 μm size devices which are here simulated by proxy microparticle ensembles:1
While generally applicable to subdermal tissue, our main focus and experimental testbed is the implantation of microparticles into the brain. The method deploys a scalable delivery tool composed of a 2-dimensional array of polyethylene glycol tipped microneedles which confine the microparticle payloads. Upon dissolution of the bioresorbable polyethylene glycol, the supporting array structure is retrieved and the microparticles remain embedded in the tissue, distributed spatially and geometrically according to the design of the microfabricated delivery tool.1
In this work, the authors used spherical and planar microparticles as substitute microscale devices. In lieu of active electronic microdevices or chemically infused microscale payloads, they chose two types of passive proxy particle types to study the effects of different geometries and material choices; (a) spherical polyethylene and borosilicate microspheres of size ∼100 μm were purchased from Cospheric (UVPMS-BR-1.090, HCMS-BSGMS-FMB, Cospheric, CA, USA), and (b) planar silicon chiplets measuring 100×100 μm on the side and 50 μm thick were microfabricated through a combination of photolithography and dry etching.1
- A method for large scale implantation of 3D microdevice ensembles into brain and soft tissue