We regrettably don’t have the ability to measure the surface charge of our particles, but based on many studies that have measured the surface charge of our particles, as well as our personal experience, we expect most uncoated particles to have a net negative surface charge. This includes our plain polystyrene, carboxylated polystyrene, amine polystyrene, and their equivalent dyed counterparts. Coated protein will likely take on the surface charge of the corresponding protein.

By default, we do not offer particles with a known positive surface charge. While amine groups are thought to contribute localized positive charge, the net charge of the particle surface is not necessarily positive. Positively charged particles can be created by further modifying our plain or carboxylated polystyrene, either through surface conversions or coatings with cationic polymers.

We measure the carboxyl titer for the vast majority of our carboxylated beads, and results can be found alongside the product by clicking on catalog number of interest. Silica carboxyl do not come with titer estimates, although we do conduct qualitative streptavidin binding tests to confirm carboxyl group reactivity.

Most of our protein coated products come with a binding capacity, which will be listed on the CoA and made available upon request.

Most protein-coated beads employ a base carboxylated bead, and the protein is subsequently covalently attached using EDAC-based methods. However, exceptions exist, so please inquire with our Technical group for more information.

Exact offerings depend on availability and product type. Size offerings generally start at 25 nm and go as high as 20 µm for our polystyrene beads, whereas silica is about 150 nm to 5 µm. Non-standard offerings may exceed these general ranges.

Most of our products are of a polymer composition, principally polystyrene, but potentially PMMA or other proprietary polymers. We also produce silica beads, as well as some polymer and non-polymer paramagnetic particles.

Polystyrene is generally considered non-toxic and is ubiquitously used in other industries that end up in direct contact with humans. Furthermore, many studies exist that cite the use of polystyrene or similar particles in cells and animal models. With that said, our products are for Research Use Only and have been supplied with added stabilizers that can be toxic to cells or other life. Individual use is at the user’s risk.

For PSI, we anticipate a refractive index of 1.59 at the 589 nm. For more RI values (and other info) visit our Material Properties page.

We do not measure the sphericity or surface roughness of our particles. In general, though, we expect the particles to be spherical. Acid-modified spheres (e.g. carboxylated) may have more associated surface roughness.

Many of our users approach us with this question. The desired size will vary depending on the intended use. If unsure, you should first consult the relevant literature; many times a similar use has been reported can be used as an initial basis for selection. Keep in mind that while we’re happy to guide in the process, ultimately the decision needs to be made by the user. See Technote 201A.

We do not evaluate the molecular weight of the polymer chains.

We do not produce porous beads, all offerings should be viewed as non-porous.

For the majority of our lots we do not offer SEM images. In limited instances, we have SEM images for select lots.

Particles will be provided at various concentrations depending on the type of product. For instance, we supply our plain polystyrene at 10% solids, or 100 mg of beads/mL. Particle count is not measured on most products unless it’s a speciality count product (such as our SureCount standards). Estimated counts are typically supplied on the product’s CoA and can be supplied on a requested basis as well.

Washing refers to an exchange of the suspending solution in which particles are suspended. Most users employ a centrifuge to pellet the beads, aspirate/decant the supernatant, then resuspend in the desired buffer type and volume. Washing can fulfill a variety of needs, including preparing the beads for various applications, or during coating procedures to remove residual reagents. See more in our Washing Technote.

See our centrifugation chart. Beads below 0.5 µm should use alternative techniques, such as spin filters (Vivaspin) or dialysis.

Beads can be dried down; we do so on a limited basis for some of our products as a standard offering. Drying is a bit of an art form, so users will need to optimize extensively if they intend to pursue. Some level of aggregates must also be expected. For quick experimental efforts, see Technote 203A for a general drying protocol .

Sure. Our polystyrene beads are stable in a wide variety of aqueous solutions, although do avoid organic solvents which will likely dissolve the beads. Crosslinked beads (look for DVB in the product description) will confer added resistance to temperature and organic solvents.  See our solvents listing; solvents not listed should be researched, or may be brought to our Technical group for review. Silica beads are much more chemically resistant and can be used in more challenging environments.

None of our products are provided sterile, although the majority do contain sodium azide to help prevent microbial growth. Autoclaving our particle suspensions is strongly discouraged, as it will likely cause partial to severe particle aggregation. Refer to our Technical Support Document 726, Decontaminating Microspheres for other suggested methods.

A variety of methods exist. The most popular is by using carboxylated beads to covalently link to the amine groups of proteins or antibodies (Technote 205), or by using an affinity method such as biotin-protein to our streptavidin coated beads (Technote 101). Adsorption is also a common method, and relies on non-specific hydrophobic, ionic and Van der Waals forces (Technote 204). Other options exist, and choosing which approach to use is ultimately an independent decision.

Protein needs will vary greatly based on the particle diameter, protein of interest and intended use. The gold standard is to titrate the protein against the bead, then monitor for subsequent stability and performance. Initial estimates can be derived from the available functional groups and by using our surface saturation equation in Technote 205.

Storage temperatures are mainly aimed at preventing microbial growth throughout the product lifetime. Freezing, however, will cause the particles to severely and irreversibly aggregate, forming what looks like precipitates.  Speciality surface-modified fluorescent particles will need to keep the corresponding fluorochromes stability profile in mind as well. For instance, phycoerythrin (PE) and its tandems are well known to be quite temperature-sensitive.

Stabilizers present will vary depending on the product. Consult the CoA or SDS for specific product info (can be found on the website with the product). In general, most polymer bead suspensions will feature a surfactant and sodium azide (used as an antimicrobial). Protein-coated suspensions tend to have further additives, such as BSA and EDTA. Uncoated silica and some magnetic microparticles are free of stabilizers, again, consult the product CoA.

Polymer microspheres should be stable under a wide range of conditions, and do not readily degrade. Exposure to very high temperatures or solvents can compromise the beads. Visit our Material Properties page and solvents/non-solvents listing for more information. Specific or unique conditions should be addressed with our Technical group before purchase.

Most suspensions of uncoated microparticles do not have an assigned expiration period. This is based on our expectation that the particles will not appreciably change over time, and is supported by our experience in handling particles. Some specialized uses or types of microparticles, however, do warrant expiration dating, including protein coated particles (due to the more labile nature of the protein), or particle standards (fluorescence, size, etc). In these instances, the expiration date will be printed on the CoA as well as on the bottle label. See more details about stability & storage here.

Beads are commonly used in phagocytosis experiments, especially fluorescent beads. See  Technical Document 727 – Phagocytosis and Phagocytosis References for more info.

QuickCal is a program used to support our Quantum MESF and Quantum QSC kits. We offer a variety of formats to accommodate the different resolutions a cytometer’s software may offer. To choose the appropriate template type, review the channel values listed on our fluorescence histogram and compare that to the channel values listed on our website. Most commonly the log/log format is appropriate.