1.    What speed should I centrifuge them at?
2.    What do you mean by washing?
3.    Can I dry the beads?
4.    I want to put the beads into a different solution, is that ok?
5.    Are the beads provided sterile? If not, is it ok if I autoclave them?
6.    Can beads be used for phagocytosis?
7.    What QuickCal program should I select?
8.    What is the surface charge or zeta potential of your particles?
9.    Do you have positively charged particles?
10.    Do you measure the amount of carboxyl or amine groups on your beads?
11.    Do you measure the binding capacity of your beads?
12.    How can I attach my protein to your particles?
13.    How does Bangs attach their proteins for protein coated particles?
14.    How much protein should I use to coat?
15.    What sizes do you offer?
16.    What are your beads made of?
17.    Are the beads toxic? Can I use them in animals?
18.    What is the refractive index?
19.    Are your particles smooth and spherical?
20.    What size bead should I use?
21.    What is the molecular weight of your beads?
22.    Are your beads porous?
23.    Do you have SEM imaging you can share?
24.    What is the particle concentration and particle count?
25.    Your storage recommendations mention store at 2-8C, and not to freeze. Why is that? I thought these were inert particles?
26.    What stabilizers do you provide in your particle suspensions?
27.    Do your particles melt, break, or otherwise dissolve?
28.    What is the expiration policy?

Handling

1. What speed should I centrifuge them at?
See our centrifugation chart. Beads below 0.5 µm should use alternative techniques, such as spin filters (Vivaspins) or dialysis.

2. What do you mean by washing?
Washing refers to an exchange of the suspending solution the particles are suspended in. Most often users employ a centrifuge to pellet the beads, aspirate/dump out 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.

3. Can I dry the beads?
Beads can by lyophilized or otherwise 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, especially freeze drying, so users will need to extensively optimize if they intend to pursue, and some level of aggregates must be expected. For quick experimental efforts, see Technote 203A for a general drying protocol .

4. I want to put the beads into a different solution, is that ok?
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 non-comprehensive solvents listing, solvents not listed should be researched, or brought to our Technical group for review. Silica beads are much more chemically inert, and can be used in more challenging environments.

5. Are the beads provided sterile? If not, is it ok if I autoclave them?
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.

Application specific

6. Can beads be used for phagocytosis?
Beads are commonly used in phagocytosis experiments, especially fluorescent beads. See  Technical Document 727 - Phagocytosis and Phagocytosis References for more info.

7. What QuickCal program should I select?
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.

General product info

8. What is the surface charge or zeta potential of your particles?
Regrettably we 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 of uncoated particles to have a net negative surface charge. This includes our plain polystyrene, carboxylated polystyrene, amine polystyrene, and their equivalent dyed counterparts. Protein coated will likely take on the surface charge of the corresponding protein.

9. Do you have positively charged particles?
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.

10. Do you measure the amount of carboxyl or amine groups on your beads?
We measure the carboxyl titer for the vast majority of our carboxylated beads, 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.

11. Do you measure the binding capacity of your beads?
Most of our protein coated products come with a binding capacity which will be listed on the CoA, and made available upon request.

12. How can I attach my protein to your particles?
A variety of methods exist, most popular is using carboxylated beads to covalently link to the amine groups of proteins or antibodies, or an affinity method such as biotin-protein to our streptavidin coated beads. Adsorption is also a common method, an relies on non-specific hydrophobic, ionic, and Van der Waals forces. Other options exist, and choosing which approach to use is ultimately an independent decision.

13. How does Bangs attach their proteins for protein coated particles?
Most protein coated beads employ a base carboxylated bead, and the protein is subsequently covalently attached using EDAC based methods. Exceptions exist, inquire with our Technical group for more info.

14. How much protein should I use to coat?
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 using our surface saturation equation in Technote 205.

15. What sizes do you offer?
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, please contact us for needs outside this.

16. What are your beads made of?
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.

17. Are the beads toxic? Can I use them in animals?
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.

18. What is the refractive index?
We anticipate a refractive index of 1.59 at the 589 nm. For more RI values (and other info) visit our Material Properties page.

19. Are your particles smooth and spherical?
We do not measure the sphericity or surface roughness of our particles. In general we expect the particles to be spherical. Acid modified spheres (e.g. carboxylated) tend to have more associated surface roughness.

20. What size bead should I use?
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.

21. What is the molecular weight of your beads
We do not evaluate the molecular weight of the polymer chains.

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

23. Do you have SEM imaging you can share?
For the majority of our lots we do not offer SEM images. In limited instances we have client-supplied or other third party SEM images for select lots. If you have the ability to SEM image and would like to do so, contact our Technical group to discuss.

24. What is the particle concentration and particle count?
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 also be supplied on a requested basis.

Storage and stability

25. Your storage recommendations mention store at 2-8C, and not to freeze. Why is that? I thought these were inert particles?
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, PE and it’s tandems are well known to be quite temperature sensitive.

26. What stabilizers do you provide in your particle suspensions?
Stabilizers present will vary depending on the exact bead product, consult the SDS for specific product info (can be found on the website with the product). In general most suspensions will feature a surfactant and sodium azide (used as an anti-microbial). Protein coated suspensions tend to have further additives, such as BSA and EDTA.

27. Do your particles melt, break, or otherwise dissolve?
No. Particles 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 info. Specific or unique conditions should be addressed before purchase with our Technical Group.

28. What is the expiration policy?
Most microparticle suspensions do not have an expiration period assigned. 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 the bottle. See more details about stability & storage here.