The following framework is intended to provide guidance for customers’ handling and storage of microsphere raw materials.    


I. Uncoated general-purpose microspheres

We do not assign formal expiration dates to uncoated general-purpose microspheres (with the exception of Europium chelate*). We consider them to be chemically inert, and expect that they will be stable indefinitely (years) provided that they are stored and handled properly.  General recommendations are as follows:

Polymer / silica / magnetic microspheres supplied in suspension:  

Do:

  • Use refrigerated storage (2-8C) to safeguard against growth of opportunistic microorganisms
  • Use aseptic technique (or as near as possible) to reduce the risk for microbial contamination.  
  • (Many suspensions contain an antimicrobial agent; consult product COA , PDS or SDS for details.)

Do NOT: 

  • Freeze, which will likely cause irreversible aggregation
  • Expose to extreme conditions that would cause degradation of the particle matrix, e.g.:
polymer -> extreme heat, organic solvents;
silica -> strong acid (e.g. hydrofluoric acid);
magnetic -> depends on matrix / exposed iron oxide:
ProMag, ProMag HP, Magnefy (polymer magnetic) -> some crosslinking, confers some heat / solvent resistance
COMPEL (polymer magnetic) -> not crosslinked, matrix is more sensitive than others to physical force, organic solvents, etc.
BioMag (silanized iron oxide clusters) -> sensitive to high temperatures (>50C) and prolonged exposure to lower pH

Fluorescent microspheres supplied in suspension:  

In addition to general recommendations:

Do:

  • Maintain in original opaque bottle to safeguard against photobleaching.
  • Protect from light as needed during use.  

Europium chelate microspheres supplied in suspension:

Europium (III) microspheres have expiration dating that is 2 years from the date of shipment. In addition to general recommendations:           

Do:

  • Maintain in original opaque bottle to safeguard against photobleaching.
  • Protect from light as needed during use.  

Do NOT:

  • Expose microspheres to extreme heat. Eu (III) is a chelated complex, and as such, is sensitive to high heat,
    e.g. 70C. Testing should be performed to ensure compatibility with elevated temperature (>RT).               

Visibly dyed microspheres supplied in suspension:

See general recommendations.

Functionalized silica (COOH or NH2) supplied dry:

Do:

  • Store tightly sealed at RT; once opened, headspace of vials may be purged with inert gas (e.g. Ar) as moisture contamination is expected to hydrolyze the silanized bead surface over time.

Do NOT:

  • Store uncoated (unconjugated) COOH or NH2 silica as an aqueous suspension as the silanized surface will hydrolyze over time.  See PDS 702, Storage and Stability, for more information.     


If particle suspensions are handled in accordance with these recommendations, we expect shelf lives in excess of 3 years at the customer’s facility. Though we expect that the products will remain stable during this period and beyond, we suggest that they be re-evaluated annually to ensure that they continue to meet performance expectations.


Affinity ligand-coated general purpose microspheres

General handling and storage recommendations provided in above section I. apply.  

General-purpose affinity-ligand coated microspheres, including streptavidin, protein A/G, lectins (WGA, ConA), biotin, and secondary antibody coatings on polymer, silica or magnetic microsphere matrices are assigned an expiration date that is 12 months from shipment. These products are supplied in defined buffers that contain an antimicrobial agent. See specific product documentation for details.