List is arranged by microsphere type:

• REGULAR-- plain or undyed
• DYED-- colored, including fluorescents
• SILICA
• SUPERPARAMAGNETIC
• ProActive® PROTEIN-COATED

Regular Microspheres and Dyed Microspheres are sub-divided by surface chemistry:

• Non-Functionalized includes microspheres with plain hydrophobic or polystyrene surface, and plain silica surface.
  
  
• Carboxylate Functionalized refers to 3 kinds of COOH surface groups. First, there are those made by copolymerization of unsaturated short chain mono-carboxylic acids , like acrylic or methacrylic acid, with styrene. Next, there are those made by polymerization of maleic anhydride with styrene (the anhydride hydrolyzes with time to the dicarboxylic acid, maleic acid). Last, there are a few microspheres which have been made with a short, C₂ to C₆, spacer arm extending out from the microsphere surface.
  
  
• Amino Functionalized or nitrogen-containing compounds like R-NH₂, primary and quaternary aliphatic amines, hydrazides, Ar-NH₂, aromatic amines, and pyridines.
  
  
• Other Surface Functionalized includes aldehyde, amide, chloromethyl, epoxy, hydroxyl, and sulfonate surface groups.

Within each type the microspheres are arranged by stock number (keyed to mean diameter) or magnetite content. Each stock number includes the mean diameter of a unique lot of microspheres. Each new manufacturing lot of an established product has a separate stock number.

Please do NOT assume that look-alike products are replicate lots. They may have been made by different processes, especially kind and amount of surfactants. Ask us to help you choose replicates of the same formulation or choose different products. We guarantee our replicates within narrow limits.

Mean diameter (<2 µm) is usually determined by transmission electron microscopy and the standard deviation(s.d.) is listed, if known. If standard deviation is not reported, usually the microspheres were measured by dynamic light scattering (DLS, or quasielastic light-scattering, QELS), which does not include s.d. Other methods may have been used, especially for the larger microspheres (>2 µm). Please inquire if interested in specific measurements for any lot. Unless otherwise stated, c.v. (coef. of variation) is guaranteed to be <3% (Silica is <10%).

Polymer description details polymer or monomers and other ingredients in each lot of microspheres. Abbreviations for monomers and other items are explained in the end-of-list legend. Excitation and emission wavelengths for fluorescent microspheres are included. Other ingredients are sometimes listed. Generally the microspheres are dispersed in an aqueous solution of sulfonate or carboxylic (fatty) acid surfactant. A few surfactant-free lots are marked (ask if you need others).

% Mag. equals magnetite content of superparamagnetic microspheres as a percentage of total solids content of microspheres. Original recipes are for 12, 20, 40, & 60% Fe₃O₄; encapsulated ones are ~20, 30, & 40%.

Color is listed for dyed microspheres, with indication of intensity (dark or light), where appropriate. Ask us to help you choose the right color for your job.

Density for plain and dyed microspheres ranges from ~0.9 g/ml for polyolefins to 1.05 for polystyrene, to 1.19 for polymethylmethacrylate, up to 1.5 for certain chlorinated or brominated styrene polymers and 1.96 g/ml for silica. Magnetic microspheres have densities of 1.2 - 2.3 g/ml, depending on magnetite content.

Surface groups are listed for microspheres where functional groups have been deliberately introduced. If no surface group is listed, the microspheres, usually polystyrene, will have a low level of negatively charged sulfate (-SO₄-) surface groups-- usually enough to yield microspheres stable in pure water. For covalent-coupling, try any of the microspheres with functional surface groups. We can help you choose the right group for your use and can offer coupling protocols.

Surface charge density is titrated and reported for many microspheres with surface functional groups, such as COOH groups. Results are reported as microequivalents of acid or base per gram of microspheres (µeq/g). From this and the diameter we calculate the parking area or area occupied by a single active group such as COOH or NH₂. You can compare this number to the close-packed area per molecule of a monolayer of functional groups (20-25Å^2/ COOH group). Thus, if a microsphere has a parking area ~25Å^2/ group, it is judged to have a monolayer of COOH groups on the surface- enough for many chemical links witha protein or other ligand to be covalently-linked to the surface. Parking area values therefore allow you to compare likely protein-coating efficiencies of different sized microspheres.

Product Class Most of our products, labelled "Std", for "standard" materials are produced regularly and are available as replicate lots. We also make many one-of-a-kind products by request for a particular customer. These are listed as "Rsch" for "research" lots.

Price Schedule: Decoded on last page of printed list.

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