There are several different types of media available for homogenizing samples, including both grinding beads and grinding balls. While grinding beads are a pool of beads within a given size range, grinding balls are spherical and precision ground to a specific diameter (for more information on grinding balls). OPS Diagnostics’ grinding beads are made of either zirconium silicate or silica (soda lime) and can be purchased in a variety of sizes and grades, as well as in bulk bottles or dispensed into disruption tubes.
The choice of beads to use for bead beating is a balance between performance and cost. Zirconium beads are extremely hard and dense, meaning that these beads are very durable and impart great force during homogenization. They are also extremely chemically stable. However, zirconium beads generate significant heat during the bead beating process, which can be deleterious to heat labile molecules. Zirconium beads can be purchased in the following diameters: 100 μm, 200 μm, 400 μm, 800 μm, 1.0 mm, 1.4 mm, 1.7 mm, and 3.0 mm. They are available in bulk (125 ml sterile bottle) or in pre-filled tubes that are ready-to-use.
Glass/Silica grinding beads are a less expensive alternative to zirconium beads. Silica beads are less dense and generate less heat during the bead beating process. For many applications, such as bead beating yeast, silica beads are very effective. Silica is also chemically stable in neutral and acidic solutions and reasonably hard. Silica beads can be modified through the addition of functional groups (i.e., amine, sulfhydryl, C3, and C8) by silane chemistry (see Coated Silica Beads). Molecules can be covalently coupled to beads by various chemistries, or adsorbed to the modified surface. Silica beads are available in the following diameters: 100 μm, 400 μm, 500 μm, 800 μm, and 4 mm. These can be purchased in bulk (125 ml sterile bottle) or in pre-filled tubes.
Three grades of grinding beads are produced by OPS Diagnostics, and include Acid Washed, Low Binding, and Molecular Biology Grade. Acid Washed grinding beads are washed with acid to remove small particles and contaminants from the media then oven dried and baked prior to bottling (see Acid Washed). Low Binding beads are acid washed beads that have undergone an additional proprietary process that reduces the amount of non-specific binding to the surface of the beads (see Low Binding). For assays potentially sensitive to nucleases and contaminating nucleic acids, Molecular Biology Grade beads are further processed and certified nucleic acid, DNase, RNase, and protease (see Molecular Biology Grade).