Density gradient centrifugation separates specific cell populations from biological particles based on the density range of the gradient medium and sample particles. We offer a broad portfolio of density gradient media for the separation or extraction of leukocytes, viruses, DNA, RNA, organelles, and many other applications. Our product line includes Histopaque iodinated gradient media for the cell separation of leukocytes, polysaccharides for the isolation of mammalian cells, colloidal silica media for the isolation of mammalian cells and organelles, and inorganic salts for the isolation of DNA, viruses and proteins.
Cell Separation With Accuspin System – Histopaque Medium
The popular ACCUSPIN™ system with Histopaque-1077 uses radiation-sterilized centrifuge tubes designed to create two separate chambers with a porous high-density polyethene (“frit”) barrier. This system allows anticoagulated whole blood to be added to the upper chamber without the risk of mixing with the Histopaque separation media in the lower chamber. Histopaque Density Grade Media allow clear separation of lymphocytes and mononuclear cells (ie, monocytes). Red blood cells aggregate and granulocytes become slightly hypertonic, increasing their sedimentation rate, and resulting in the formation of granules at the bottom of the ACCUSPIN™ tube.
Histopaque Iodine Gradient Media
Histopaque media are sterile, endotoxin-tested solutions of polysucrose and sodium diatrizoate, adjusted to precise densities. These ready-to-use separation media facilitate rapid and optimal recovery of viable cells from small volumes of whole blood. Produced under ISO 13485 quality management, Histopaque products with lot-specific performance tests provide consistent selective separation of blood cell lines, optimal separation of undistorted viable cells, and minimal foreign cell interference.
Percoll Colloidal Silica Media
Colloidal silica media are colloidal suspensions of polyvinylpyrrolidone (PVP)-coated silica particles with a diameter of 15-30 nm. PVP decreases the interactions of the particles with the biological material and stabilizes the colloid. Our Percoll colloidal medium has an extremely low osmotic force that changes little with density. Furthermore, the osmolarity of the gradients formed by centrifugation is easily adjusted by adding the appropriate amount of sucrose or buffer solution. Percoll gradients are ideal for isopycnic separations of cells, organelles, membrane vesicles, and even some viruses.
Our ion gradient media, composed of concentrated heavy metal salts, are used exclusively for isopycnic separations of nucleic acids. Caesium chloride and caesium sulfate are the most commonly used heavy metal salts with gradient densities up to 1.91 g/cm3. Other salts used include sodium iodide, sodium bromide, and rubidium salts.
Density Gradient Media with Non-Ionic Iodine
The structures of most iodinated compounds used in popular density gradient media are based on triiodobenzoic acid with an attached hydrophilic group to increase solubility. We provide denser iohexol solutions (eg, Nycodenz and Histodenz™) that minimize the dehydration of biological particles. Iohexol is nontoxic and is not metabolized by mammalian cells.
Our portfolio of nonionic polyhydric alcohol gradient media includes sucrose gradients that are widely used for rate zone separation of macromolecules and for isopycnic separation of viruses and cell organelles. Advantages include its stable nature, inertia, and low cost; while the disadvantages involve the concentrated and hypertonic nature of the solution. We also offer a glycerol solution that has a lower density than corresponding sucrose solutions, which prevents the activity of certain enzymes and is easily removed by vacuum.
We provide the most widely used polysaccharide medium, Ficoll, to overcome the high osmotic force problems that arise with the use of sucrose solutions. It is produced by the polymerization of sucrose molecules with epichlorohydrin to give a polysaccharide with an average molecular weight of 400,000. Ficoll solutions below 20% (w/v) have a density of 1.07 g/cm3 and are considered osmotically inert. The main disadvantage of the Ficoll solution lies in its more viscous nature than comparable sucrose solutions.