Density gradient centrifugation separates specific cell populations of biological particles based on the density range of the gradient media 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 separation of leukocytes, polysaccharides for mammalian cell isolation, colloidal silica media for mammalian cell and organelle isolation, and inorganic salts for the isolation of DNA, viruses and proteins.
The popular ACCUSPIN™ System with Histopaque®-1077 uses radiation sterilized centrifuge tubes designed to create two separate chambers with a porous high-density polyethylene barrier ("frit"). This system allows the addition of anticoagulated whole blood to the upper chamber without risk of mixing with the Histopaque® separation media in the lower chamber. Histopaque® density grade media allows a clear separation of lymphocytes and mononuclear cells (i.e., monocytes). Erythrocytes aggregate and granulocytes become slightly hypertonic, increasing their sedimentation rate which results in pelleting at the bottom of the ACCUSPIN™ tube.
Histopaque® media are sterile, endotoxin-tested solutions of polysucrose and sodium diatrizoate, adjusted to precise densities. These ready-to-use separation media facilitate the 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 testing provide consistently selective separation of blood cell lines, optimal separation of viable undistorted cells and minimal extraneous cell interference.
Colloidal silica media are colloidal suspensions of silica particles coated with polyvinylpyrrolidone (PVP) with a diameter of 15-30 nm. PVP decreases the particle interactions with the biological material and stabilizes the colloid. Our Percoll® colloidal media has extremely low osmotic strength that changes little with density. Also, the osmolality of the gradients formed by centrifugation are adjusted easily by adding appropriate amount of sucrose or buffer solution. The Percoll® gradients are ideal for the isopycnic separations of cell, organelles, membrane vesicles, and even some viruses.
Our ionic gradient media, comprised of concentrated heavy metal salts, are exclusively used for isopycnic separations of nucleic acids. Cesium chloride and cesium sulfate are the most widely used heavy metal salts with gradient densities of up to 1.91 g/cm3. Other salts used include sodium iodide, sodium bromide and the rubidium salts.
The structures of most iodinated compounds used in the popular density gradient media are based on tri-iodobenzoic acid with a hydrophilic group attached to increase their solubility. We provide denser iohexol solutions (e.g., Nycodenz® and Histodenz™) that minimize the dehydration of biological particles. Iohexol is nontoxic and not metabolized by mammalian cells.
Our portfolio of polyhydric alcohol nonionic gradient media includes sucrose gradients that are widely used for the rate-zonal separation of macromolecules and for isopycnic separation of viruses and cell organelles. The advantages include their stable nature, inertness and low cost; whereas the disadvantages involve the concentrated and hypertonic nature of the solution. We also offer glycerol solution having lesser density than the corresponding sucrose solutions, thereby preventing the activity of certain enzymes while being removed easily through vacuum.
We provide the mostly commonly used polysaccharide medium, Ficoll® to circumvent the high osmotic strength issues arising with the use of sucrose solutions. It is produced by the polymerization of sucrose molecules with epichlorohydrin to give a polysaccharide with the 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 Ficoll® solution lies in its more viscous nature than the comparable sucrose solutions.
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