The media used for density gradient centrifugation includes several different substances, each chosen for its specific density and properties.
Common Density Gradient Media
Here's a breakdown of commonly used gradient media, based on the provided reference:
| Media Name | Characteristics | Common Applications |
|---|---|---|
| Caesium Chloride | Forms very dense gradients, often self-forming | Separating DNA, RNA, and viruses |
| Sodium Metrizoate | Forms density gradients suitable for cell separation | Separating blood cells, isolating lymphocytes |
| Sucrose | Readily available, relatively inexpensive | Separating cell organelles, viruses, and some proteins |
| Ficoll | Polymer, forms low to medium density gradients | Separating blood components, isolating cells |
| Ludox® | Silica-based colloid, forms dense gradients | Separating viruses, macromolecules |
| Percoll® | Silica-based colloid, forms medium to high density gradients | Isolating cell organelles, separating cells, density-based separation |
| BactXtractor™ | Specific for bacterial cells | Isolating bacteria from complex mixtures |
Why Use Different Media?
- Density Range: Different media offer varying density ranges, enabling separation of components with a wide spectrum of densities.
- Compatibility: Some media are better suited for specific types of biomolecules or cells due to their chemical properties.
- Cost and Availability: Factors like cost and ease of access also play a role in the selection of a density gradient medium.
How Density Gradient Centrifugation Works
Density gradient centrifugation separates components based on their buoyant densities. A sample is layered on top of the gradient medium, and then centrifuged. Particles move through the gradient until they reach the position where their density matches that of the surrounding medium. This technique is used to isolate and purify cell organelles, viruses, nucleic acids, proteins, and various types of cells.
- Self-Forming Gradients: Some media, like caesium chloride, can form a gradient during the centrifugation process itself.
- Pre-Formed Gradients: Others, such as sucrose or Percoll®, are often prepared as pre-formed gradients before the sample is added.
In summary, density gradient centrifugation relies on the use of different media like caesium chloride, sodium metrizoate, sucrose, Ficoll, Ludox®, Percoll®, and BactXtractor™ to separate components based on their densities. The choice of media depends on the specific application and the desired separation outcome.
