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Density Gradient Centrifugation

October 2020

Figuring out how to separate cells is an important part of any medical researcher’s job. There are a multitude of ways to sort different types of substances and the right process often depends on what you’re trying to isolate. One of the quicker and cheaper ways to sort a sample based only on physical characteristics is with centrifugation.

Density Gradient Centrifugation

The process of centrifugation allows scientists to separate substances based on their shape and size. Samples are placed into a centrifuge — a machine that is designed to spin liquid solutions at a high speed. The mixing or rotating causes the mixture to experience a centrifugal force that pushes larger particles from the center toward the bottom, and smaller to the top. The larger components react to the force more than those smaller components.

In density gradient centrifugation the process is similar. The samples are still placed into a centrifuge, but the end goal is not to sort them by size. The spinning from the centrifuge causes more dense particles to move to the outside edge. These particles have more mass and are carried further by their inertia. Less dense particles then settle towards the center of the sample. This creates a sorted solution that is layered by particle density from least to most.

Principles of Density Gradient Centrifugation

Each particle has a specific set of physical characteristics; the properties of its biological makeup  that can be used for separation and isolation. Density gradient centrifugation focuses on two — size and density. The length of time required for this process is dependent upon the size of the particles. Larger particles will reach their position of stability earlier, whereas smaller particles take longer to pass through the larger particle zone and take up a position deeper in the gradient.

Density Gradient Reagents

A reagent is any mixture or substance used in chemical analysis or experimentation. In density gradient centrifugation, the reagent is a product used to assist in isolation or separation of the cells. Not only can these products speed up the process, they can also increase the purity and throughput. By keeping particles from clustering, creating a set divider, or eliminating residual red blood cells, the reagents can greatly increase the efficiency of density gradient centrifugation.

Differential Centrifugation

Differential centrifugation is another centrifugation separation method that is based on a particle’s mass. Since different sized cells already behave differently, the process is done with no reagent or medium.

Differential centrifugation is sometimes considered a simpler form of centrifugation. It is used for separating cells and organelles while density gradient centrifugation is used for molecules and particles. The main difference between the two centrifugation methods is the type of physical properties in which the process is based on. Differential centrifugation might be easier, but density gradient centrifugation is able to sort particles of a much smaller size.

Results

Centrifugation of all types is beneficial to scientists because it harvests substances for additional experimentation or medical uses. It helps to remove contamination and impurities in samples so specific groups of cells or particles may be effectively isolated and studied.

Centrifugation can also be used to speed up other processes by mixing samples faster. Cell separation methods such as BACS or FACS can be supplemented with centrifugation to increase the overall efficiency.

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