What is density gradient centrifugation?
Figuring out how to separate cells is an important part of any medical researcher’s job. There is a multitude of ways to classify different types of substances and the correct process often depends on what you are trying to isolate. One of the fastest and cheapest ways to classify a sample based solely on physical characteristics is centrifugation.
Density Gradient Centrifugation
The centrifugation process allows scientists to separate substances based on their shape and size. Samples are placed in a centrifuge, a machine designed to spin liquid solutions at high speed. The mixing or rotation causes the mixture to experience a centrifugal force that pushes the larger particles from the centre to the bottom and the smaller ones to the top. Larger components react to force more than smaller components.
In a density gradient medium for cell separation centrifugation, the process is similar. The samples are still placed in a centrifuge, but the ultimate goal is not to sort them by size. The spin of the centrifuge causes the denser particles to move toward the outer edge. These particles have more mass and are carried further by their inertia. The less-dense particles then settle towards the centre of the sample. This creates a solution ordered in layers by particle density from lowest to highest.
Principles of density gradient centrifugation
Each particle has a specific set of physical characteristics; the properties of its biological components that can be used for separation and isolation. Density gradient centrifugation focuses on two: size and density. The time required for this process depends on the size of the particles. Larger particles will reach their position of stability sooner, while smaller particles will take longer to cross the zone of larger particles and occupy 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 that is used to aid in the isolation or separation of cells. These products can not only speed up the process but can also increase purity and yield. By preventing particles from clumping, creating a fixed divider, or removing residual red blood cells, the reagents can greatly increase the efficiency of density gradient centrifugation.
Differential centrifugation
Differential centrifugation is another centrifugal separation method that is based on the mass of a particle. Since cells of different sizes already behave differently, the process is performed without a reagent or medium. Differential centrifugation is sometimes considered a simpler form of centrifugation.
It is used to separate 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 on which the process is based. Differential centrifugation may be easier, but density gradient centrifugation can classify particles of a much smaller size.
Results
Centrifugation of all kinds is beneficial to scientists because it collects substances for further experimentation or medical uses. Helps remove contamination and impurities in samples so that specific groups of cells or particles can be effectively isolated and studied.
Density gradient centrifugation and differential 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 overall efficiency.
