Osmotic pressure is the pressure that needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane. It is caused by the difference in solute concentration between two solutions separated by a semipermeable membrane.
One biochemical technique based on osmotic pressure is dialysis. Dialysis is a process that uses osmotic pressure to separate molecules based on their size and charge. In dialysis, a semipermeable membrane is used to separate a mixture of molecules into two compartments, a dialysis bag and the surrounding solution. The molecules that are small enough to pass through the pores of the membrane will diffuse out of the dialysis bag and into the surrounding solution, while larger molecules will remain inside the bag.
The osmotic pressure of the surrounding solution is carefully controlled to prevent the loss of small molecules and the entry of large molecules into the bag. This allows for the purification of biomolecules such as proteins and nucleic acids, which can be separated from smaller molecules such as salts and sugars. Dialysis is commonly used in biochemistry to purify proteins, enzymes, and other macromolecules.