Nucleic acid extraction kits usually adopt different principles to extract nucleic acids, and the common ones include the following:

Binding of Nucleic Acids to Silica Gel Membrane: Under certain high salt and low pH conditions, nucleic acids have a strong affinity for the silica gel membrane. In the nucleic acid extraction kit, lysis buffer is first added to the sample to lyse cells and release nucleic acids. Then, the lysate is added to the spin column containing the silica gel membrane. The nucleic acids in the lysate will bind to the surface of the silica gel membrane, while other cell components such as proteins and polysaccharides will not bind and can be removed by washing.
Washing and Elution: After the nucleic acids are bound to the silica gel membrane, washing buffer is used to wash the membrane to remove impurities that may be adsorbed. Finally, under low salt and high pH conditions, the elution buffer is added, which changes the binding environment of the nucleic acids and the silica gel membrane, so that the nucleic acids are eluted from the silica gel membrane, thus obtaining purified nucleic acids.

Coating of Magnetic Beads: The magnetic beads in the nucleic acid extraction kit are usually coated with functional groups such as silica, carboxyl, or amino groups. These functional groups can specifically bind to nucleic acids under appropriate conditions.
Binding and Separation: Similar to the silica gel membrane method, the sample is first lysed to release nucleic acids. Then, the magnetic beads are added to the lysate, and the nucleic acids will bind to the surface of the magnetic beads. By using an external magnetic field, the magnetic beads bound with nucleic acids can be quickly separated from the lysate and other impurities.
Washing and Elution: After separation, the magnetic beads are washed with washing buffer to remove impurities. Finally, the nucleic acids are eluted from the magnetic beads by changing the buffer conditions, and the eluted nucleic acids are the target products we need.

Liquid-Liquid Extraction: In this method, organic solvents such as phenol and chloroform are used. After the sample is lysed, phenol-chloroform-isoamyl alcohol mixture is added. Nucleic acids are soluble in the aqueous phase, while proteins and lipids are soluble in the organic phase. By centrifugation, the two phases are separated, and the nucleic acids are in the upper aqueous phase.
Precipitation and Washing: Ethanol or isopropanol is added to the aqueous phase to precipitate nucleic acids. The precipitated nucleic acids are then washed with 70% ethanol to remove salts and other impurities. After drying, the nucleic acids are dissolved in an appropriate buffer for subsequent use.

Ion Exchange: The ion exchange resin in the nucleic acid extraction kit contains functional groups that can exchange ions with nucleic acids. For example, anion exchange resins can bind to the negatively charged phosphate groups on nucleic acids. When the sample lysate passes through the ion exchange resin column, nucleic acids are retained by the resin through ion exchange, while other substances pass through the column.
Elution: By changing the ionic strength and pH of the elution buffer, the bound nucleic acids are eluted from the ion exchange resin. Different elution conditions can be used to selectively elute DNA or RNA, achieving the separation and purification of nucleic acids.