Calcium phosphate is one of the oldest methods used for DNA transfection. In this method, a DNA-calcium phosphate precipitate is formed that can be taken up by cells, thereby delivering the DNA into the cells. The exact mechanism by which this happens is not fully understood, but it is believed that the DNA-calcium phosphate precipitate is endocytosed, or engulfed, by the cell and then breaks down within the cell, releasing the DNA.

To perform calcium phosphate transfection, a solution of calcium chloride is mixed with a solution containing the DNA. This mixture is then added to a solution containing a phosphate buffer. The calcium and phosphate ions react to form a precipitate, which also encapsulates the DNA. This mixture is then added to the cells, and over time, the cells take up the DNA-calcium phosphate precipitate.

One advantage of the calcium phosphate method is that it can be used to transfect a large number of cells at once, and it is relatively inexpensive compared to some other methods. However, the method can be somewhat finicky and requires careful optimization to achieve good results. It also tends to be less efficient and more toxic than other methods, such as lipofection or electroporation.

There are commercially available calcium phosphate transfection kits that contain pre-formulated solutions and detailed instructions to simplify the process. Examples include the ProFection Mammalian Transfection System from Promega and the CalPhos Mammalian Transfection Kit from Takara Bio. These kits can help to improve the efficiency and reproducibility of the method.