In molecular biology, TBST (or TTBS) is a mixture of tris-buffered saline (TBS) (a buffer solution) and Polysorbate 20 (a polysorbate-type nonionic surfactant). Polysorbate 20 is also known as Tween 20, a commercial brand name. It is a common detergent used in many buffers for washing nitrocellulose membrane in western blotting and microtiter plate wells in ELISA assays. Tris is a buffer that maintains a pH of 7–9.2.