What is the difference between PBS and PBST?

Phosphate-buffered saline (PBS) is a buffer solution frequently used in biological applications such as washing cells, transportation of tissues and dilutions. PBST is phosphate-buffered saline solution with a low-concentration detergent solution, such as 0.05% to 0.1% Tween™ 20. PBST is commonly used as a wash solution in Western blot and ELISA assays. Without damaging the antigen/antibody complex, PBST can effectively remove excel materials from W.B. membranes and microtiter plates.