What does an assay buffer do?

In general, a buffer is a solution that resists changing its pH level even when acidic or basic components are added to it. For assays, this makes it very useful for maintaining a desired pH (often physiological pH, but not always) even during extended or multi-step experiments.

Buffers consist of a weak acid/base pair, meaning a weak base and its conjugate acid, or vice versa. This allows the solution to remain at equilibrium and neutralize the addition of other components without appreciable change to pH level. The degree to which pH is sustained upon additions of acids or bases is referred to as the buffer capacity of a particular solution and typically has a range of approximately two, centered around the pKa of the primary acid or base. For procedures that require specific conditions, buffers are incredibly useful for sustaining and preserving stable solutions. Other buffer recipes are formulated to accomplish specific tasks, such as cell lysis or reagent preparation.

For recipes of common buffers, see ‘Additional Resources’ below for a link to the interactive Buffer Preparation and Recipes tool.