In chemistry, an affinity group is a chemical group that has a specific affinity for a particular atom, molecule, or functional group. Affinity groups can be used to selectively modify or target certain chemical species in a mixture or reaction. For example, a biotinylated affinity group can be used to selectively bind to and isolate proteins that have a specific affinity for biotin. Other examples of affinity groups include antibodies, aptamers, and lectins, which can selectively bind to specific antigens, nucleic acids, or carbohydrates, respectively. Affinity groups are commonly used in biochemical and biophysical studies to isolate, purify, or detect specific molecules or interactions.