PtdIns-(4,5)-P2-biotin is an affinity probe which allows the PIP2 to be detected through an interaction with the biotin ligand. This design allows PtdIns-(4,5)-P2 to serve as a general probe for any protein with a high affinity binding interaction with inositol-(4,5)-diphosphate phospholipids, such as phosphatidylinositol 3-kinase, PTEN, or PH-domain-containing proteins.