Abstract: Probes comprising a cardiolipin derivative covalently attached to a solid phase, other than through an allylic oxygen, are described. Methods of making the probes are also described. A cardiolipin analogue which is amino-derivatised at the end of one of the fatty acid side chains is reacted with an activated ester attached to a solid support. The probes are useful for diagnosis of anti-phospholipid antibody syndrome (APS), and for identifying and purifying cardiolipin binding proteins.