A method for the separation of a target molecule from a mixture is described. The method employs oil bodies and their associated proteins as affinity matrices for the selective, non-covalent binding of desired target molecules. The oil body proteins may be genetically fused to a ligand having specificity for the desired target molecule. Native oil body proteins can also be used in conjunction with an oil body protein specific ligand such as an antibody or an oil body binding protein. The method allows the separation and recovery of the desired target molecules due to the difference in densities between oil bodies and aqueous solutions.