The invention relates to methods for effecting qualitative and quantitative changes in the functional moieties expressed at the surface of cells and multi-cellular structures, and functional lipid constructs for use in such methods. In particular, the invention relates to functional lipid constructs and their use in diagnostic and therapeutic applications, including serodiagnosis, where the functional moiety is a carbohydrate, peptide, chemically reactive group, conjugator or fluorophore.