The Principal Investigators (PIs) propose to develop solid-phase heterogenous enzyme-linked immunosorbent assays (ELISAs). The proposed approach is to use phospholipid-based vesicles (liposomes) whose outer surfaces have been modified by the covalent attachment of 100 to 200 enzyme molecules as well as a variable, but smaller, number of specific analyte or antibody molecules. The potential signal enhancement that could be achieved by hundreds of attached enzyme molecules, rather than one or a few, to the analyte or antibody could result in a reduction of the limit of sensitivity of an ELISA by two orders of magnitude relative to current technology.