Amdex high-performance conjugates offer a novel approach to obtaining significantly improved sensitivity for high-sensitivity assay development. Improvement is gained without fundamental alteration to assay protocols. The conjugates are based on novel chemistry that facilitates conjugation of multiple enzyme molecules (alkaline phosphatase or horseradish peroxidase) to a single streptavidin or antibody molecule via a dextran backbone. In most traditional ELISA systems, the conjugates can be substituted directly for the existing HRP or alkaline phosphatase conjugate.