Methods, compositions and articles of manufacture are provided for conducting specific binding assays to determine the concentration or presence of at least one analyte in a sample. At least two dendrimer-reagent preparations with different analyte specificities may be immobilized on a solid phase. Alternatively, at least one dendrimer-reagent preparation having multiple specificities may be immobilized on a solid phase. Immobilization is facilitated by coupling specific binding assay reagents such as polypeptide receptors or analytes with water soluble polymers. Such water soluble polymers, for example star polymers such as dendrimers, provide production advantages of lot-to-lot uniformity and homogeneity, and can enhance sensitivity due to low non-specific binding to the solid phase.