Antibody/signal-generating moiety conjugates are disclosed that include an antibody covalently linked to a signal-generating moiety through a heterobifunctional polyalkyleneglycol linker. The disclosed conjugates show exceptional signal-generation in immunohistochemical and in situ hybridization assays on tissue sections and cytology samples. In one embodiment, enzyme-metallographic detection of nucleic acid sequences with hapten-labeled probes can be accomplished using the disclosed conjugates as a primary antibody without amplification.