Applications of gold cluster compounds in immunocytochemistry and correlative microscopy: comparison with colloidal gold

In this review, we discuss the immunocytochemical literature with respect t o a comparison between conventional colloidal gold and gold cluster compoun ds as immunoprobes. The relative advantages and disadvantages of each of th ese types of particle for immunocytochemical applications are discussed. We present results from our own laboratories and those of others on the compa rison of these immunoprobes in selected experimental situations. These resu lts show the use of gold cluster compounds at both light and electron micro scope levels. At the ultrastructural level, gold cluster compounds have bee n used in pre-embedding labelling of cultured cells, and for labelling of u ltrathin cryosections and freeze-fracture preparations. Recently, fluoresce ntly tagged gold cluster compounds have become available. Using ultrathin c ryosections of human neutrophils as a model system, we demonstrate that a s ingle immunoprobe (i.e. a fluorescently tagged gold cluster compound) is a robust probe for correlative fluorescence and electron microscopy.