Combined fluorescent and gold nucleic acid probes

Abstract

Site-specific probes which incorporate both fluorophores and the 1.4 nm “Nanogold” gold particle have been prepared (Fig. 1). Specimens labeled with these probes may be imaged by fluorescence microscopy, then examined at higher resolution in the electron microscope without an additional gold-labeling step: this allows better specimen preservation and unprecedented correlation between the two sets of complementary data. In addition, the covalent gold attachment procedure allows the preparation of electron microscopy probes using small molecules, which cannot be coupled to colloidal gold.Two types of probes have been prepared. In the first, the Nanogold particle was covalently attached, via peripheral primary amine groups, to Hoescht-33258, a fluorescent dye which is specific for AT-rich regions of double-stranded DNA. Excess Hoescht-33258 was removed by membrane separation. The resulting reagent was tested in Chinese hamster ovary cells: results are shown in Figs. 2 and 3. Specific staining of the nucleus was observed both by fluorescence microscopy and in the light microscope, using silver enhancement (Danscher's procedure) to visualize the gold-labeled regions.