Alexa Fluor 594 FluoroNanogold Fab' fragment of goat anti—mouse IgG is covalently conjugated with uniform, 1.4 nm—diameter gold clusters and our bright, red-fluorescent Alexa Fluor 594 dye (which is spectrally similar to Texas Red dye). FluoroNanogold conjugates can be used as probes in immunoblotting, light microscopy, electron microscopy or with fluorescence microscopy.