You may have noticed the reference to gold enhancement in the article on Nanogold® for Electron Tomography. Gold enhancement is a method for selectively enlarging gold nanoparticles, in order to render them visible either for direct observation by electron microscopy, or reveal their distribution and staining pattern by light microscopy or optical observation.
Gold enhancement works just like silver enhancement – but because it deposits gold instead of silver, it has several important advantages:
- Gold has a higher atomic number (Z) than silver, and hence has even higher contrast for EM applications, and you need less enhancement. A gold enhanced particle is easier to see in the EM than the same size silver enhanced particle.
- Gold is particularly effective for backscatter detection. Gold enhancement is therefore preferable for scanning electron microscopy (SEM) applications that use this method.
- Gold is not etched by osmium tetroxide or osmium tetroxide / uranyl acetate combinations. Use in place of silver enhancement where osmium etching is a problem.
- In light microscopic applications such as in situ hybridization, as well as in blots, background is lower than with silver enhancement, and sensitivity is just as high.
- Gold enhancement may be used in physiological systems. It is safe to use with saline and other halide-containing solutions. Gold does not precipitate with halides, as silver does.
- Meagher, C. K.; Liu, H.; Moore, C. P., and Phillips, T. E.: Conjunctival M cells selectively bind and translocate Maackia amurensis leukoagglutinin. Exp. Eye Res., 80, 545-553 (2005).
- He, W.; Kivork, C.; Machinani, S.; Morphew, M. K.; Gail, A. M.; Tesar, D. B.; Tiangco, N. E.; McIntosh, J. R.; and Bjorkman, P. J.: A freeze substitution fixation-based gold enlarging technique for EM studies of endocytosed Nanogold-labeled molecules. J. Struct. Biol., 160, 103-113 (2007).
Also in this issue: