I don't know what application you have in mind for your nanogold conjugated aptamer: negative stain EM, cryo low-dose EM, plastic embedded samples? Depending on the technique different consideration come into play.

Generally, the 5 nm gold particles are pretty easy to visualize thanks to their size and electron density. For the same reasons, the 1.8 nm gold particles are more difficult to visualize. Given their small size, it can be tricky to see those smaller particles.

I completely agree with Holger.

Here are my comments:

If you choose negative staining, I would suggest to start with that, you will need carbon coated TEM grids (400 or 600 mesh). You have to glow-discharge the carbon-coated grids before sample preparation to make them hydrophilic (glow-discharge activation). As a negative stain, I would suggest ammonium molybdate (~ 1%-2%) over uranyl acetate. The density of uranyl acetate is high and can make visualization gold nanoparticles troublesome. A small addition of trehalose (~0.1%) to ammonium molybdate can help.

Good luck.

Oldrich

Instead of carbon-coacted grids, you can also use Formvar coating as a support for your particles. Expectedly, gold conjugates will also be visible without counterstain.

please see links:

https://www.researchgate.net/post/How_to_increase_hydrophilicity_on_formvar_carbon-coated_TEM_grids#55dbf02760614b699e8b4595

https://www.researchgate.net/post/How_can_I_achieve_bacteriophage_imaging_by_TEM

https://www.researchgate.net/post/How_to_treat_formvar_carbon_coated_grids_for_TEM_sample_prep

Dear all,

I really appreciate your valuable comments.