If you put gold nanoparticles in a graphene shell, you can see the molecules on the gold surface with an electron microscope, even in a liquid. This is what a Flemish-Spanish team reports in Nature Chemistry.

Gold nanoparticles have already been widely studied and applied, but less is known about what happens on the gold surface with the ever-present ligands. Indeed, electron microscopy (EM) allows one to see the nanoparticles very well, but small, light elements such as carbon are difficult to visualise. ‘In addition, most EM research is carried out in high vacuum, which is not a realistic environment for these molecules’, says Sara Bals, professor at the Department of Physics at the University of Antwerp. Bals’ group, in collaboration with Spanish researchers, therefore decided to make it even more challenging by looking at these surface molecules in liquid using transmission EM (TEM).

They did this by making ‘envelopes’ out of graphene. ‘We trapped the liquid with the gold nanoparticles and ligands between two layers of graphene’, Bals explains. ‘The advantage of graphene is that it is just a one-dimensional layer of carbon, which gives a negligible background signal in the TEM. In addition, the good thermal and electrical conductivity of graphene ensures that the electron beam causes virtually no damage to the ligands.’ The sheath structure limits the amount of liquid between the layers so that it does not further interfere with the already weak signal from the surface molecules. ‘It’s technically very well done and leads to new insights in materials science.’