The scientists used the technique to move a microlitre droplet of di-iodomethane a distance of 1.38 mm up a 12° gradient. This meant that the monolayer of molecular machines did a total amount of work against gravity of 1.2 × 10-8 J. The researchers say this is equivalent to tiny movements in a conventional machine raising an object to more than twice the height of the world's tallest building.

David Leigh and colleagues synthesized rotaxane molecules and allowed them to self-assemble into a monolayer on a gold substrate. Applying a beam of ultraviolet light with a wavelength of 240-400 nm caused parts of the molecule to rotate, in a process known as photo-isomerization. This concealed short fluoroalkane segments on the rotaxane molecule, lowering the contact angle of the surface with both polar and nonpolar liquids.

To make a liquid droplet move, the team focused a light beam on one side of the drop. This created a gradient in the surface free energy along the length of the drop, resulting in motion of the droplet.

According to the researchers, the process leads to transport of an object on a length scale a million times larger than the initial change in molecular co-conformation caused by the light irradiation.

The researchers say their technique could have applications in lab-on-a-chip environments, in performing chemical reactions on a tiny scale without reaction vessels, and in drug delivery, smart materials and artificial muscles.

The researchers reported their work in Nature Materials and at the BA (British Association for the Advancement of Science) Festival of Science in Dublin, Ireland.