MOF-based device could lead to self-propelling nanobots

A new type of ‘molecular motor’ that can buzz across a liquid surface like a speedboat could be an important step towards self-propelling microscopic machines such as nanobots.

Based around a highly porous metal organic framework (MOF), the device developed by researchers from the City University of New York works by manipulating the surface tension of the liquid.

The team turned this structure into a kind of fuel tank and motor for a tiny plastic boat with a slit in the hull. The MOF device is constructed to leak organic peptide molecules out of the slit, which propels the boat forwards.

In a paper in the latest issue of Nature Materials, researcher Hiroshi Matsui explained how his team filled the holes in an MOF with the peptide diphenylalanine and dropped the loaded MOF into a water bath.

Adding ethylenediaminetetraacetate (EDTA), a commonly used solvent that can grab and enclose metal atoms, to the water bath caused the MOF to partially collapse, which allowed the peptide to escape from the affected pores.

The peptide molecules carry small charges, and once outside the framework these allow the molecules to self-assemble into a structure that repels water.

This reduces the surface tension in the immediate area and pushes the whole structure towards the region of higher tension. ‘Essentially, the peptides form a tail that pushes the particles along,’ Matsui said in a statement.

Matsui thinks that the device’s propulsion effect could be used in reverse, by coating the surface of the MOF with an agent that pulls in desired molecules.

‘If you had a target molecule on the surface [of the water] that could be pulled into the cage of the MOF, this could create the gradient to drive propulsion,’ he said. ‘One could maybe envisage a micro-robot as a method to clean up pollution, for example.’