MOF based motorboat


Researchers from the US and Japan have devised a new type of molecular motor capable of propelling itself across a liquid surface. The move marks another step along the road towards mimicking motile life forms found in nature, such as bacteria, in the quest for autonomous microscopic machines.

The team, led by Hiroshi Matsui of Hunter College, City University of New York, loaded the pores of a metal-organic framework (MOF) with the peptide diphenylalanine and floated the particles on water. When they introduced sodium ethylenediaminetetraacetate (EDTA) to the water this partially degraded the MOF, causing the peptide to leak out. Upon reaching the water, the peptide spontaneously reassembles into a hydrophobic aggregate, reducing the surface tension at that point. The creation of a surface-tension gradient forces the particles to move towards the area with higher surface tension, a phenomenon known as the Marangoni effect.

MOF motor

As the peptide is released it forms a hydrophobic aggregate, propelling the boat using a surface tension gradient

‘Essentially the reassembled peptide forms a tail which pushes the particles along,’ says Matsui. The team fabricated a tiny plastic boat with a slit in one end and loaded it with a MOF-peptide fuel tank. Degradation of the MOF caused the peptide to flow out of the aperture on the boat, propelling the vessel forward.

Matsui says that an intriguing possibility would be to create a surface-tension gradient on a liquid surface not by leaking molecules out of a MOF, but by drawing them in. ‘If you had a target molecule on the surface that could be pulled into the cage of the MOF, this could create the gradient to provide propulsion. One could maybe envisage such a micro-robot as a method to clean up a pollutant, for example.’ The team is now working on such an approach.

Experts on molecular self-propulsion are impressed by the work. Robin Ras, of Aalto University in Finland, earlier this year demonstrated a Marangoni-propelled boat using ethanol vapour to reduce surface tension. ‘Of particular interest is that they use a biological fuel and that they designed a system in which the fuel can be released in a slow and controlled manner, leading to propulsion for an extended time,’ says Ras.

Orlin Velev of North Carolina State University in the US notes that there is growing interest in creating ‘active, responsive and smart structures.’ The new work is ‘important not because it has an immediate application, but in revealing new levels of complexity in the design and synthesis of active materials.’

Ray Kapral at the University of Toronto in Canada, comments, ‘One of the  challenges in this field is to find new fuels for the propulsion of motors and this paper suggests a novel fuel source. Reactions in the environment play an important role for biological motors and that the same is true for this synthetic motor.’


Related Content

Surfactant driven propulsion

14 June 2012 Research

news image

Vapour-driven Marangoni motion offers prolonged propulsion for a small boat

Magic MOFs

28 January 2009 Premium contentFeature

news image

Metal organic frameworks are molecular mops that have the potential to solve some of the world's most pressing environmental ...

Most Read

Isotope effect produces new type of chemical bond

22 October 2014 Research

news image

Evidence emerges for vibrational bond first proposed 30 years ago

DNA 'barcodes' used to track food

30 October 2014 Research

news image

Milk has been successfully tracked as it is turned into cheese and yogurt in an advance that could fight food fraud

Most Commented

Square planar iron complex breaks inorganic dogma

31 October 2014 Research

news image

Unusual spin state could open the door to new and exciting chemistry

Indian U-turn on diabetes drug ban

16 August 2013 News and Analysis

news image

Suspension of cheap and popular medicine reversed but will now come with new safety warnings