Aug 1, 2005
Nanovalve has light response
Researchers at the Biomade Technology Foundation and the University of Groningen, both in the Netherlands, have made a molecular valve that opens and closes in response to light. The nanovalve could have applications in controllable drug delivery or nanofluidic and microfluidic devices.
"Considering the great current interest in nanodevices and molecular-based machines, it is evident that a controllable nanovalve will be a key component of the nano-toolbox," Ben Feringa of the University of Groningen told nanotechweb.org. "Realizing that the membranes of our cells are full of valves and channels used for transport, it is not too far-fetched to build a hybrid system based on a natural channel protein and introduce a photoswitch to control the valve's opening and closing."
Feringa and colleagues used a channel protein from the Escherichia coli bacterium. Normally, the mechanosensitive channel of large conductance protein opens and closes a 3 nm-diameter pore to relieve the build-up of hydrostatic pressure inside the bacterial cell.
The researchers modified the protein with photosensitive compounds. Illuminating these compounds with light led to a build-up of charge, causing the valve to open. One of the compounds was reversible: illumination with light of a different wavelength caused the removal of the charge and closing of the valve.
To test the valve's response, the team incorporated a non-reversible valve into a liposomal membrane containing a fluorescent dye. Some dye leakage occurred under ambient conditions, but illuminating the valve with light with a wavelength of 366 nm caused the release of 43% of the liposome's content. Under the same test conditions, the reversible valve released a smaller percentage of the liposome's contents, probably because it had a higher hydrophobicity than the one-way switch.
"The construction of capsules that act as a container for a drug, but have valves that can be opened on command to release the drug, is within reach with our present findings," said Feringa. "The details of the mechanism of channel opening/closing under light [irradiation] will be studied, including factors governing the valve function."
The researchers reported their work in Science.
About the author
Liz Kalaugher is editor of nanotechweb.org.