Nanoparticles have been designed to act as AND logic gates — requiring both light and pH changes before releasing cargo from their nanopores
Molecular systems that release cargo have great potential for targeted drug delivery. Those that respond to a single external stimulus are well known but a system that requires two triggers for release — creating an AND molecular logic gate — would give improved control as it could respond to both external and biological triggers. Now, a collaboration between Fraser Stoddart at Northwestern University and Jeffrey Zink at the University of California, Los Angeles, has led to the development1 of a system that needs both light and a change in pH to release a guest.
The system uses azobenzene-derived molecules — tethered to the inside of pores within mesoporous silica nanoparticles — to act as 'nanoimpellers' that drive any guest cargo out. Azobenzene can change between cis and trans forms on absorption of light, and a 'wagging' motion is induced when a wavelength is used that is absorbed by both.
The pore, however, is also blocked with a pseudorotaxane tethered to the outer surface of the nanoparticle. This creates a nanovalve that opens on changes in pH, releasing the ring from the stalk of the pseudorotaxane by disrupting their mutual bonding. Both triggers are required for release and this was proved using a fluorescent bipyridine-derived guest molecule that was detected using luminescence spectroscopy.
Angelos, S., Yang, Y.-W., Khashab, N. M., Stoddart, J. F. & Zink, J. I. Dual-controlled nanoparticles exhibiting AND logic J. Am. Chem. Soc. 10.1021/ja9042752 (2009)