Nanovalve Principle (IMAGE) Wiley Caption pH-controllable nanovalves that operate in water have been produced by attaching [2]pseudorotaxanes to the surface of mesoporous silica nanoparticles. The nanovalves are able to contain guest molecules (rhodamine B, red circles) within the nanopores at acidic and neutral pH values but release them on command when the pH value is raised. Credit (C) Wiley-VCH 2008 Usage Restrictions Permission to use with appropriate credit and link to http://dx.doi.org/10.1002/anie.200705211 License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.