Water gated contrast switching with polymer-silica hybrid nanoparticles.

Bioresponsive contrast agents can provide smart signaling in MRI. In wrapping pore functionalised Gd-DOTA mesoporous silica nanoparticles with pH-responsive poly(acrylic acid), exchange between pore and bulk water can be reversibly switched by local pH. The generated high contrast then exhibits a large amplitude switch in a manner relevant to environmentally responsive imaging.