Ultrahigh magnetic resonance contrast switching with water gated polymer-silica nanoparticles.

Very high T 1 magnetic resonance imaging (MRI) switches can be obtained with pH-responsive polymer-coated paramagnetic mesoporous silica nanoparticles (MSNs), as the local environment traverses the p K a of the polymer coat (Δ r 1 ∼ 50 mM -1 s -1 at 1.5 T and Δ r 1 ∼ 22 mM -1 s -1 at 3 T). We assign these characteristics to a strong peripheral hydration capping at the mesopores, impacting channel-confined water mobility such that outer sphere contributions to contrast are greatly enhanced.