Slowing Down Water: Enhanced and Cation-responsive MRI Contrast.

The confinement of paramagnetic centres to the internal channels of mesoporous nanoparticles brings with it a much greater contribution from outer sphere effects by virtue of tuneable side wall association and a resulting much stretched water diffusion coefficient. We specifically utilise the relative ease of side wall modifications to demonstrate that kosmotropic (water-ordering) effects can be leveraged to greatly increase the viscosity of water in the vicinity of internalised paramagnetic complexes. This has the effect of supporting unprecedented levels of image contrast with q = 0 systems and much enhanced T1 contrast for common q = 1 complexes, at clinically relevant field strengths. Physiologically relevant potassium-responsive imaging was subsequently enabled by modulating the water organisation initially imparted by internalised crown ethers on specific cation binding.