Fig. 11.

Schematic summary of the protein gating of MSNs. Externally biotinylated Gd–DOTA MSNs enjoy good water accessibility and a high relaxivity that can be reversibly capped by the steric bulk of bound streptavidin. In the presence of low μM of biotinylated BSA, the gating protein is competed off the particle surface and relaxivity recovers. Adapted from ref. 111 with permission from The Royal Society of Chemistry.