Gold Nanoparticles Coated with Manganese–Porphyrin That Effectively Shorten the Longitudinal Relaxation Time of Water Molecules Depending on the Particle Size

In order to develop gold nanoparticles that effectively accelerate the longitudinal relaxation of water protons, we have prepared gold nanoparticles coated with a monolayer of manganese(III)–porphyrin that can form four Au–S bonds on the gold surface. The particle size can be easily controlled via the initial S/Au ratio before reduction. The longitudinal relaxivity per Mn clearly increased with the particle size due to the rigid anchoring of manganese(III)–porphyrin via four Au–S bonds.