Mn(II) complex impregnated porous silica nanoparticles as Zn(II)-responsive "Smart" MRI contrast agent for pancreas...

Type-1 and type-2 diabetes mellitus are metabolic disorders governed by the functional efficiency of pancreatic β-cells. The activities of the cells toward insulin production, storage, and secretion are accompanied by Zn(II) ions. Thus, for non-invasive pathology of the cell, developing Zn(II) ion-responsive MRI-contrast agents has earned considerable interest. In this report, we have synthesized a seven-coordinate, mono(aquated) Mn(II) complex (1), which is impregnated within a porous silica nanosphere of size 13.2 nm to engender the Mn(II)-based MRI contrast agent, complex 1@SiO₂NP. The surface functionalization of the nanosphere by the Py₂Pic organic moiety for the selective binding of Zn(II)-ions yields complex 1@SiO₂-Py₂PicNP, which exhibits r₁ = 13.19 mM^-1 s^-1. The relaxivity value elevates to 20.38 mM^-1 s^-1 in the presence of 0.6 mM BSA protein at pH 7.4. Gratifyingly, r₁ increases linearly with the increase of Zn(II) ion concentration and reaches 39.01 mM^-1 s^-1 in the presence of a 40 fold excess of the ions. Thus, Zn(II)-responsive contrast enhancement in vivo is envisaged by employing the nanoparticle. Indeed, a contrast enhancement in the pancreas is observed when complex 1@SiO₂-Py₂PicNP and a glucose stimulus are administered in fasted healthy C57BL/6 mice at 7 T.