Non-specific Zn²⁺ ion sensing using ultrasmall gadolinium oxide nanoparticle as a magnetic resonance imaging contrast agent

The gadolinium oxide (Gd₂O₃) nanoparticles are well-known potential candidates for a positive magnetic resonance imaging (MRI) contrast agent owing to their large longitudinal water proton relaxivity (r₁) value with r₂/r₁ ratio close to one (r₂ = transverse water proton relaxivity). In addition they may be used to sense metal ions because their r₁ and r₂ values can be altered in the presence of metal ions. This may allow us to study metabolic processes involving metal ions and to diagnose disease related to abnormal concentrations of metal ions in the body in a non-invasive way. In this study ultrasmall Gd₂O₃ nanoparticles were for the first time applied to non-specifically sense Zn²⁺ ions in aqueous solution. We explored this by measuring r₁ and r₂ values in the presence of Zn²⁺ ions in solution.