A highly selective magnetic sensor for Cd2+ in living cells with (Zn, Mn)-doped iron oxide nanoparticles

A magnetic sensor for Cd 2+ has been developed based on (Zn, Mn)-doped iron oxide nanoparticles [(Zn, Mn)Fe 3 O 4 NPs], which was modified by ethyl 1-(2-(3′,4′-dihydroxyphenyl)-2-oxoethyl)-1H-1,2,3-triazole-4-carboxylate (ETC). ETC provided the binding sites to Cd 2+ to induce the transformation of (Zn, Mn)Fe 3 O 4 NPs from a dispersed to an aggregated state with a corresponding increase in the transverse relaxation time ( T 2 ) of surrounding water protons. Owing to the special strong interaction between ETC and Cd 2+ , ETC coordinated (Zn, Mn)Fe 3 O 4 [(ETC-(Zn, Mn)Fe 3 O 4 )] NPs exhibited a low limit of detection of Cd 2+ of 3.5   nM and a high selectivity over other metal ions . Furthermore, ETC-(Zn, Mn)Fe 3 O 4 NPs can be used to detect Cd 2+ in living cells by magnetic resonance (MR) imaging.