Manganese doped fluorescent paramagnetic nanocrystals for dual-modal imaging

I n this work, dual-modal (fl uorescence and magnetic resonance) imaging capabilities of water-soluble, low-toxicity, monodisperse Mn-doped ZnSe nanocrystals (NCs) with a size (6.5 nm) below the optimum kidney cutoff limit (10 nm) are reported. Synthesizing Mn-doped ZnSe NCs with varying Mn 2+ concentrations, a systematic investigation of the optical properties of these NCs by using photoluminescence (PL) and time resolved fl uorescence are demonstrated. The elemental properties of these NCs using X-ray photoelectron spectroscopy and inductive coupled plasma-mass spectroscopy confi rming Mn 2+ doping is confi ned to the core of these NCs are also presented. It is observed that with increasing Mn 2+ concentration the PL intensity fi rst increases, reaching a maximum at Mn 2+ concentration of 3.2 at% (achieving a PL quantum yield (QY) of 37%), after which it starts to decrease. Here, this high-effi ciency sample is demonstrated for applications in dual-modal imaging. These NCs are further made water-soluble by ligand exchange using 3-mercaptopropionic acid, preserving their PL QY as high as 18%. At the same time, these NCs exhibit high relaxivity (≈2.95 mM −1 s −1 ) to obtain MR contrast at 25 °C, 3 T. Therefore, the Mn 2+ doping in these water-soluble Cd-free NCs are suffi cient to produce contrast for both fl uorescence and magnetic resonance imaging techniques.