Development of Iron-Doped Silicon Nanoparticles As Bimodal Imaging Agents

We demonstrate the synthesis of water-soluble allylamine-terminated Fe-doped Si (Si-xFe) nanoparticles as bimodal agents for optical and magnetic imaging. The preparation involves the synthesis of a single-source iron-containing precursor, Na4Si4 with x% Fe (x = 1, 5, 10), and its subsequent reaction with NH4Br to produce hydrogen-terminated Si-xFe nanoparticles. The hydrogen-capped nanoparticles are further terminated with allylamine via thermal hydrosilylation. Transmission electron microscopy indicates that the average particle diameter is similar to 3.0 +/- 1.0 nm. The Si-5Fe nanoparticles show strong photoluminescence quantum yield in water (similar to 10%) with significant T-2 contrast (r(2)/r(1), value of 4.31). Electron paramagnetic resonance and Mossbauer spectroscopies indicate that iron in the nanoparticles is in the +3 oxidation state. Analysis of cytotoxicity using the resazurin assay on HepG2 liver cells indicates that the particles have minimal toxicity.