Size-controlled syntheses and hydrophilic surface modification of Fe ₃O₄, Ag, and Fe₃O₄/Ag heterodimer nanocrystals

High-quality, monodisperse, and size-controlled Fe₃O ₄, Ag, and bifunctional Fe₃O₄/Ag heterodimer nanocrystals (NCs) have been synthesized successfully. In the synthesis of Fe₃O₄ NCs, dodecanol was chosen as the substitute of 1,2-hexadecanediol and "size control" was achieved by simply adjusting the proportion among the ligands instead of utilizing seed-mediated growth. In the synthesis of Ag NCs, organometallic silver acetylacetonate (Agacac) was used as precursors and tunable particle size could be easily obtained by adjusting the reaction temperatures. By using different sized Fe₃O₄ NCs as seeds, Fe₃O₄/Ag heterodimer NCs with particle sizes tuned from 5 to 16 nm for Fe₃O₄ and 4 to 8 nm for Ag were successfully synthesized and superparamagnetism were maintained. We found that the size of Ag attached on the Fe₃O₄ NCs relied on the size of Fe₃O₄ seed. UV-vis absorption spectra and TEM investigations revealed that the bigger the Fe₃O₄ NCs seed used, the bigger the Ag NCs that were obtained from the heterodimer NCs. In addition, we demonstrated that all of these NCs were successfully transferred into water by surface modification with biocompatible carboxylic acid groups, which made them meet the basic requirement for biolabeling and biomedical applications.