Synthesis and Self-Assembly of Janus Au-Fe₃O₄ Nanoparticles

We have developed methods to fabricate Janus nanoparticles. In one example, Janus Au-Fe₃O₄ dumbbell nanocrystals (< 20 nm) were synthesized with the hydrophobic ligands coated on the Au lobe and negatively charged hydrophilic ligands coated on the Fe₃O₄ lobe. We can control the self-assembly of nanoparticles in aqueous solutions by systematically balancing the hydrophobic and hydrophilic moieties. The strong interparticle plasmonic coupling displayed a red-shift in surface plasmon resonance, with larger structures formed by Au-Au-Fe₃O₄ assembly extending into the near-infrared region.